text: /*
  ** 2001 September 15
  **
  ** The author disclaims copyright to this source code.  In place of
  ** a legal notice, here is a blessing:
  **
  **    May you do good and not evil.
  **    May you find forgiveness for yourself and forgive others.
  **    May you share freely, never taking more than you give.
  **
  *************************************************************************
  ** This file contains C code routines that are called by the parser
  ** to handle SELECT statements in SQLite.
  */
  #include "sqliteInt.h"
  
  /*
  ** An instance of the following object is used to record information about
  ** how to process the DISTINCT keyword, to simplify passing that information
  ** into the selectInnerLoop() routine.
  */
  typedef struct DistinctCtx DistinctCtx;
  struct DistinctCtx {
    u8 isTnct;      /* True if the DISTINCT keyword is present */
    u8 eTnctType;   /* One of the WHERE_DISTINCT_* operators */
    int tabTnct;    /* Ephemeral table used for DISTINCT processing */
    int addrTnct;   /* Address of OP_OpenEphemeral opcode for tabTnct */
  };
  
  /*
  ** An instance of the following object is used to record information about
  ** the ORDER BY (or GROUP BY) clause of query is being coded.
  **
  ** The aDefer[] array is used by the sorter-references optimization. For
  ** example, assuming there is no index that can be used for the ORDER BY,
  ** for the query:
  **
  **     SELECT a, bigblob FROM t1 ORDER BY a LIMIT 10;
  **
  ** it may be more efficient to add just the "a" values to the sorter, and
  ** retrieve the associated "bigblob" values directly from table t1 as the
  ** 10 smallest "a" values are extracted from the sorter.
  **
  ** When the sorter-reference optimization is used, there is one entry in the
  ** aDefer[] array for each database table that may be read as values are
  ** extracted from the sorter.
  */
  typedef struct SortCtx SortCtx;
  struct SortCtx {
    ExprList *pOrderBy;   /* The ORDER BY (or GROUP BY clause) */
    int nOBSat;           /* Number of ORDER BY terms satisfied by indices */
    int iECursor;         /* Cursor number for the sorter */
    int regReturn;        /* Register holding block-output return address */
    int labelBkOut;       /* Start label for the block-output subroutine */
    int addrSortIndex;    /* Address of the OP_SorterOpen or OP_OpenEphemeral */
    int labelDone;        /* Jump here when done, ex: LIMIT reached */
    int labelOBLopt;      /* Jump here when sorter is full */
    u8 sortFlags;         /* Zero or more SORTFLAG_* bits */
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
    u8 nDefer;            /* Number of valid entries in aDefer[] */
    struct DeferredCsr {
      Table *pTab;        /* Table definition */
      int iCsr;           /* Cursor number for table */
      int nKey;           /* Number of PK columns for table pTab (>=1) */
    } aDefer[4];
  #endif
    struct RowLoadInfo *pDeferredRowLoad;  /* Deferred row loading info or NULL */
  };
  #define SORTFLAG_UseSorter  0x01   /* Use SorterOpen instead of OpenEphemeral */
  
  /*
  ** Delete all the content of a Select structure.  Deallocate the structure
  ** itself depending on the value of bFree
  **
  ** If bFree==1, call sqlite3DbFree() on the p object.
  ** If bFree==0, Leave the first Select object unfreed
  */
  static void clearSelect(sqlite3 *db, Select *p, int bFree){
    while( p ){
      Select *pPrior = p->pPrior;
      sqlite3ExprListDelete(db, p->pEList);
      sqlite3SrcListDelete(db, p->pSrc);
      sqlite3ExprDelete(db, p->pWhere);
      sqlite3ExprListDelete(db, p->pGroupBy);
      sqlite3ExprDelete(db, p->pHaving);
      sqlite3ExprListDelete(db, p->pOrderBy);
      sqlite3ExprDelete(db, p->pLimit);
      if( OK_IF_ALWAYS_TRUE(p->pWith) ) sqlite3WithDelete(db, p->pWith);
  #ifndef SQLITE_OMIT_WINDOWFUNC
      if( OK_IF_ALWAYS_TRUE(p->pWinDefn) ){
        sqlite3WindowListDelete(db, p->pWinDefn);
      }
      while( p->pWin ){
        assert( p->pWin->ppThis==&p->pWin );
        sqlite3WindowUnlinkFromSelect(p->pWin);
      }
  #endif
      if( bFree ) sqlite3DbFreeNN(db, p);
      p = pPrior;
      bFree = 1;
    }
  }
  
  /*
  ** Initialize a SelectDest structure.
  */
  void sqlite3SelectDestInit(SelectDest *pDest, int eDest, int iParm){
    pDest->eDest = (u8)eDest;
    pDest->iSDParm = iParm;
    pDest->iSDParm2 = 0;
    pDest->zAffSdst = 0;
    pDest->iSdst = 0;
    pDest->nSdst = 0;
  }
  
  
  /*
  ** Allocate a new Select structure and return a pointer to that
  ** structure.
  */
  Select *sqlite3SelectNew(
    Parse *pParse,        /* Parsing context */
    ExprList *pEList,     /* which columns to include in the result */
    SrcList *pSrc,        /* the FROM clause -- which tables to scan */
    Expr *pWhere,         /* the WHERE clause */
    ExprList *pGroupBy,   /* the GROUP BY clause */
    Expr *pHaving,        /* the HAVING clause */
    ExprList *pOrderBy,   /* the ORDER BY clause */
    u32 selFlags,         /* Flag parameters, such as SF_Distinct */
    Expr *pLimit          /* LIMIT value.  NULL means not used */
  ){
    Select *pNew, *pAllocated;
    Select standin;
    pAllocated = pNew = sqlite3DbMallocRawNN(pParse->db, sizeof(*pNew) );
    if( pNew==0 ){
      assert( pParse->db->mallocFailed );
      pNew = &standin;
    }
    if( pEList==0 ){
      pEList = sqlite3ExprListAppend(pParse, 0,
                                     sqlite3Expr(pParse->db,TK_ASTERISK,0));
    }
    pNew->pEList = pEList;
    pNew->op = TK_SELECT;
    pNew->selFlags = selFlags;
    pNew->iLimit = 0;
    pNew->iOffset = 0;
    pNew->selId = ++pParse->nSelect;
    pNew->addrOpenEphm[0] = -1;
    pNew->addrOpenEphm[1] = -1;
    pNew->nSelectRow = 0;
    if( pSrc==0 ) pSrc = sqlite3DbMallocZero(pParse->db, sizeof(*pSrc));
    pNew->pSrc = pSrc;
    pNew->pWhere = pWhere;
    pNew->pGroupBy = pGroupBy;
    pNew->pHaving = pHaving;
    pNew->pOrderBy = pOrderBy;
    pNew->pPrior = 0;
    pNew->pNext = 0;
    pNew->pLimit = pLimit;
    pNew->pWith = 0;
  #ifndef SQLITE_OMIT_WINDOWFUNC
    pNew->pWin = 0;
    pNew->pWinDefn = 0;
  #endif
    if( pParse->db->mallocFailed ) {
      clearSelect(pParse->db, pNew, pNew!=&standin);
      pAllocated = 0;
    }else{
      assert( pNew->pSrc!=0 || pParse->nErr>0 );
    }
    return pAllocated;
  }
  
  
  /*
  ** Delete the given Select structure and all of its substructures.
  */
  void sqlite3SelectDelete(sqlite3 *db, Select *p){
    if( OK_IF_ALWAYS_TRUE(p) ) clearSelect(db, p, 1);
  }
  
  /*
  ** Return a pointer to the right-most SELECT statement in a compound.
  */
  static Select *findRightmost(Select *p){
    while( p->pNext ) p = p->pNext;
    return p;
  }
  
  /*
  ** Given 1 to 3 identifiers preceding the JOIN keyword, determine the
  ** type of join.  Return an integer constant that expresses that type
  ** in terms of the following bit values:
  **
  **     JT_INNER
  **     JT_CROSS
  **     JT_OUTER
  **     JT_NATURAL
  **     JT_LEFT
  **     JT_RIGHT
  **
  ** A full outer join is the combination of JT_LEFT and JT_RIGHT.
  **
  ** If an illegal or unsupported join type is seen, then still return
  ** a join type, but put an error in the pParse structure.
  */
  int sqlite3JoinType(Parse *pParse, Token *pA, Token *pB, Token *pC){
    int jointype = 0;
    Token *apAll[3];
    Token *p;
                               /*   0123456789 123456789 123456789 123 */
    static const char zKeyText[] = "naturaleftouterightfullinnercross";
    static const struct {
      u8 i;        /* Beginning of keyword text in zKeyText[] */
      u8 nChar;    /* Length of the keyword in characters */
      u8 code;     /* Join type mask */
    } aKeyword[] = {
      /* natural */ { 0,  7, JT_NATURAL                },
      /* left    */ { 6,  4, JT_LEFT|JT_OUTER          },
      /* outer   */ { 10, 5, JT_OUTER                  },
      /* right   */ { 14, 5, JT_RIGHT|JT_OUTER         },
      /* full    */ { 19, 4, JT_LEFT|JT_RIGHT|JT_OUTER },
      /* inner   */ { 23, 5, JT_INNER                  },
      /* cross   */ { 28, 5, JT_INNER|JT_CROSS         },
    };
    int i, j;
    apAll[0] = pA;
    apAll[1] = pB;
    apAll[2] = pC;
    for(i=0; i<3 && apAll[i]; i++){
      p = apAll[i];
      for(j=0; j<ArraySize(aKeyword); j++){
        if( p->n==aKeyword[j].nChar 
            && sqlite3StrNICmp((char*)p->z, &zKeyText[aKeyword[j].i], p->n)==0 ){
          jointype |= aKeyword[j].code;
          break;
        }
      }
      testcase( j==0 || j==1 || j==2 || j==3 || j==4 || j==5 || j==6 );
      if( j>=ArraySize(aKeyword) ){
        jointype |= JT_ERROR;
        break;
      }
    }
    if(
       (jointype & (JT_INNER|JT_OUTER))==(JT_INNER|JT_OUTER) ||
       (jointype & JT_ERROR)!=0
    ){
      const char *zSp = " ";
      assert( pB!=0 );
      if( pC==0 ){ zSp++; }
      sqlite3ErrorMsg(pParse, "unknown or unsupported join type: "
         "%T %T%s%T", pA, pB, zSp, pC);
      jointype = JT_INNER;
    }else if( (jointype & JT_OUTER)!=0 
           && (jointype & (JT_LEFT|JT_RIGHT))!=JT_LEFT ){
      sqlite3ErrorMsg(pParse, 
        "RIGHT and FULL OUTER JOINs are not currently supported");
      jointype = JT_INNER;
    }
    return jointype;
  }
  
  /*
  ** Return the index of a column in a table.  Return -1 if the column
  ** is not contained in the table.
  */
  int sqlite3ColumnIndex(Table *pTab, const char *zCol){
    int i;
    u8 h = sqlite3StrIHash(zCol);
    Column *pCol;
    for(pCol=pTab->aCol, i=0; i<pTab->nCol; pCol++, i++){
      if( pCol->hName==h && sqlite3StrICmp(pCol->zName, zCol)==0 ) return i;
    }
    return -1;
  }
  
  /*
  ** Search the first N tables in pSrc, from left to right, looking for a
  ** table that has a column named zCol.  
  **
  ** When found, set *piTab and *piCol to the table index and column index
  ** of the matching column and return TRUE.
  **
  ** If not found, return FALSE.
  */
  static int tableAndColumnIndex(
    SrcList *pSrc,       /* Array of tables to search */
    int N,               /* Number of tables in pSrc->a[] to search */
    const char *zCol,    /* Name of the column we are looking for */
    int *piTab,          /* Write index of pSrc->a[] here */
    int *piCol,          /* Write index of pSrc->a[*piTab].pTab->aCol[] here */
    int bIgnoreHidden    /* True to ignore hidden columns */
  ){
    int i;               /* For looping over tables in pSrc */
    int iCol;            /* Index of column matching zCol */
  
    assert( (piTab==0)==(piCol==0) );  /* Both or neither are NULL */
    for(i=0; i<N; i++){
      iCol = sqlite3ColumnIndex(pSrc->a[i].pTab, zCol);
      if( iCol>=0 
       && (bIgnoreHidden==0 || IsHiddenColumn(&pSrc->a[i].pTab->aCol[iCol])==0)
      ){
        if( piTab ){
          *piTab = i;
          *piCol = iCol;
        }
        return 1;
      }
    }
    return 0;
  }
  
  /*
  ** This function is used to add terms implied by JOIN syntax to the
  ** WHERE clause expression of a SELECT statement. The new term, which
  ** is ANDed with the existing WHERE clause, is of the form:
  **
  **    (tab1.col1 = tab2.col2)
  **
  ** where tab1 is the iSrc'th table in SrcList pSrc and tab2 is the 
  ** (iSrc+1)'th. Column col1 is column iColLeft of tab1, and col2 is
  ** column iColRight of tab2.
  */
  static void addWhereTerm(
    Parse *pParse,                  /* Parsing context */
    SrcList *pSrc,                  /* List of tables in FROM clause */
    int iLeft,                      /* Index of first table to join in pSrc */
    int iColLeft,                   /* Index of column in first table */
    int iRight,                     /* Index of second table in pSrc */
    int iColRight,                  /* Index of column in second table */
    int isOuterJoin,                /* True if this is an OUTER join */
    Expr **ppWhere                  /* IN/OUT: The WHERE clause to add to */
  ){
    sqlite3 *db = pParse->db;
    Expr *pE1;
    Expr *pE2;
    Expr *pEq;
  
    assert( iLeft<iRight );
    assert( pSrc->nSrc>iRight );
    assert( pSrc->a[iLeft].pTab );
    assert( pSrc->a[iRight].pTab );
  
    pE1 = sqlite3CreateColumnExpr(db, pSrc, iLeft, iColLeft);
    pE2 = sqlite3CreateColumnExpr(db, pSrc, iRight, iColRight);
  
    pEq = sqlite3PExpr(pParse, TK_EQ, pE1, pE2);
    if( pEq && isOuterJoin ){
      ExprSetProperty(pEq, EP_FromJoin);
      assert( !ExprHasProperty(pEq, EP_TokenOnly|EP_Reduced) );
      ExprSetVVAProperty(pEq, EP_NoReduce);
      pEq->iRightJoinTable = pE2->iTable;
    }
    *ppWhere = sqlite3ExprAnd(pParse, *ppWhere, pEq);
  }
  
  /*
  ** Set the EP_FromJoin property on all terms of the given expression.
  ** And set the Expr.iRightJoinTable to iTable for every term in the
  ** expression.
  **
  ** The EP_FromJoin property is used on terms of an expression to tell
  ** the LEFT OUTER JOIN processing logic that this term is part of the
  ** join restriction specified in the ON or USING clause and not a part
  ** of the more general WHERE clause.  These terms are moved over to the
  ** WHERE clause during join processing but we need to remember that they
  ** originated in the ON or USING clause.
  **
  ** The Expr.iRightJoinTable tells the WHERE clause processing that the
  ** expression depends on table iRightJoinTable even if that table is not
  ** explicitly mentioned in the expression.  That information is needed
  ** for cases like this:
  **
  **    SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.b AND t1.x=5
  **
  ** The where clause needs to defer the handling of the t1.x=5
  ** term until after the t2 loop of the join.  In that way, a
  ** NULL t2 row will be inserted whenever t1.x!=5.  If we do not
  ** defer the handling of t1.x=5, it will be processed immediately
  ** after the t1 loop and rows with t1.x!=5 will never appear in
  ** the output, which is incorrect.
  */
  void sqlite3SetJoinExpr(Expr *p, int iTable){
    while( p ){
      ExprSetProperty(p, EP_FromJoin);
      assert( !ExprHasProperty(p, EP_TokenOnly|EP_Reduced) );
      ExprSetVVAProperty(p, EP_NoReduce);
      p->iRightJoinTable = iTable;
      if( p->op==TK_FUNCTION && p->x.pList ){
        int i;
        for(i=0; i<p->x.pList->nExpr; i++){
          sqlite3SetJoinExpr(p->x.pList->a[i].pExpr, iTable);
        }
      }
      sqlite3SetJoinExpr(p->pLeft, iTable);
      p = p->pRight;
    } 
  }
  
  /* Undo the work of sqlite3SetJoinExpr(). In the expression p, convert every
  ** term that is marked with EP_FromJoin and iRightJoinTable==iTable into
  ** an ordinary term that omits the EP_FromJoin mark.
  **
  ** This happens when a LEFT JOIN is simplified into an ordinary JOIN.
  */
  static void unsetJoinExpr(Expr *p, int iTable){
    while( p ){
      if( ExprHasProperty(p, EP_FromJoin)
       && (iTable<0 || p->iRightJoinTable==iTable) ){
        ExprClearProperty(p, EP_FromJoin);
      }
      if( p->op==TK_COLUMN && p->iTable==iTable ){
        ExprClearProperty(p, EP_CanBeNull);
      }
      if( p->op==TK_FUNCTION && p->x.pList ){
        int i;
        for(i=0; i<p->x.pList->nExpr; i++){
          unsetJoinExpr(p->x.pList->a[i].pExpr, iTable);
        }
      }
      unsetJoinExpr(p->pLeft, iTable);
      p = p->pRight;
    } 
  }
  
  /*
  ** This routine processes the join information for a SELECT statement.
  ** ON and USING clauses are converted into extra terms of the WHERE clause.
  ** NATURAL joins also create extra WHERE clause terms.
  **
  ** The terms of a FROM clause are contained in the Select.pSrc structure.
  ** The left most table is the first entry in Select.pSrc.  The right-most
  ** table is the last entry.  The join operator is held in the entry to
  ** the left.  Thus entry 0 contains the join operator for the join between
  ** entries 0 and 1.  Any ON or USING clauses associated with the join are
  ** also attached to the left entry.
  **
  ** This routine returns the number of errors encountered.
  */
  static int sqliteProcessJoin(Parse *pParse, Select *p){
    SrcList *pSrc;                  /* All tables in the FROM clause */
    int i, j;                       /* Loop counters */
    SrcItem *pLeft;                 /* Left table being joined */
    SrcItem *pRight;                /* Right table being joined */
  
    pSrc = p->pSrc;
    pLeft = &pSrc->a[0];
    pRight = &pLeft[1];
    for(i=0; i<pSrc->nSrc-1; i++, pRight++, pLeft++){
      Table *pRightTab = pRight->pTab;
      int isOuter;
  
      if( NEVER(pLeft->pTab==0 || pRightTab==0) ) continue;
      isOuter = (pRight->fg.jointype & JT_OUTER)!=0;
  
      /* When the NATURAL keyword is present, add WHERE clause terms for
      ** every column that the two tables have in common.
      */
      if( pRight->fg.jointype & JT_NATURAL ){
        if( pRight->pOn || pRight->pUsing ){
          sqlite3ErrorMsg(pParse, "a NATURAL join may not have "
             "an ON or USING clause", 0);
          return 1;
        }
        for(j=0; j<pRightTab->nCol; j++){
          char *zName;   /* Name of column in the right table */
          int iLeft;     /* Matching left table */
          int iLeftCol;  /* Matching column in the left table */
  
          if( IsHiddenColumn(&pRightTab->aCol[j]) ) continue;
          zName = pRightTab->aCol[j].zName;
          if( tableAndColumnIndex(pSrc, i+1, zName, &iLeft, &iLeftCol, 1) ){
            addWhereTerm(pParse, pSrc, iLeft, iLeftCol, i+1, j,
                  isOuter, &p->pWhere);
          }
        }
      }
  
      /* Disallow both ON and USING clauses in the same join
      */
      if( pRight->pOn && pRight->pUsing ){
        sqlite3ErrorMsg(pParse, "cannot have both ON and USING "
          "clauses in the same join");
        return 1;
      }
  
      /* Add the ON clause to the end of the WHERE clause, connected by
      ** an AND operator.
      */
      if( pRight->pOn ){
        if( isOuter ) sqlite3SetJoinExpr(pRight->pOn, pRight->iCursor);
        p->pWhere = sqlite3ExprAnd(pParse, p->pWhere, pRight->pOn);
        pRight->pOn = 0;
      }
  
      /* Create extra terms on the WHERE clause for each column named
      ** in the USING clause.  Example: If the two tables to be joined are 
      ** A and B and the USING clause names X, Y, and Z, then add this
      ** to the WHERE clause:    A.X=B.X AND A.Y=B.Y AND A.Z=B.Z
      ** Report an error if any column mentioned in the USING clause is
      ** not contained in both tables to be joined.
      */
      if( pRight->pUsing ){
        IdList *pList = pRight->pUsing;
        for(j=0; j<pList->nId; j++){
          char *zName;     /* Name of the term in the USING clause */
          int iLeft;       /* Table on the left with matching column name */
          int iLeftCol;    /* Column number of matching column on the left */
          int iRightCol;   /* Column number of matching column on the right */
  
          zName = pList->a[j].zName;
          iRightCol = sqlite3ColumnIndex(pRightTab, zName);
          if( iRightCol<0
           || !tableAndColumnIndex(pSrc, i+1, zName, &iLeft, &iLeftCol, 0)
          ){
            sqlite3ErrorMsg(pParse, "cannot join using column %s - column "
              "not present in both tables", zName);
            return 1;
          }
          addWhereTerm(pParse, pSrc, iLeft, iLeftCol, i+1, iRightCol,
                       isOuter, &p->pWhere);
        }
      }
    }
    return 0;
  }
  
  /*
  ** An instance of this object holds information (beyond pParse and pSelect)
  ** needed to load the next result row that is to be added to the sorter.
  */
  typedef struct RowLoadInfo RowLoadInfo;
  struct RowLoadInfo {
    int regResult;               /* Store results in array of registers here */
    u8 ecelFlags;                /* Flag argument to ExprCodeExprList() */
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
    ExprList *pExtra;            /* Extra columns needed by sorter refs */
    int regExtraResult;          /* Where to load the extra columns */
  #endif
  };
  
  /*
  ** This routine does the work of loading query data into an array of
  ** registers so that it can be added to the sorter.
  */
  static void innerLoopLoadRow(
    Parse *pParse,             /* Statement under construction */
    Select *pSelect,           /* The query being coded */
    RowLoadInfo *pInfo         /* Info needed to complete the row load */
  ){
    sqlite3ExprCodeExprList(pParse, pSelect->pEList, pInfo->regResult,
                            0, pInfo->ecelFlags);
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
    if( pInfo->pExtra ){
      sqlite3ExprCodeExprList(pParse, pInfo->pExtra, pInfo->regExtraResult, 0, 0);
      sqlite3ExprListDelete(pParse->db, pInfo->pExtra);
    }
  #endif
  }
  
  /*
  ** Code the OP_MakeRecord instruction that generates the entry to be
  ** added into the sorter.
  **
  ** Return the register in which the result is stored.
  */
  static int makeSorterRecord(
    Parse *pParse,
    SortCtx *pSort,
    Select *pSelect,
    int regBase,
    int nBase
  ){
    int nOBSat = pSort->nOBSat;
    Vdbe *v = pParse->pVdbe;
    int regOut = ++pParse->nMem;
    if( pSort->pDeferredRowLoad ){
      innerLoopLoadRow(pParse, pSelect, pSort->pDeferredRowLoad);
    }
    sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase+nOBSat, nBase-nOBSat, regOut);
    return regOut;
  }
  
  /*
  ** Generate code that will push the record in registers regData
  ** through regData+nData-1 onto the sorter.
  */
  static void pushOntoSorter(
    Parse *pParse,         /* Parser context */
    SortCtx *pSort,        /* Information about the ORDER BY clause */
    Select *pSelect,       /* The whole SELECT statement */
    int regData,           /* First register holding data to be sorted */
    int regOrigData,       /* First register holding data before packing */
    int nData,             /* Number of elements in the regData data array */
    int nPrefixReg         /* No. of reg prior to regData available for use */
  ){
    Vdbe *v = pParse->pVdbe;                         /* Stmt under construction */
    int bSeq = ((pSort->sortFlags & SORTFLAG_UseSorter)==0);
    int nExpr = pSort->pOrderBy->nExpr;              /* No. of ORDER BY terms */
    int nBase = nExpr + bSeq + nData;                /* Fields in sorter record */
    int regBase;                                     /* Regs for sorter record */
    int regRecord = 0;                               /* Assembled sorter record */
    int nOBSat = pSort->nOBSat;                      /* ORDER BY terms to skip */
    int op;                            /* Opcode to add sorter record to sorter */
    int iLimit;                        /* LIMIT counter */
    int iSkip = 0;                     /* End of the sorter insert loop */
  
    assert( bSeq==0 || bSeq==1 );
  
    /* Three cases:
    **   (1) The data to be sorted has already been packed into a Record
    **       by a prior OP_MakeRecord.  In this case nData==1 and regData
    **       will be completely unrelated to regOrigData.
    **   (2) All output columns are included in the sort record.  In that
    **       case regData==regOrigData.
    **   (3) Some output columns are omitted from the sort record due to
    **       the SQLITE_ENABLE_SORTER_REFERENCE optimization, or due to the
    **       SQLITE_ECEL_OMITREF optimization, or due to the 
    **       SortCtx.pDeferredRowLoad optimiation.  In any of these cases
    **       regOrigData is 0 to prevent this routine from trying to copy
    **       values that might not yet exist.
    */
    assert( nData==1 || regData==regOrigData || regOrigData==0 );
  
    if( nPrefixReg ){
      assert( nPrefixReg==nExpr+bSeq );
      regBase = regData - nPrefixReg;
    }else{
      regBase = pParse->nMem + 1;
      pParse->nMem += nBase;
    }
    assert( pSelect->iOffset==0 || pSelect->iLimit!=0 );
    iLimit = pSelect->iOffset ? pSelect->iOffset+1 : pSelect->iLimit;
    pSort->labelDone = sqlite3VdbeMakeLabel(pParse);
    sqlite3ExprCodeExprList(pParse, pSort->pOrderBy, regBase, regOrigData,
                            SQLITE_ECEL_DUP | (regOrigData? SQLITE_ECEL_REF : 0));
    if( bSeq ){
      sqlite3VdbeAddOp2(v, OP_Sequence, pSort->iECursor, regBase+nExpr);
    }
    if( nPrefixReg==0 && nData>0 ){
      sqlite3ExprCodeMove(pParse, regData, regBase+nExpr+bSeq, nData);
    }
    if( nOBSat>0 ){
      int regPrevKey;   /* The first nOBSat columns of the previous row */
      int addrFirst;    /* Address of the OP_IfNot opcode */
      int addrJmp;      /* Address of the OP_Jump opcode */
      VdbeOp *pOp;      /* Opcode that opens the sorter */
      int nKey;         /* Number of sorting key columns, including OP_Sequence */
      KeyInfo *pKI;     /* Original KeyInfo on the sorter table */
  
      regRecord = makeSorterRecord(pParse, pSort, pSelect, regBase, nBase);
      regPrevKey = pParse->nMem+1;
      pParse->nMem += pSort->nOBSat;
      nKey = nExpr - pSort->nOBSat + bSeq;
      if( bSeq ){
        addrFirst = sqlite3VdbeAddOp1(v, OP_IfNot, regBase+nExpr); 
      }else{
        addrFirst = sqlite3VdbeAddOp1(v, OP_SequenceTest, pSort->iECursor);
      }
      VdbeCoverage(v);
      sqlite3VdbeAddOp3(v, OP_Compare, regPrevKey, regBase, pSort->nOBSat);
      pOp = sqlite3VdbeGetOp(v, pSort->addrSortIndex);
      if( pParse->db->mallocFailed ) return;
      pOp->p2 = nKey + nData;
      pKI = pOp->p4.pKeyInfo;
      memset(pKI->aSortFlags, 0, pKI->nKeyField); /* Makes OP_Jump testable */
      sqlite3VdbeChangeP4(v, -1, (char*)pKI, P4_KEYINFO);
      testcase( pKI->nAllField > pKI->nKeyField+2 );
      pOp->p4.pKeyInfo = sqlite3KeyInfoFromExprList(pParse,pSort->pOrderBy,nOBSat,
                                             pKI->nAllField-pKI->nKeyField-1);
      pOp = 0; /* Ensure pOp not used after sqltie3VdbeAddOp3() */
      addrJmp = sqlite3VdbeCurrentAddr(v);
      sqlite3VdbeAddOp3(v, OP_Jump, addrJmp+1, 0, addrJmp+1); VdbeCoverage(v);
      pSort->labelBkOut = sqlite3VdbeMakeLabel(pParse);
      pSort->regReturn = ++pParse->nMem;
      sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
      sqlite3VdbeAddOp1(v, OP_ResetSorter, pSort->iECursor);
      if( iLimit ){
        sqlite3VdbeAddOp2(v, OP_IfNot, iLimit, pSort->labelDone);
        VdbeCoverage(v);
      }
      sqlite3VdbeJumpHere(v, addrFirst);
      sqlite3ExprCodeMove(pParse, regBase, regPrevKey, pSort->nOBSat);
      sqlite3VdbeJumpHere(v, addrJmp);
    }
    if( iLimit ){
      /* At this point the values for the new sorter entry are stored
      ** in an array of registers. They need to be composed into a record
      ** and inserted into the sorter if either (a) there are currently
      ** less than LIMIT+OFFSET items or (b) the new record is smaller than 
      ** the largest record currently in the sorter. If (b) is true and there
      ** are already LIMIT+OFFSET items in the sorter, delete the largest
      ** entry before inserting the new one. This way there are never more 
      ** than LIMIT+OFFSET items in the sorter.
      **
      ** If the new record does not need to be inserted into the sorter,
      ** jump to the next iteration of the loop. If the pSort->labelOBLopt
      ** value is not zero, then it is a label of where to jump.  Otherwise,
      ** just bypass the row insert logic.  See the header comment on the
      ** sqlite3WhereOrderByLimitOptLabel() function for additional info.
      */
      int iCsr = pSort->iECursor;
      sqlite3VdbeAddOp2(v, OP_IfNotZero, iLimit, sqlite3VdbeCurrentAddr(v)+4);
      VdbeCoverage(v);
      sqlite3VdbeAddOp2(v, OP_Last, iCsr, 0);
      iSkip = sqlite3VdbeAddOp4Int(v, OP_IdxLE,
                                   iCsr, 0, regBase+nOBSat, nExpr-nOBSat);
      VdbeCoverage(v);
      sqlite3VdbeAddOp1(v, OP_Delete, iCsr);
    }
    if( regRecord==0 ){
      regRecord = makeSorterRecord(pParse, pSort, pSelect, regBase, nBase);
    }
    if( pSort->sortFlags & SORTFLAG_UseSorter ){
      op = OP_SorterInsert;
    }else{
      op = OP_IdxInsert;
    }
    sqlite3VdbeAddOp4Int(v, op, pSort->iECursor, regRecord,
                         regBase+nOBSat, nBase-nOBSat);
    if( iSkip ){
      sqlite3VdbeChangeP2(v, iSkip,
           pSort->labelOBLopt ? pSort->labelOBLopt : sqlite3VdbeCurrentAddr(v));
    }
  }
  
  /*
  ** Add code to implement the OFFSET
  */
  static void codeOffset(
    Vdbe *v,          /* Generate code into this VM */
    int iOffset,      /* Register holding the offset counter */
    int iContinue     /* Jump here to skip the current record */
  ){
    if( iOffset>0 ){
      sqlite3VdbeAddOp3(v, OP_IfPos, iOffset, iContinue, 1); VdbeCoverage(v);
      VdbeComment((v, "OFFSET"));
    }
  }
  
  /*
  ** Add code that will check to make sure the array of registers starting at
  ** iMem form a distinct entry. This is used by both "SELECT DISTINCT ..." and
  ** distinct aggregates ("SELECT count(DISTINCT <expr>) ..."). Three strategies
  ** are available. Which is used depends on the value of parameter eTnctType,
  ** as follows:
  **
  **   WHERE_DISTINCT_UNORDERED/WHERE_DISTINCT_NOOP:
  **     Build an ephemeral table that contains all entries seen before and
  **     skip entries which have been seen before.
  **
  **     Parameter iTab is the cursor number of an ephemeral table that must
  **     be opened before the VM code generated by this routine is executed.
  **     The ephemeral cursor table is queried for a record identical to the
  **     record formed by the current array of registers. If one is found,
  **     jump to VM address addrRepeat. Otherwise, insert a new record into
  **     the ephemeral cursor and proceed.
  **
  **     The returned value in this case is a copy of parameter iTab.
  **
  **   WHERE_DISTINCT_ORDERED:
  **     In this case rows are being delivered sorted order. The ephermal
  **     table is not required. Instead, the current set of values
  **     is compared against previous row. If they match, the new row
  **     is not distinct and control jumps to VM address addrRepeat. Otherwise,
  **     the VM program proceeds with processing the new row.
  **
  **     The returned value in this case is the register number of the first
  **     in an array of registers used to store the previous result row so that
  **     it can be compared to the next. The caller must ensure that this
  **     register is initialized to NULL.  (The fixDistinctOpenEph() routine
  **     will take care of this initialization.)
  **
  **   WHERE_DISTINCT_UNIQUE:
  **     In this case it has already been determined that the rows are distinct.
  **     No special action is required. The return value is zero.
  **
  ** Parameter pEList is the list of expressions used to generated the 
  ** contents of each row. It is used by this routine to determine (a) 
  ** how many elements there are in the array of registers and (b) the 
  ** collation sequences that should be used for the comparisons if 
  ** eTnctType is WHERE_DISTINCT_ORDERED.
  */
  static int codeDistinct(
    Parse *pParse,     /* Parsing and code generating context */
    int eTnctType,     /* WHERE_DISTINCT_* value */
    int iTab,          /* A sorting index used to test for distinctness */
    int addrRepeat,    /* Jump to here if not distinct */
    ExprList *pEList,  /* Expression for each element */
    int regElem        /* First element */
  ){
    int iRet = 0;
    int nResultCol = pEList->nExpr;
    Vdbe *v = pParse->pVdbe;
  
    switch( eTnctType ){
      case WHERE_DISTINCT_ORDERED: {
        int i;
        int iJump;              /* Jump destination */
        int regPrev;            /* Previous row content */
  
        /* Allocate space for the previous row */
        iRet = regPrev = pParse->nMem+1;
        pParse->nMem += nResultCol;
  
        iJump = sqlite3VdbeCurrentAddr(v) + nResultCol;
        for(i=0; i<nResultCol; i++){
          CollSeq *pColl = sqlite3ExprCollSeq(pParse, pEList->a[i].pExpr);
          if( i<nResultCol-1 ){
            sqlite3VdbeAddOp3(v, OP_Ne, regElem+i, iJump, regPrev+i);
            VdbeCoverage(v);
          }else{
            sqlite3VdbeAddOp3(v, OP_Eq, regElem+i, addrRepeat, regPrev+i);
            VdbeCoverage(v);
           }
          sqlite3VdbeChangeP4(v, -1, (const char *)pColl, P4_COLLSEQ);
          sqlite3VdbeChangeP5(v, SQLITE_NULLEQ);
        }
        assert( sqlite3VdbeCurrentAddr(v)==iJump || pParse->db->mallocFailed );
        sqlite3VdbeAddOp3(v, OP_Copy, regElem, regPrev, nResultCol-1);
        break;
      }
  
      case WHERE_DISTINCT_UNIQUE: {
        /* nothing to do */
        break;
      }
  
      default: {
        int r1 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp4Int(v, OP_Found, iTab, addrRepeat, regElem, nResultCol);
        VdbeCoverage(v);
        sqlite3VdbeAddOp3(v, OP_MakeRecord, regElem, nResultCol, r1);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iTab, r1, regElem, nResultCol);
        sqlite3VdbeChangeP5(v, OPFLAG_USESEEKRESULT);
        sqlite3ReleaseTempReg(pParse, r1);
        iRet = iTab;
        break;
      }
    }
  
    return iRet;
  }
  
  /*
  ** This routine runs after codeDistinct().  It makes necessary
  ** adjustments to the OP_OpenEphemeral opcode that the codeDistinct()
  ** routine made use of.  This processing must be done separately since
  ** sometimes codeDistinct is called before the OP_OpenEphemeral is actually
  ** laid down.
  **
  ** WHERE_DISTINCT_NOOP:
  ** WHERE_DISTINCT_UNORDERED:
  **
  **     No adjustments necessary.  This function is a no-op.
  **
  ** WHERE_DISTINCT_UNIQUE:
  **
  **     The ephemeral table is not needed.  So change the
  **     OP_OpenEphemeral opcode into an OP_Noop.
  **
  ** WHERE_DISTINCT_ORDERED:
  **
  **     The ephemeral table is not needed.  But we do need register
  **     iVal to be initialized to NULL.  So change the OP_OpenEphemeral
  **     into an OP_Null on the iVal register.
  */
  static void fixDistinctOpenEph(
    Parse *pParse,     /* Parsing and code generating context */
    int eTnctType,     /* WHERE_DISTINCT_* value */
    int iVal,          /* Value returned by codeDistinct() */
    int iOpenEphAddr   /* Address of OP_OpenEphemeral instruction for iTab */
  ){
    if( eTnctType==WHERE_DISTINCT_UNIQUE || eTnctType==WHERE_DISTINCT_ORDERED ){
      Vdbe *v = pParse->pVdbe;
      sqlite3VdbeChangeToNoop(v, iOpenEphAddr);
      if( sqlite3VdbeGetOp(v, iOpenEphAddr+1)->opcode==OP_Explain ){
        sqlite3VdbeChangeToNoop(v, iOpenEphAddr+1);
      }
      if( eTnctType==WHERE_DISTINCT_ORDERED ){
        /* Change the OP_OpenEphemeral to an OP_Null that sets the MEM_Cleared 
        ** bit on the first register of the previous value.  This will cause the
        ** OP_Ne added in codeDistinct() to always fail on the first iteration of
        ** the loop even if the first row is all NULLs.  */
        VdbeOp *pOp = sqlite3VdbeGetOp(v, iOpenEphAddr);
        pOp->opcode = OP_Null;
        pOp->p1 = 1;
        pOp->p2 = iVal;
      }
    }
  }
  
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
  /*
  ** This function is called as part of inner-loop generation for a SELECT
  ** statement with an ORDER BY that is not optimized by an index. It 
  ** determines the expressions, if any, that the sorter-reference 
  ** optimization should be used for. The sorter-reference optimization
  ** is used for SELECT queries like:
  **
  **   SELECT a, bigblob FROM t1 ORDER BY a LIMIT 10
  **
  ** If the optimization is used for expression "bigblob", then instead of
  ** storing values read from that column in the sorter records, the PK of
  ** the row from table t1 is stored instead. Then, as records are extracted from
  ** the sorter to return to the user, the required value of bigblob is
  ** retrieved directly from table t1. If the values are very large, this 
  ** can be more efficient than storing them directly in the sorter records.
  **
  ** The ExprList_item.bSorterRef flag is set for each expression in pEList 
  ** for which the sorter-reference optimization should be enabled. 
  ** Additionally, the pSort->aDefer[] array is populated with entries
  ** for all cursors required to evaluate all selected expressions. Finally.
  ** output variable (*ppExtra) is set to an expression list containing
  ** expressions for all extra PK values that should be stored in the
  ** sorter records.
  */
  static void selectExprDefer(
    Parse *pParse,                  /* Leave any error here */
    SortCtx *pSort,                 /* Sorter context */
    ExprList *pEList,               /* Expressions destined for sorter */
    ExprList **ppExtra              /* Expressions to append to sorter record */
  ){
    int i;
    int nDefer = 0;
    ExprList *pExtra = 0;
    for(i=0; i<pEList->nExpr; i++){
      struct ExprList_item *pItem = &pEList->a[i];
      if( pItem->u.x.iOrderByCol==0 ){
        Expr *pExpr = pItem->pExpr;
        Table *pTab = pExpr->y.pTab;
        if( pExpr->op==TK_COLUMN && pExpr->iColumn>=0 && pTab && !IsVirtual(pTab)
         && (pTab->aCol[pExpr->iColumn].colFlags & COLFLAG_SORTERREF)
        ){
          int j;
          for(j=0; j<nDefer; j++){
            if( pSort->aDefer[j].iCsr==pExpr->iTable ) break;
          }
          if( j==nDefer ){
            if( nDefer==ArraySize(pSort->aDefer) ){
              continue;
            }else{
              int nKey = 1;
              int k;
              Index *pPk = 0;
              if( !HasRowid(pTab) ){
                pPk = sqlite3PrimaryKeyIndex(pTab);
                nKey = pPk->nKeyCol;
              }
              for(k=0; k<nKey; k++){
                Expr *pNew = sqlite3PExpr(pParse, TK_COLUMN, 0, 0);
                if( pNew ){
                  pNew->iTable = pExpr->iTable;
                  pNew->y.pTab = pExpr->y.pTab;
                  pNew->iColumn = pPk ? pPk->aiColumn[k] : -1;
                  pExtra = sqlite3ExprListAppend(pParse, pExtra, pNew);
                }
              }
              pSort->aDefer[nDefer].pTab = pExpr->y.pTab;
              pSort->aDefer[nDefer].iCsr = pExpr->iTable;
              pSort->aDefer[nDefer].nKey = nKey;
              nDefer++;
            }
          }
          pItem->bSorterRef = 1;
        }
      }
    }
    pSort->nDefer = (u8)nDefer;
    *ppExtra = pExtra;
  }
  #endif
  
  /*
  ** This routine generates the code for the inside of the inner loop
  ** of a SELECT.
  **
  ** If srcTab is negative, then the p->pEList expressions
  ** are evaluated in order to get the data for this row.  If srcTab is
  ** zero or more, then data is pulled from srcTab and p->pEList is used only 
  ** to get the number of columns and the collation sequence for each column.
  */
  static void selectInnerLoop(
    Parse *pParse,          /* The parser context */
    Select *p,              /* The complete select statement being coded */
    int srcTab,             /* Pull data from this table if non-negative */
    SortCtx *pSort,         /* If not NULL, info on how to process ORDER BY */
    DistinctCtx *pDistinct, /* If not NULL, info on how to process DISTINCT */
    SelectDest *pDest,      /* How to dispose of the results */
    int iContinue,          /* Jump here to continue with next row */
    int iBreak              /* Jump here to break out of the inner loop */
  ){
    Vdbe *v = pParse->pVdbe;
    int i;
    int hasDistinct;            /* True if the DISTINCT keyword is present */
    int eDest = pDest->eDest;   /* How to dispose of results */
    int iParm = pDest->iSDParm; /* First argument to disposal method */
    int nResultCol;             /* Number of result columns */
    int nPrefixReg = 0;         /* Number of extra registers before regResult */
    RowLoadInfo sRowLoadInfo;   /* Info for deferred row loading */
  
    /* Usually, regResult is the first cell in an array of memory cells
    ** containing the current result row. In this case regOrig is set to the
    ** same value. However, if the results are being sent to the sorter, the
    ** values for any expressions that are also part of the sort-key are omitted
    ** from this array. In this case regOrig is set to zero.  */
    int regResult;              /* Start of memory holding current results */
    int regOrig;                /* Start of memory holding full result (or 0) */
  
    assert( v );
    assert( p->pEList!=0 );
    hasDistinct = pDistinct ? pDistinct->eTnctType : WHERE_DISTINCT_NOOP;
    if( pSort && pSort->pOrderBy==0 ) pSort = 0;
    if( pSort==0 && !hasDistinct ){
      assert( iContinue!=0 );
      codeOffset(v, p->iOffset, iContinue);
    }
  
    /* Pull the requested columns.
    */
    nResultCol = p->pEList->nExpr;
  
    if( pDest->iSdst==0 ){
      if( pSort ){
        nPrefixReg = pSort->pOrderBy->nExpr;
        if( !(pSort->sortFlags & SORTFLAG_UseSorter) ) nPrefixReg++;
        pParse->nMem += nPrefixReg;
      }
      pDest->iSdst = pParse->nMem+1;
      pParse->nMem += nResultCol;
    }else if( pDest->iSdst+nResultCol > pParse->nMem ){
      /* This is an error condition that can result, for example, when a SELECT
      ** on the right-hand side of an INSERT contains more result columns than
      ** there are columns in the table on the left.  The error will be caught
      ** and reported later.  But we need to make sure enough memory is allocated
      ** to avoid other spurious errors in the meantime. */
      pParse->nMem += nResultCol;
    }
    pDest->nSdst = nResultCol;
    regOrig = regResult = pDest->iSdst;
    if( srcTab>=0 ){
      for(i=0; i<nResultCol; i++){
        sqlite3VdbeAddOp3(v, OP_Column, srcTab, i, regResult+i);
        VdbeComment((v, "%s", p->pEList->a[i].zEName));
      }
    }else if( eDest!=SRT_Exists ){
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
      ExprList *pExtra = 0;
  #endif
      /* If the destination is an EXISTS(...) expression, the actual
      ** values returned by the SELECT are not required.
      */
      u8 ecelFlags;    /* "ecel" is an abbreviation of "ExprCodeExprList" */
      ExprList *pEList;
      if( eDest==SRT_Mem || eDest==SRT_Output || eDest==SRT_Coroutine ){
        ecelFlags = SQLITE_ECEL_DUP;
      }else{
        ecelFlags = 0;
      }
      if( pSort && hasDistinct==0 && eDest!=SRT_EphemTab && eDest!=SRT_Table ){
        /* For each expression in p->pEList that is a copy of an expression in
        ** the ORDER BY clause (pSort->pOrderBy), set the associated 
        ** iOrderByCol value to one more than the index of the ORDER BY 
        ** expression within the sort-key that pushOntoSorter() will generate.
        ** This allows the p->pEList field to be omitted from the sorted record,
        ** saving space and CPU cycles.  */
        ecelFlags |= (SQLITE_ECEL_OMITREF|SQLITE_ECEL_REF);
  
        for(i=pSort->nOBSat; i<pSort->pOrderBy->nExpr; i++){
          int j;
          if( (j = pSort->pOrderBy->a[i].u.x.iOrderByCol)>0 ){
            p->pEList->a[j-1].u.x.iOrderByCol = i+1-pSort->nOBSat;
          }
        }
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
        selectExprDefer(pParse, pSort, p->pEList, &pExtra);
        if( pExtra && pParse->db->mallocFailed==0 ){
          /* If there are any extra PK columns to add to the sorter records,
          ** allocate extra memory cells and adjust the OpenEphemeral 
          ** instruction to account for the larger records. This is only
          ** required if there are one or more WITHOUT ROWID tables with
          ** composite primary keys in the SortCtx.aDefer[] array.  */
          VdbeOp *pOp = sqlite3VdbeGetOp(v, pSort->addrSortIndex);
          pOp->p2 += (pExtra->nExpr - pSort->nDefer);
          pOp->p4.pKeyInfo->nAllField += (pExtra->nExpr - pSort->nDefer);
          pParse->nMem += pExtra->nExpr;
        }
  #endif
  
        /* Adjust nResultCol to account for columns that are omitted
        ** from the sorter by the optimizations in this branch */
        pEList = p->pEList;
        for(i=0; i<pEList->nExpr; i++){
          if( pEList->a[i].u.x.iOrderByCol>0
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
           || pEList->a[i].bSorterRef
  #endif
          ){
            nResultCol--;
            regOrig = 0;
          }
        }
  
        testcase( regOrig );
        testcase( eDest==SRT_Set );
        testcase( eDest==SRT_Mem );
        testcase( eDest==SRT_Coroutine );
        testcase( eDest==SRT_Output );
        assert( eDest==SRT_Set || eDest==SRT_Mem 
             || eDest==SRT_Coroutine || eDest==SRT_Output
             || eDest==SRT_Upfrom );
      }
      sRowLoadInfo.regResult = regResult;
      sRowLoadInfo.ecelFlags = ecelFlags;
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
      sRowLoadInfo.pExtra = pExtra;
      sRowLoadInfo.regExtraResult = regResult + nResultCol;
      if( pExtra ) nResultCol += pExtra->nExpr;
  #endif
      if( p->iLimit
       && (ecelFlags & SQLITE_ECEL_OMITREF)!=0 
       && nPrefixReg>0
      ){
        assert( pSort!=0 );
        assert( hasDistinct==0 );
        pSort->pDeferredRowLoad = &sRowLoadInfo;
        regOrig = 0;
      }else{
        innerLoopLoadRow(pParse, p, &sRowLoadInfo);
      }
    }
  
    /* If the DISTINCT keyword was present on the SELECT statement
    ** and this row has been seen before, then do not make this row
    ** part of the result.
    */
    if( hasDistinct ){
      int eType = pDistinct->eTnctType;
      int iTab = pDistinct->tabTnct;
      assert( nResultCol==p->pEList->nExpr );
      iTab = codeDistinct(pParse, eType, iTab, iContinue, p->pEList, regResult);
      fixDistinctOpenEph(pParse, eType, iTab, pDistinct->addrTnct);
      if( pSort==0 ){
        codeOffset(v, p->iOffset, iContinue);
      }
    }
  
    switch( eDest ){
      /* In this mode, write each query result to the key of the temporary
      ** table iParm.
      */
  #ifndef SQLITE_OMIT_COMPOUND_SELECT
      case SRT_Union: {
        int r1;
        r1 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nResultCol, r1);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, r1, regResult, nResultCol);
        sqlite3ReleaseTempReg(pParse, r1);
        break;
      }
  
      /* Construct a record from the query result, but instead of
      ** saving that record, use it as a key to delete elements from
      ** the temporary table iParm.
      */
      case SRT_Except: {
        sqlite3VdbeAddOp3(v, OP_IdxDelete, iParm, regResult, nResultCol);
        break;
      }
  #endif /* SQLITE_OMIT_COMPOUND_SELECT */
  
      /* Store the result as data using a unique key.
      */
      case SRT_Fifo:
      case SRT_DistFifo:
      case SRT_Table:
      case SRT_EphemTab: {
        int r1 = sqlite3GetTempRange(pParse, nPrefixReg+1);
        testcase( eDest==SRT_Table );
        testcase( eDest==SRT_EphemTab );
        testcase( eDest==SRT_Fifo );
        testcase( eDest==SRT_DistFifo );
        sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nResultCol, r1+nPrefixReg);
  #ifndef SQLITE_OMIT_CTE
        if( eDest==SRT_DistFifo ){
          /* If the destination is DistFifo, then cursor (iParm+1) is open
          ** on an ephemeral index. If the current row is already present
          ** in the index, do not write it to the output. If not, add the
          ** current row to the index and proceed with writing it to the
          ** output table as well.  */
          int addr = sqlite3VdbeCurrentAddr(v) + 4;
          sqlite3VdbeAddOp4Int(v, OP_Found, iParm+1, addr, r1, 0);
          VdbeCoverage(v);
          sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm+1, r1,regResult,nResultCol);
          assert( pSort==0 );
        }
  #endif
        if( pSort ){
          assert( regResult==regOrig );
          pushOntoSorter(pParse, pSort, p, r1+nPrefixReg, regOrig, 1, nPrefixReg);
        }else{
          int r2 = sqlite3GetTempReg(pParse);
          sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, r2);
          sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, r2);
          sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
          sqlite3ReleaseTempReg(pParse, r2);
        }
        sqlite3ReleaseTempRange(pParse, r1, nPrefixReg+1);
        break;
      }
  
      case SRT_Upfrom: {
        if( pSort ){
          pushOntoSorter(
              pParse, pSort, p, regResult, regOrig, nResultCol, nPrefixReg);
        }else{
          int i2 = pDest->iSDParm2;
          int r1 = sqlite3GetTempReg(pParse);
  
          /* If the UPDATE FROM join is an aggregate that matches no rows, it
          ** might still be trying to return one row, because that is what
          ** aggregates do.  Don't record that empty row in the output table. */
          sqlite3VdbeAddOp2(v, OP_IsNull, regResult, iBreak); VdbeCoverage(v);
  
          sqlite3VdbeAddOp3(v, OP_MakeRecord,
                            regResult+(i2<0), nResultCol-(i2<0), r1);
          if( i2<0 ){
            sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, regResult);
          }else{
            sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, r1, regResult, i2);
          }
        }
        break;
      }
  
  #ifndef SQLITE_OMIT_SUBQUERY
      /* If we are creating a set for an "expr IN (SELECT ...)" construct,
      ** then there should be a single item on the stack.  Write this
      ** item into the set table with bogus data.
      */
      case SRT_Set: {
        if( pSort ){
          /* At first glance you would think we could optimize out the
          ** ORDER BY in this case since the order of entries in the set
          ** does not matter.  But there might be a LIMIT clause, in which
          ** case the order does matter */
          pushOntoSorter(
              pParse, pSort, p, regResult, regOrig, nResultCol, nPrefixReg);
        }else{
          int r1 = sqlite3GetTempReg(pParse);
          assert( sqlite3Strlen30(pDest->zAffSdst)==nResultCol );
          sqlite3VdbeAddOp4(v, OP_MakeRecord, regResult, nResultCol, 
              r1, pDest->zAffSdst, nResultCol);
          sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, r1, regResult, nResultCol);
          sqlite3ReleaseTempReg(pParse, r1);
        }
        break;
      }
  
  
      /* If any row exist in the result set, record that fact and abort.
      */
      case SRT_Exists: {
        sqlite3VdbeAddOp2(v, OP_Integer, 1, iParm);
        /* The LIMIT clause will terminate the loop for us */
        break;
      }
  
      /* If this is a scalar select that is part of an expression, then
      ** store the results in the appropriate memory cell or array of 
      ** memory cells and break out of the scan loop.
      */
      case SRT_Mem: {
        if( pSort ){
          assert( nResultCol<=pDest->nSdst );
          pushOntoSorter(
              pParse, pSort, p, regResult, regOrig, nResultCol, nPrefixReg);
        }else{
          assert( nResultCol==pDest->nSdst );
          assert( regResult==iParm );
          /* The LIMIT clause will jump out of the loop for us */
        }
        break;
      }
  #endif /* #ifndef SQLITE_OMIT_SUBQUERY */
  
      case SRT_Coroutine:       /* Send data to a co-routine */
      case SRT_Output: {        /* Return the results */
        testcase( eDest==SRT_Coroutine );
        testcase( eDest==SRT_Output );
        if( pSort ){
          pushOntoSorter(pParse, pSort, p, regResult, regOrig, nResultCol,
                         nPrefixReg);
        }else if( eDest==SRT_Coroutine ){
          sqlite3VdbeAddOp1(v, OP_Yield, pDest->iSDParm);
        }else{
          sqlite3VdbeAddOp2(v, OP_ResultRow, regResult, nResultCol);
        }
        break;
      }
  
  #ifndef SQLITE_OMIT_CTE
      /* Write the results into a priority queue that is order according to
      ** pDest->pOrderBy (in pSO).  pDest->iSDParm (in iParm) is the cursor for an
      ** index with pSO->nExpr+2 columns.  Build a key using pSO for the first
      ** pSO->nExpr columns, then make sure all keys are unique by adding a
      ** final OP_Sequence column.  The last column is the record as a blob.
      */
      case SRT_DistQueue:
      case SRT_Queue: {
        int nKey;
        int r1, r2, r3;
        int addrTest = 0;
        ExprList *pSO;
        pSO = pDest->pOrderBy;
        assert( pSO );
        nKey = pSO->nExpr;
        r1 = sqlite3GetTempReg(pParse);
        r2 = sqlite3GetTempRange(pParse, nKey+2);
        r3 = r2+nKey+1;
        if( eDest==SRT_DistQueue ){
          /* If the destination is DistQueue, then cursor (iParm+1) is open
          ** on a second ephemeral index that holds all values every previously
          ** added to the queue. */
          addrTest = sqlite3VdbeAddOp4Int(v, OP_Found, iParm+1, 0, 
                                          regResult, nResultCol);
          VdbeCoverage(v);
        }
        sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nResultCol, r3);
        if( eDest==SRT_DistQueue ){
          sqlite3VdbeAddOp2(v, OP_IdxInsert, iParm+1, r3);
          sqlite3VdbeChangeP5(v, OPFLAG_USESEEKRESULT);
        }
        for(i=0; i<nKey; i++){
          sqlite3VdbeAddOp2(v, OP_SCopy,
                            regResult + pSO->a[i].u.x.iOrderByCol - 1,
                            r2+i);
        }
        sqlite3VdbeAddOp2(v, OP_Sequence, iParm, r2+nKey);
        sqlite3VdbeAddOp3(v, OP_MakeRecord, r2, nKey+2, r1);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, r1, r2, nKey+2);
        if( addrTest ) sqlite3VdbeJumpHere(v, addrTest);
        sqlite3ReleaseTempReg(pParse, r1);
        sqlite3ReleaseTempRange(pParse, r2, nKey+2);
        break;
      }
  #endif /* SQLITE_OMIT_CTE */
  
  
  
  #if !defined(SQLITE_OMIT_TRIGGER)
      /* Discard the results.  This is used for SELECT statements inside
      ** the body of a TRIGGER.  The purpose of such selects is to call
      ** user-defined functions that have side effects.  We do not care
      ** about the actual results of the select.
      */
      default: {
        assert( eDest==SRT_Discard );
        break;
      }
  #endif
    }
  
    /* Jump to the end of the loop if the LIMIT is reached.  Except, if
    ** there is a sorter, in which case the sorter has already limited
    ** the output for us.
    */
    if( pSort==0 && p->iLimit ){
      sqlite3VdbeAddOp2(v, OP_DecrJumpZero, p->iLimit, iBreak); VdbeCoverage(v);
    }
  }
  
  /*
  ** Allocate a KeyInfo object sufficient for an index of N key columns and
  ** X extra columns.
  */
  KeyInfo *sqlite3KeyInfoAlloc(sqlite3 *db, int N, int X){
    int nExtra = (N+X)*(sizeof(CollSeq*)+1) - sizeof(CollSeq*);
    KeyInfo *p = sqlite3DbMallocRawNN(db, sizeof(KeyInfo) + nExtra);
    if( p ){
      p->aSortFlags = (u8*)&p->aColl[N+X];
      p->nKeyField = (u16)N;
      p->nAllField = (u16)(N+X);
      p->enc = ENC(db);
      p->db = db;
      p->nRef = 1;
      memset(&p[1], 0, nExtra);
    }else{
      sqlite3OomFault(db);
    }
    return p;
  }
  
  /*
  ** Deallocate a KeyInfo object
  */
  void sqlite3KeyInfoUnref(KeyInfo *p){
    if( p ){
      assert( p->nRef>0 );
      p->nRef--;
      if( p->nRef==0 ) sqlite3DbFreeNN(p->db, p);
    }
  }
  
  /*
  ** Make a new pointer to a KeyInfo object
  */
  KeyInfo *sqlite3KeyInfoRef(KeyInfo *p){
    if( p ){
      assert( p->nRef>0 );
      p->nRef++;
    }
    return p;
  }
  
  #ifdef SQLITE_DEBUG
  /*
  ** Return TRUE if a KeyInfo object can be change.  The KeyInfo object
  ** can only be changed if this is just a single reference to the object.
  **
  ** This routine is used only inside of assert() statements.
  */
  int sqlite3KeyInfoIsWriteable(KeyInfo *p){ return p->nRef==1; }
  #endif /* SQLITE_DEBUG */
  
  /*
  ** Given an expression list, generate a KeyInfo structure that records
  ** the collating sequence for each expression in that expression list.
  **
  ** If the ExprList is an ORDER BY or GROUP BY clause then the resulting
  ** KeyInfo structure is appropriate for initializing a virtual index to
  ** implement that clause.  If the ExprList is the result set of a SELECT
  ** then the KeyInfo structure is appropriate for initializing a virtual
  ** index to implement a DISTINCT test.
  **
  ** Space to hold the KeyInfo structure is obtained from malloc.  The calling
  ** function is responsible for seeing that this structure is eventually
  ** freed.
  */
  KeyInfo *sqlite3KeyInfoFromExprList(
    Parse *pParse,       /* Parsing context */
    ExprList *pList,     /* Form the KeyInfo object from this ExprList */
    int iStart,          /* Begin with this column of pList */
    int nExtra           /* Add this many extra columns to the end */
  ){
    int nExpr;
    KeyInfo *pInfo;
    struct ExprList_item *pItem;
    sqlite3 *db = pParse->db;
    int i;
  
    nExpr = pList->nExpr;
    pInfo = sqlite3KeyInfoAlloc(db, nExpr-iStart, nExtra+1);
    if( pInfo ){
      assert( sqlite3KeyInfoIsWriteable(pInfo) );
      for(i=iStart, pItem=pList->a+iStart; i<nExpr; i++, pItem++){
        pInfo->aColl[i-iStart] = sqlite3ExprNNCollSeq(pParse, pItem->pExpr);
        pInfo->aSortFlags[i-iStart] = pItem->sortFlags;
      }
    }
    return pInfo;
  }
  
  /*
  ** Name of the connection operator, used for error messages.
  */
  const char *sqlite3SelectOpName(int id){
    char *z;
    switch( id ){
      case TK_ALL:       z = "UNION ALL";   break;
      case TK_INTERSECT: z = "INTERSECT";   break;
      case TK_EXCEPT:    z = "EXCEPT";      break;
      default:           z = "UNION";       break;
    }
    return z;
  }
  
  #ifndef SQLITE_OMIT_EXPLAIN
  /*
  ** Unless an "EXPLAIN QUERY PLAN" command is being processed, this function
  ** is a no-op. Otherwise, it adds a single row of output to the EQP result,
  ** where the caption is of the form:
  **
  **   "USE TEMP B-TREE FOR xxx"
  **
  ** where xxx is one of "DISTINCT", "ORDER BY" or "GROUP BY". Exactly which
  ** is determined by the zUsage argument.
  */
  static void explainTempTable(Parse *pParse, const char *zUsage){
    ExplainQueryPlan((pParse, 0, "USE TEMP B-TREE FOR %s", zUsage));
  }
  
  /*
  ** Assign expression b to lvalue a. A second, no-op, version of this macro
  ** is provided when SQLITE_OMIT_EXPLAIN is defined. This allows the code
  ** in sqlite3Select() to assign values to structure member variables that
  ** only exist if SQLITE_OMIT_EXPLAIN is not defined without polluting the
  ** code with #ifndef directives.
  */
  # define explainSetInteger(a, b) a = b
  
  #else
  /* No-op versions of the explainXXX() functions and macros. */
  # define explainTempTable(y,z)
  # define explainSetInteger(y,z)
  #endif
  
  
  /*
  ** If the inner loop was generated using a non-null pOrderBy argument,
  ** then the results were placed in a sorter.  After the loop is terminated
  ** we need to run the sorter and output the results.  The following
  ** routine generates the code needed to do that.
  */
  static void generateSortTail(
    Parse *pParse,    /* Parsing context */
    Select *p,        /* The SELECT statement */
    SortCtx *pSort,   /* Information on the ORDER BY clause */
    int nColumn,      /* Number of columns of data */
    SelectDest *pDest /* Write the sorted results here */
  ){
    Vdbe *v = pParse->pVdbe;                     /* The prepared statement */
    int addrBreak = pSort->labelDone;            /* Jump here to exit loop */
    int addrContinue = sqlite3VdbeMakeLabel(pParse);/* Jump here for next cycle */
    int addr;                       /* Top of output loop. Jump for Next. */
    int addrOnce = 0;
    int iTab;
    ExprList *pOrderBy = pSort->pOrderBy;
    int eDest = pDest->eDest;
    int iParm = pDest->iSDParm;
    int regRow;
    int regRowid;
    int iCol;
    int nKey;                       /* Number of key columns in sorter record */
    int iSortTab;                   /* Sorter cursor to read from */
    int i;
    int bSeq;                       /* True if sorter record includes seq. no. */
    int nRefKey = 0;
    struct ExprList_item *aOutEx = p->pEList->a;
  
    assert( addrBreak<0 );
    if( pSort->labelBkOut ){
      sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
      sqlite3VdbeGoto(v, addrBreak);
      sqlite3VdbeResolveLabel(v, pSort->labelBkOut);
    }
  
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
    /* Open any cursors needed for sorter-reference expressions */
    for(i=0; i<pSort->nDefer; i++){
      Table *pTab = pSort->aDefer[i].pTab;
      int iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
      sqlite3OpenTable(pParse, pSort->aDefer[i].iCsr, iDb, pTab, OP_OpenRead);
      nRefKey = MAX(nRefKey, pSort->aDefer[i].nKey);
    }
  #endif
  
    iTab = pSort->iECursor;
    if( eDest==SRT_Output || eDest==SRT_Coroutine || eDest==SRT_Mem ){
      regRowid = 0;
      regRow = pDest->iSdst;
    }else{
      regRowid = sqlite3GetTempReg(pParse);
      if( eDest==SRT_EphemTab || eDest==SRT_Table ){
        regRow = sqlite3GetTempReg(pParse);
        nColumn = 0;
      }else{
        regRow = sqlite3GetTempRange(pParse, nColumn);
      }
    }
    nKey = pOrderBy->nExpr - pSort->nOBSat;
    if( pSort->sortFlags & SORTFLAG_UseSorter ){
      int regSortOut = ++pParse->nMem;
      iSortTab = pParse->nTab++;
      if( pSort->labelBkOut ){
        addrOnce = sqlite3VdbeAddOp0(v, OP_Once); VdbeCoverage(v);
      }
      sqlite3VdbeAddOp3(v, OP_OpenPseudo, iSortTab, regSortOut, 
          nKey+1+nColumn+nRefKey);
      if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
      addr = 1 + sqlite3VdbeAddOp2(v, OP_SorterSort, iTab, addrBreak);
      VdbeCoverage(v);
      codeOffset(v, p->iOffset, addrContinue);
      sqlite3VdbeAddOp3(v, OP_SorterData, iTab, regSortOut, iSortTab);
      bSeq = 0;
    }else{
      addr = 1 + sqlite3VdbeAddOp2(v, OP_Sort, iTab, addrBreak); VdbeCoverage(v);
      codeOffset(v, p->iOffset, addrContinue);
      iSortTab = iTab;
      bSeq = 1;
    }
    for(i=0, iCol=nKey+bSeq-1; i<nColumn; i++){
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
      if( aOutEx[i].bSorterRef ) continue;
  #endif
      if( aOutEx[i].u.x.iOrderByCol==0 ) iCol++;
    }
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
    if( pSort->nDefer ){
      int iKey = iCol+1;
      int regKey = sqlite3GetTempRange(pParse, nRefKey);
  
      for(i=0; i<pSort->nDefer; i++){
        int iCsr = pSort->aDefer[i].iCsr;
        Table *pTab = pSort->aDefer[i].pTab;
        int nKey = pSort->aDefer[i].nKey;
  
        sqlite3VdbeAddOp1(v, OP_NullRow, iCsr);
        if( HasRowid(pTab) ){
          sqlite3VdbeAddOp3(v, OP_Column, iSortTab, iKey++, regKey);
          sqlite3VdbeAddOp3(v, OP_SeekRowid, iCsr, 
              sqlite3VdbeCurrentAddr(v)+1, regKey);
        }else{
          int k;
          int iJmp;
          assert( sqlite3PrimaryKeyIndex(pTab)->nKeyCol==nKey );
          for(k=0; k<nKey; k++){
            sqlite3VdbeAddOp3(v, OP_Column, iSortTab, iKey++, regKey+k);
          }
          iJmp = sqlite3VdbeCurrentAddr(v);
          sqlite3VdbeAddOp4Int(v, OP_SeekGE, iCsr, iJmp+2, regKey, nKey);
          sqlite3VdbeAddOp4Int(v, OP_IdxLE, iCsr, iJmp+3, regKey, nKey);
          sqlite3VdbeAddOp1(v, OP_NullRow, iCsr);
        }
      }
      sqlite3ReleaseTempRange(pParse, regKey, nRefKey);
    }
  #endif
    for(i=nColumn-1; i>=0; i--){
  #ifdef SQLITE_ENABLE_SORTER_REFERENCES
      if( aOutEx[i].bSorterRef ){
        sqlite3ExprCode(pParse, aOutEx[i].pExpr, regRow+i);
      }else
  #endif
      {
        int iRead;
        if( aOutEx[i].u.x.iOrderByCol ){
          iRead = aOutEx[i].u.x.iOrderByCol-1;
        }else{
          iRead = iCol--;
        }
        sqlite3VdbeAddOp3(v, OP_Column, iSortTab, iRead, regRow+i);
        VdbeComment((v, "%s", aOutEx[i].zEName));
      }
    }
    switch( eDest ){
      case SRT_Table:
      case SRT_EphemTab: {
        sqlite3VdbeAddOp3(v, OP_Column, iSortTab, nKey+bSeq, regRow);
        sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, regRowid);
        sqlite3VdbeAddOp3(v, OP_Insert, iParm, regRow, regRowid);
        sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
        break;
      }
  #ifndef SQLITE_OMIT_SUBQUERY
      case SRT_Set: {
        assert( nColumn==sqlite3Strlen30(pDest->zAffSdst) );
        sqlite3VdbeAddOp4(v, OP_MakeRecord, regRow, nColumn, regRowid,
                          pDest->zAffSdst, nColumn);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, regRowid, regRow, nColumn);
        break;
      }
      case SRT_Mem: {
        /* The LIMIT clause will terminate the loop for us */
        break;
      }
  #endif
      case SRT_Upfrom: {
        int i2 = pDest->iSDParm2;
        int r1 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp3(v, OP_MakeRecord,regRow+(i2<0),nColumn-(i2<0),r1);
        if( i2<0 ){
          sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, regRow);
        }else{
          sqlite3VdbeAddOp4Int(v, OP_IdxInsert, iParm, r1, regRow, i2);
        }
        break;
      }
      default: {
        assert( eDest==SRT_Output || eDest==SRT_Coroutine ); 
        testcase( eDest==SRT_Output );
        testcase( eDest==SRT_Coroutine );
        if( eDest==SRT_Output ){
          sqlite3VdbeAddOp2(v, OP_ResultRow, pDest->iSdst, nColumn);
        }else{
          sqlite3VdbeAddOp1(v, OP_Yield, pDest->iSDParm);
        }
        break;
      }
    }
    if( regRowid ){
      if( eDest==SRT_Set ){
        sqlite3ReleaseTempRange(pParse, regRow, nColumn);
      }else{
        sqlite3ReleaseTempReg(pParse, regRow);
      }
      sqlite3ReleaseTempReg(pParse, regRowid);
    }
    /* The bottom of the loop
    */
    sqlite3VdbeResolveLabel(v, addrContinue);
    if( pSort->sortFlags & SORTFLAG_UseSorter ){
      sqlite3VdbeAddOp2(v, OP_SorterNext, iTab, addr); VdbeCoverage(v);
    }else{
      sqlite3VdbeAddOp2(v, OP_Next, iTab, addr); VdbeCoverage(v);
    }
    if( pSort->regReturn ) sqlite3VdbeAddOp1(v, OP_Return, pSort->regReturn);
    sqlite3VdbeResolveLabel(v, addrBreak);
  }
  
  /*
  ** Return a pointer to a string containing the 'declaration type' of the
  ** expression pExpr. The string may be treated as static by the caller.
  **
  ** Also try to estimate the size of the returned value and return that
  ** result in *pEstWidth.
  **
  ** The declaration type is the exact datatype definition extracted from the
  ** original CREATE TABLE statement if the expression is a column. The
  ** declaration type for a ROWID field is INTEGER. Exactly when an expression
  ** is considered a column can be complex in the presence of subqueries. The
  ** result-set expression in all of the following SELECT statements is 
  ** considered a column by this function.
  **
  **   SELECT col FROM tbl;
  **   SELECT (SELECT col FROM tbl;
  **   SELECT (SELECT col FROM tbl);
  **   SELECT abc FROM (SELECT col AS abc FROM tbl);
  ** 
  ** The declaration type for any expression other than a column is NULL.
  **
  ** This routine has either 3 or 6 parameters depending on whether or not
  ** the SQLITE_ENABLE_COLUMN_METADATA compile-time option is used.
  */
  #ifdef SQLITE_ENABLE_COLUMN_METADATA
  # define columnType(A,B,C,D,E) columnTypeImpl(A,B,C,D,E)
  #else /* if !defined(SQLITE_ENABLE_COLUMN_METADATA) */
  # define columnType(A,B,C,D,E) columnTypeImpl(A,B)
  #endif
  static const char *columnTypeImpl(
    NameContext *pNC, 
  #ifndef SQLITE_ENABLE_COLUMN_METADATA
    Expr *pExpr
  #else
    Expr *pExpr,
    const char **pzOrigDb,
    const char **pzOrigTab,
    const char **pzOrigCol
  #endif
  ){
    char const *zType = 0;
    int j;
  #ifdef SQLITE_ENABLE_COLUMN_METADATA
    char const *zOrigDb = 0;
    char const *zOrigTab = 0;
    char const *zOrigCol = 0;
  #endif
  
    assert( pExpr!=0 );
    assert( pNC->pSrcList!=0 );
    switch( pExpr->op ){
      case TK_COLUMN: {
        /* The expression is a column. Locate the table the column is being
        ** extracted from in NameContext.pSrcList. This table may be real
        ** database table or a subquery.
        */
        Table *pTab = 0;            /* Table structure column is extracted from */
        Select *pS = 0;             /* Select the column is extracted from */
        int iCol = pExpr->iColumn;  /* Index of column in pTab */
        while( pNC && !pTab ){
          SrcList *pTabList = pNC->pSrcList;
          for(j=0;j<pTabList->nSrc && pTabList->a[j].iCursor!=pExpr->iTable;j++);
          if( j<pTabList->nSrc ){
            pTab = pTabList->a[j].pTab;
            pS = pTabList->a[j].pSelect;
          }else{
            pNC = pNC->pNext;
          }
        }
  
        if( pTab==0 ){
          /* At one time, code such as "SELECT new.x" within a trigger would
          ** cause this condition to run.  Since then, we have restructured how
          ** trigger code is generated and so this condition is no longer 
          ** possible. However, it can still be true for statements like
          ** the following:
          **
          **   CREATE TABLE t1(col INTEGER);
          **   SELECT (SELECT t1.col) FROM FROM t1;
          **
          ** when columnType() is called on the expression "t1.col" in the 
          ** sub-select. In this case, set the column type to NULL, even
          ** though it should really be "INTEGER".
          **
          ** This is not a problem, as the column type of "t1.col" is never
          ** used. When columnType() is called on the expression 
          ** "(SELECT t1.col)", the correct type is returned (see the TK_SELECT
          ** branch below.  */
          break;
        }
  
        assert( pTab && pExpr->y.pTab==pTab );
        if( pS ){
          /* The "table" is actually a sub-select or a view in the FROM clause
          ** of the SELECT statement. Return the declaration type and origin
          ** data for the result-set column of the sub-select.
          */
          if( iCol<pS->pEList->nExpr
  #ifdef SQLITE_ALLOW_ROWID_IN_VIEW
           && iCol>=0
  #else
           && ALWAYS(iCol>=0)
  #endif
          ){ 
            /* If iCol is less than zero, then the expression requests the
            ** rowid of the sub-select or view. This expression is legal (see 
            ** test case misc2.2.2) - it always evaluates to NULL.
            */
            NameContext sNC;
            Expr *p = pS->pEList->a[iCol].pExpr;
            sNC.pSrcList = pS->pSrc;
            sNC.pNext = pNC;
            sNC.pParse = pNC->pParse;
            zType = columnType(&sNC, p,&zOrigDb,&zOrigTab,&zOrigCol); 
          }
        }else{
          /* A real table or a CTE table */
          assert( !pS );
  #ifdef SQLITE_ENABLE_COLUMN_METADATA
          if( iCol<0 ) iCol = pTab->iPKey;
          assert( iCol==XN_ROWID || (iCol>=0 && iCol<pTab->nCol) );
          if( iCol<0 ){
            zType = "INTEGER";
            zOrigCol = "rowid";
          }else{
            zOrigCol = pTab->aCol[iCol].zName;
            zType = sqlite3ColumnType(&pTab->aCol[iCol],0);
          }
          zOrigTab = pTab->zName;
          if( pNC->pParse && pTab->pSchema ){
            int iDb = sqlite3SchemaToIndex(pNC->pParse->db, pTab->pSchema);
            zOrigDb = pNC->pParse->db->aDb[iDb].zDbSName;
          }
  #else
          assert( iCol==XN_ROWID || (iCol>=0 && iCol<pTab->nCol) );
          if( iCol<0 ){
            zType = "INTEGER";
          }else{
            zType = sqlite3ColumnType(&pTab->aCol[iCol],0);
          }
  #endif
        }
        break;
      }
  #ifndef SQLITE_OMIT_SUBQUERY
      case TK_SELECT: {
        /* The expression is a sub-select. Return the declaration type and
        ** origin info for the single column in the result set of the SELECT
        ** statement.
        */
        NameContext sNC;
        Select *pS = pExpr->x.pSelect;
        Expr *p = pS->pEList->a[0].pExpr;
        assert( ExprHasProperty(pExpr, EP_xIsSelect) );
        sNC.pSrcList = pS->pSrc;
        sNC.pNext = pNC;
        sNC.pParse = pNC->pParse;
        zType = columnType(&sNC, p, &zOrigDb, &zOrigTab, &zOrigCol); 
        break;
      }
  #endif
    }
  
  #ifdef SQLITE_ENABLE_COLUMN_METADATA  
    if( pzOrigDb ){
      assert( pzOrigTab && pzOrigCol );
      *pzOrigDb = zOrigDb;
      *pzOrigTab = zOrigTab;
      *pzOrigCol = zOrigCol;
    }
  #endif
    return zType;
  }
  
  /*
  ** Generate code that will tell the VDBE the declaration types of columns
  ** in the result set.
  */
  static void generateColumnTypes(
    Parse *pParse,      /* Parser context */
    SrcList *pTabList,  /* List of tables */
    ExprList *pEList    /* Expressions defining the result set */
  ){
  #ifndef SQLITE_OMIT_DECLTYPE
    Vdbe *v = pParse->pVdbe;
    int i;
    NameContext sNC;
    sNC.pSrcList = pTabList;
    sNC.pParse = pParse;
    sNC.pNext = 0;
    for(i=0; i<pEList->nExpr; i++){
      Expr *p = pEList->a[i].pExpr;
      const char *zType;
  #ifdef SQLITE_ENABLE_COLUMN_METADATA
      const char *zOrigDb = 0;
      const char *zOrigTab = 0;
      const char *zOrigCol = 0;
      zType = columnType(&sNC, p, &zOrigDb, &zOrigTab, &zOrigCol);
  
      /* The vdbe must make its own copy of the column-type and other 
      ** column specific strings, in case the schema is reset before this
      ** virtual machine is deleted.
      */
      sqlite3VdbeSetColName(v, i, COLNAME_DATABASE, zOrigDb, SQLITE_TRANSIENT);
      sqlite3VdbeSetColName(v, i, COLNAME_TABLE, zOrigTab, SQLITE_TRANSIENT);
      sqlite3VdbeSetColName(v, i, COLNAME_COLUMN, zOrigCol, SQLITE_TRANSIENT);
  #else
      zType = columnType(&sNC, p, 0, 0, 0);
  #endif
      sqlite3VdbeSetColName(v, i, COLNAME_DECLTYPE, zType, SQLITE_TRANSIENT);
    }
  #endif /* !defined(SQLITE_OMIT_DECLTYPE) */
  }
  
  
  /*
  ** Compute the column names for a SELECT statement.
  **
  ** The only guarantee that SQLite makes about column names is that if the
  ** column has an AS clause assigning it a name, that will be the name used.
  ** That is the only documented guarantee.  However, countless applications
  ** developed over the years have made baseless assumptions about column names
  ** and will break if those assumptions changes.  Hence, use extreme caution
  ** when modifying this routine to avoid breaking legacy.
  **
  ** See Also: sqlite3ColumnsFromExprList()
  **
  ** The PRAGMA short_column_names and PRAGMA full_column_names settings are
  ** deprecated.  The default setting is short=ON, full=OFF.  99.9% of all
  ** applications should operate this way.  Nevertheless, we need to support the
  ** other modes for legacy:
  **
  **    short=OFF, full=OFF:      Column name is the text of the expression has it
  **                              originally appears in the SELECT statement.  In
  **                              other words, the zSpan of the result expression.
  **
  **    short=ON, full=OFF:       (This is the default setting).  If the result
  **                              refers directly to a table column, then the
  **                              result column name is just the table column
  **                              name: COLUMN.  Otherwise use zSpan.
  **
  **    full=ON, short=ANY:       If the result refers directly to a table column,
  **                              then the result column name with the table name
  **                              prefix, ex: TABLE.COLUMN.  Otherwise use zSpan.
  */
  void sqlite3GenerateColumnNames(
    Parse *pParse,      /* Parser context */
    Select *pSelect     /* Generate column names for this SELECT statement */
  ){
    Vdbe *v = pParse->pVdbe;
    int i;
    Table *pTab;
    SrcList *pTabList;
    ExprList *pEList;
    sqlite3 *db = pParse->db;
    int fullName;    /* TABLE.COLUMN if no AS clause and is a direct table ref */
    int srcName;     /* COLUMN or TABLE.COLUMN if no AS clause and is direct */
  
  #ifndef SQLITE_OMIT_EXPLAIN
    /* If this is an EXPLAIN, skip this step */
    if( pParse->explain ){
      return;
    }
  #endif
  
    if( pParse->colNamesSet ) return;
    /* Column names are determined by the left-most term of a compound select */
    while( pSelect->pPrior ) pSelect = pSelect->pPrior;
    SELECTTRACE(1,pParse,pSelect,("generating column names\n"));
    pTabList = pSelect->pSrc;
    pEList = pSelect->pEList;
    assert( v!=0 );
    assert( pTabList!=0 );
    pParse->colNamesSet = 1;
    fullName = (db->flags & SQLITE_FullColNames)!=0;
    srcName = (db->flags & SQLITE_ShortColNames)!=0 || fullName;
    sqlite3VdbeSetNumCols(v, pEList->nExpr);
    for(i=0; i<pEList->nExpr; i++){
      Expr *p = pEList->a[i].pExpr;
  
      assert( p!=0 );
      assert( p->op!=TK_AGG_COLUMN );  /* Agg processing has not run yet */
      assert( p->op!=TK_COLUMN || p->y.pTab!=0 ); /* Covering idx not yet coded */
      if( pEList->a[i].zEName && pEList->a[i].eEName==ENAME_NAME ){
        /* An AS clause always takes first priority */
        char *zName = pEList->a[i].zEName;
        sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_TRANSIENT);
      }else if( srcName && p->op==TK_COLUMN ){
        char *zCol;
        int iCol = p->iColumn;
        pTab = p->y.pTab;
        assert( pTab!=0 );
        if( iCol<0 ) iCol = pTab->iPKey;
        assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );
        if( iCol<0 ){
          zCol = "rowid";
        }else{
          zCol = pTab->aCol[iCol].zName;
        }
        if( fullName ){
          char *zName = 0;
          zName = sqlite3MPrintf(db, "%s.%s", pTab->zName, zCol);
          sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, SQLITE_DYNAMIC);
        }else{
          sqlite3VdbeSetColName(v, i, COLNAME_NAME, zCol, SQLITE_TRANSIENT);
        }
      }else{
        const char *z = pEList->a[i].zEName;
        z = z==0 ? sqlite3MPrintf(db, "column%d", i+1) : sqlite3DbStrDup(db, z);
        sqlite3VdbeSetColName(v, i, COLNAME_NAME, z, SQLITE_DYNAMIC);
      }
    }
    generateColumnTypes(pParse, pTabList, pEList);
  }
  
  /*
  ** Given an expression list (which is really the list of expressions
  ** that form the result set of a SELECT statement) compute appropriate
  ** column names for a table that would hold the expression list.
  **
  ** All column names will be unique.
  **
  ** Only the column names are computed.  Column.zType, Column.zColl,
  ** and other fields of Column are zeroed.
  **
  ** Return SQLITE_OK on success.  If a memory allocation error occurs,
  ** store NULL in *paCol and 0 in *pnCol and return SQLITE_NOMEM.
  **
  ** The only guarantee that SQLite makes about column names is that if the
  ** column has an AS clause assigning it a name, that will be the name used.
  ** That is the only documented guarantee.  However, countless applications
  ** developed over the years have made baseless assumptions about column names
  ** and will break if those assumptions changes.  Hence, use extreme caution
  ** when modifying this routine to avoid breaking legacy.
  **
  ** See Also: sqlite3GenerateColumnNames()
  */
  int sqlite3ColumnsFromExprList(
    Parse *pParse,          /* Parsing context */
    ExprList *pEList,       /* Expr list from which to derive column names */
    i16 *pnCol,             /* Write the number of columns here */
    Column **paCol          /* Write the new column list here */
  ){
    sqlite3 *db = pParse->db;   /* Database connection */
    int i, j;                   /* Loop counters */
    u32 cnt;                    /* Index added to make the name unique */
    Column *aCol, *pCol;        /* For looping over result columns */
    int nCol;                   /* Number of columns in the result set */
    char *zName;                /* Column name */
    int nName;                  /* Size of name in zName[] */
    Hash ht;                    /* Hash table of column names */
    Table *pTab;
  
    sqlite3HashInit(&ht);
    if( pEList ){
      nCol = pEList->nExpr;
      aCol = sqlite3DbMallocZero(db, sizeof(aCol[0])*nCol);
      testcase( aCol==0 );
      if( NEVER(nCol>32767) ) nCol = 32767;
    }else{
      nCol = 0;
      aCol = 0;
    }
    assert( nCol==(i16)nCol );
    *pnCol = nCol;
    *paCol = aCol;
  
    for(i=0, pCol=aCol; i<nCol && !db->mallocFailed; i++, pCol++){
      /* Get an appropriate name for the column
      */
      if( (zName = pEList->a[i].zEName)!=0 && pEList->a[i].eEName==ENAME_NAME ){
        /* If the column contains an "AS <name>" phrase, use <name> as the name */
      }else{
        Expr *pColExpr = sqlite3ExprSkipCollateAndLikely(pEList->a[i].pExpr);
        while( ALWAYS(pColExpr!=0) && pColExpr->op==TK_DOT ){
          pColExpr = pColExpr->pRight;
          assert( pColExpr!=0 );
        }
        if( pColExpr->op==TK_COLUMN && (pTab = pColExpr->y.pTab)!=0 ){
          /* For columns use the column name name */
          int iCol = pColExpr->iColumn;
          if( iCol<0 ) iCol = pTab->iPKey;
          zName = iCol>=0 ? pTab->aCol[iCol].zName : "rowid";
        }else if( pColExpr->op==TK_ID ){
          assert( !ExprHasProperty(pColExpr, EP_IntValue) );
          zName = pColExpr->u.zToken;
        }else{
          /* Use the original text of the column expression as its name */
          zName = pEList->a[i].zEName;
        }
      }
      if( zName && !sqlite3IsTrueOrFalse(zName) ){
        zName = sqlite3DbStrDup(db, zName);
      }else{
        zName = sqlite3MPrintf(db,"column%d",i+1);
      }
  
      /* Make sure the column name is unique.  If the name is not unique,
      ** append an integer to the name so that it becomes unique.
      */
      cnt = 0;
      while( zName && sqlite3HashFind(&ht, zName)!=0 ){
        nName = sqlite3Strlen30(zName);
        if( nName>0 ){
          for(j=nName-1; j>0 && sqlite3Isdigit(zName[j]); j--){}
          if( zName[j]==':' ) nName = j;
        }
        zName = sqlite3MPrintf(db, "%.*z:%u", nName, zName, ++cnt);
        if( cnt>3 ) sqlite3_randomness(sizeof(cnt), &cnt);
      }
      pCol->zName = zName;
      pCol->hName = sqlite3StrIHash(zName);
      sqlite3ColumnPropertiesFromName(0, pCol);
      if( zName && sqlite3HashInsert(&ht, zName, pCol)==pCol ){
        sqlite3OomFault(db);
      }
    }
    sqlite3HashClear(&ht);
    if( db->mallocFailed ){
      for(j=0; j<i; j++){
        sqlite3DbFree(db, aCol[j].zName);
      }
      sqlite3DbFree(db, aCol);
      *paCol = 0;
      *pnCol = 0;
      return SQLITE_NOMEM_BKPT;
    }
    return SQLITE_OK;
  }
  
  /*
  ** Add type and collation information to a column list based on
  ** a SELECT statement.
  ** 
  ** The column list presumably came from selectColumnNamesFromExprList().
  ** The column list has only names, not types or collations.  This
  ** routine goes through and adds the types and collations.
  **
  ** This routine requires that all identifiers in the SELECT
  ** statement be resolved.
  */
  void sqlite3SelectAddColumnTypeAndCollation(
    Parse *pParse,        /* Parsing contexts */
    Table *pTab,          /* Add column type information to this table */
    Select *pSelect,      /* SELECT used to determine types and collations */
    char aff              /* Default affinity for columns */
  ){
    sqlite3 *db = pParse->db;
    NameContext sNC;
    Column *pCol;
    CollSeq *pColl;
    int i;
    Expr *p;
    struct ExprList_item *a;
  
    assert( pSelect!=0 );
    assert( (pSelect->selFlags & SF_Resolved)!=0 );
    assert( pTab->nCol==pSelect->pEList->nExpr || db->mallocFailed );
    if( db->mallocFailed ) return;
    memset(&sNC, 0, sizeof(sNC));
    sNC.pSrcList = pSelect->pSrc;
    a = pSelect->pEList->a;
    for(i=0, pCol=pTab->aCol; i<pTab->nCol; i++, pCol++){
      const char *zType;
      int n, m;
      pTab->tabFlags |= (pCol->colFlags & COLFLAG_NOINSERT);
      p = a[i].pExpr;
      zType = columnType(&sNC, p, 0, 0, 0);
      /* pCol->szEst = ... // Column size est for SELECT tables never used */
      pCol->affinity = sqlite3ExprAffinity(p);
      if( zType ){
        m = sqlite3Strlen30(zType);
        n = sqlite3Strlen30(pCol->zName);
        pCol->zName = sqlite3DbReallocOrFree(db, pCol->zName, n+m+2);
        if( pCol->zName ){
          memcpy(&pCol->zName[n+1], zType, m+1);
          pCol->colFlags |= COLFLAG_HASTYPE;
        }
      }
      if( pCol->affinity<=SQLITE_AFF_NONE ) pCol->affinity = aff;
      pColl = sqlite3ExprCollSeq(pParse, p);
      if( pColl && pCol->zColl==0 ){
        pCol->zColl = sqlite3DbStrDup(db, pColl->zName);
      }
    }
    pTab->szTabRow = 1; /* Any non-zero value works */
  }
  
  /*
  ** Given a SELECT statement, generate a Table structure that describes
  ** the result set of that SELECT.
  */
  Table *sqlite3ResultSetOfSelect(Parse *pParse, Select *pSelect, char aff){
    Table *pTab;
    sqlite3 *db = pParse->db;
    u64 savedFlags;
  
    savedFlags = db->flags;
    db->flags &= ~(u64)SQLITE_FullColNames;
    db->flags |= SQLITE_ShortColNames;
    sqlite3SelectPrep(pParse, pSelect, 0);
    db->flags = savedFlags;
    if( pParse->nErr ) return 0;
    while( pSelect->pPrior ) pSelect = pSelect->pPrior;
    pTab = sqlite3DbMallocZero(db, sizeof(Table) );
    if( pTab==0 ){
      return 0;
    }
    pTab->nTabRef = 1;
    pTab->zName = 0;
    pTab->nRowLogEst = 200; assert( 200==sqlite3LogEst(1048576) );
    sqlite3ColumnsFromExprList(pParse, pSelect->pEList, &pTab->nCol, &pTab->aCol);
    sqlite3SelectAddColumnTypeAndCollation(pParse, pTab, pSelect, aff);
    pTab->iPKey = -1;
    if( db->mallocFailed ){
      sqlite3DeleteTable(db, pTab);
      return 0;
    }
    return pTab;
  }
  
  /*
  ** Get a VDBE for the given parser context.  Create a new one if necessary.
  ** If an error occurs, return NULL and leave a message in pParse.
  */
  Vdbe *sqlite3GetVdbe(Parse *pParse){
    if( pParse->pVdbe ){
      return pParse->pVdbe;
    }
    if( pParse->pToplevel==0
     && OptimizationEnabled(pParse->db,SQLITE_FactorOutConst)
    ){
      pParse->okConstFactor = 1;
    }
    return sqlite3VdbeCreate(pParse);
  }
  
  
  /*
  ** Compute the iLimit and iOffset fields of the SELECT based on the
  ** pLimit expressions.  pLimit->pLeft and pLimit->pRight hold the expressions
  ** that appear in the original SQL statement after the LIMIT and OFFSET
  ** keywords.  Or NULL if those keywords are omitted. iLimit and iOffset 
  ** are the integer memory register numbers for counters used to compute 
  ** the limit and offset.  If there is no limit and/or offset, then 
  ** iLimit and iOffset are negative.
  **
  ** This routine changes the values of iLimit and iOffset only if
  ** a limit or offset is defined by pLimit->pLeft and pLimit->pRight.  iLimit
  ** and iOffset should have been preset to appropriate default values (zero)
  ** prior to calling this routine.
  **
  ** The iOffset register (if it exists) is initialized to the value
  ** of the OFFSET.  The iLimit register is initialized to LIMIT.  Register
  ** iOffset+1 is initialized to LIMIT+OFFSET.
  **
  ** Only if pLimit->pLeft!=0 do the limit registers get
  ** redefined.  The UNION ALL operator uses this property to force
  ** the reuse of the same limit and offset registers across multiple
  ** SELECT statements.
  */
  static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
    Vdbe *v = 0;
    int iLimit = 0;
    int iOffset;
    int n;
    Expr *pLimit = p->pLimit;
  
    if( p->iLimit ) return;
  
    /* 
    ** "LIMIT -1" always shows all rows.  There is some
    ** controversy about what the correct behavior should be.
    ** The current implementation interprets "LIMIT 0" to mean
    ** no rows.
    */
    if( pLimit ){
      assert( pLimit->op==TK_LIMIT );
      assert( pLimit->pLeft!=0 );
      p->iLimit = iLimit = ++pParse->nMem;
      v = sqlite3GetVdbe(pParse);
      assert( v!=0 );
      if( sqlite3ExprIsInteger(pLimit->pLeft, &n) ){
        sqlite3VdbeAddOp2(v, OP_Integer, n, iLimit);
        VdbeComment((v, "LIMIT counter"));
        if( n==0 ){
          sqlite3VdbeGoto(v, iBreak);
        }else if( n>=0 && p->nSelectRow>sqlite3LogEst((u64)n) ){
          p->nSelectRow = sqlite3LogEst((u64)n);
          p->selFlags |= SF_FixedLimit;
        }
      }else{
        sqlite3ExprCode(pParse, pLimit->pLeft, iLimit);
        sqlite3VdbeAddOp1(v, OP_MustBeInt, iLimit); VdbeCoverage(v);
        VdbeComment((v, "LIMIT counter"));
        sqlite3VdbeAddOp2(v, OP_IfNot, iLimit, iBreak); VdbeCoverage(v);
      }
      if( pLimit->pRight ){
        p->iOffset = iOffset = ++pParse->nMem;
        pParse->nMem++;   /* Allocate an extra register for limit+offset */
        sqlite3ExprCode(pParse, pLimit->pRight, iOffset);
        sqlite3VdbeAddOp1(v, OP_MustBeInt, iOffset); VdbeCoverage(v);
        VdbeComment((v, "OFFSET counter"));
        sqlite3VdbeAddOp3(v, OP_OffsetLimit, iLimit, iOffset+1, iOffset);
        VdbeComment((v, "LIMIT+OFFSET"));
      }
    }
  }
  
  #ifndef SQLITE_OMIT_COMPOUND_SELECT
  /*
  ** Return the appropriate collating sequence for the iCol-th column of
  ** the result set for the compound-select statement "p".  Return NULL if
  ** the column has no default collating sequence.
  **
  ** The collating sequence for the compound select is taken from the
  ** left-most term of the select that has a collating sequence.
  */
  static CollSeq *multiSelectCollSeq(Parse *pParse, Select *p, int iCol){
    CollSeq *pRet;
    if( p->pPrior ){
      pRet = multiSelectCollSeq(pParse, p->pPrior, iCol);
    }else{
      pRet = 0;
    }
    assert( iCol>=0 );
    /* iCol must be less than p->pEList->nExpr.  Otherwise an error would
    ** have been thrown during name resolution and we would not have gotten
    ** this far */
    if( pRet==0 && ALWAYS(iCol<p->pEList->nExpr) ){
      pRet = sqlite3ExprCollSeq(pParse, p->pEList->a[iCol].pExpr);
    }
    return pRet;
  }
  
  /*
  ** The select statement passed as the second parameter is a compound SELECT
  ** with an ORDER BY clause. This function allocates and returns a KeyInfo
  ** structure suitable for implementing the ORDER BY.
  **
  ** Space to hold the KeyInfo structure is obtained from malloc. The calling
  ** function is responsible for ensuring that this structure is eventually
  ** freed.
  */
  static KeyInfo *multiSelectOrderByKeyInfo(Parse *pParse, Select *p, int nExtra){
    ExprList *pOrderBy = p->pOrderBy;
    int nOrderBy = p->pOrderBy->nExpr;
    sqlite3 *db = pParse->db;
    KeyInfo *pRet = sqlite3KeyInfoAlloc(db, nOrderBy+nExtra, 1);
    if( pRet ){
      int i;
      for(i=0; i<nOrderBy; i++){
        struct ExprList_item *pItem = &pOrderBy->a[i];
        Expr *pTerm = pItem->pExpr;
        CollSeq *pColl;
  
        if( pTerm->flags & EP_Collate ){
          pColl = sqlite3ExprCollSeq(pParse, pTerm);
        }else{
          pColl = multiSelectCollSeq(pParse, p, pItem->u.x.iOrderByCol-1);
          if( pColl==0 ) pColl = db->pDfltColl;
          pOrderBy->a[i].pExpr =
            sqlite3ExprAddCollateString(pParse, pTerm, pColl->zName);
        }
        assert( sqlite3KeyInfoIsWriteable(pRet) );
        pRet->aColl[i] = pColl;
        pRet->aSortFlags[i] = pOrderBy->a[i].sortFlags;
      }
    }
  
    return pRet;
  }
  
  #ifndef SQLITE_OMIT_CTE
  /*
  ** This routine generates VDBE code to compute the content of a WITH RECURSIVE
  ** query of the form:
  **
  **   <recursive-table> AS (<setup-query> UNION [ALL] <recursive-query>)
  **                         \___________/             \_______________/
  **                           p->pPrior                      p
  **
  **
  ** There is exactly one reference to the recursive-table in the FROM clause
  ** of recursive-query, marked with the SrcList->a[].fg.isRecursive flag.
  **
  ** The setup-query runs once to generate an initial set of rows that go
  ** into a Queue table.  Rows are extracted from the Queue table one by
  ** one.  Each row extracted from Queue is output to pDest.  Then the single
  ** extracted row (now in the iCurrent table) becomes the content of the
  ** recursive-table for a recursive-query run.  The output of the recursive-query
  ** is added back into the Queue table.  Then another row is extracted from Queue
  ** and the iteration continues until the Queue table is empty.
  **
  ** If the compound query operator is UNION then no duplicate rows are ever
  ** inserted into the Queue table.  The iDistinct table keeps a copy of all rows
  ** that have ever been inserted into Queue and causes duplicates to be
  ** discarded.  If the operator is UNION ALL, then duplicates are allowed.
  ** 
  ** If the query has an ORDER BY, then entries in the Queue table are kept in
  ** ORDER BY order and the first entry is extracted for each cycle.  Without
  ** an ORDER BY, the Queue table is just a FIFO.
  **
  ** If a LIMIT clause is provided, then the iteration stops after LIMIT rows
  ** have been output to pDest.  A LIMIT of zero means to output no rows and a
  ** negative LIMIT means to output all rows.  If there is also an OFFSET clause
  ** with a positive value, then the first OFFSET outputs are discarded rather
  ** than being sent to pDest.  The LIMIT count does not begin until after OFFSET
  ** rows have been skipped.
  */
  static void generateWithRecursiveQuery(
    Parse *pParse,        /* Parsing context */
    Select *p,            /* The recursive SELECT to be coded */
    SelectDest *pDest     /* What to do with query results */
  ){
    SrcList *pSrc = p->pSrc;      /* The FROM clause of the recursive query */
    int nCol = p->pEList->nExpr;  /* Number of columns in the recursive table */
    Vdbe *v = pParse->pVdbe;      /* The prepared statement under construction */
    Select *pSetup = p->pPrior;   /* The setup query */
    Select *pFirstRec;            /* Left-most recursive term */
    int addrTop;                  /* Top of the loop */
    int addrCont, addrBreak;      /* CONTINUE and BREAK addresses */
    int iCurrent = 0;             /* The Current table */
    int regCurrent;               /* Register holding Current table */
    int iQueue;                   /* The Queue table */
    int iDistinct = 0;            /* To ensure unique results if UNION */
    int eDest = SRT_Fifo;         /* How to write to Queue */
    SelectDest destQueue;         /* SelectDest targetting the Queue table */
    int i;                        /* Loop counter */
    int rc;                       /* Result code */
    ExprList *pOrderBy;           /* The ORDER BY clause */
    Expr *pLimit;                 /* Saved LIMIT and OFFSET */
    int regLimit, regOffset;      /* Registers used by LIMIT and OFFSET */
  
  #ifndef SQLITE_OMIT_WINDOWFUNC
    if( p->pWin ){
      sqlite3ErrorMsg(pParse, "cannot use window functions in recursive queries");
      return;
    }
  #endif
  
    /* Obtain authorization to do a recursive query */
    if( sqlite3AuthCheck(pParse, SQLITE_RECURSIVE, 0, 0, 0) ) return;
  
    /* Process the LIMIT and OFFSET clauses, if they exist */
    addrBreak = sqlite3VdbeMakeLabel(pParse);
    p->nSelectRow = 320;  /* 4 billion rows */
    computeLimitRegisters(pParse, p, addrBreak);
    pLimit = p->pLimit;
    regLimit = p->iLimit;
    regOffset = p->iOffset;
    p->pLimit = 0;
    p->iLimit = p->iOffset = 0;
    pOrderBy = p->pOrderBy;
  
    /* Locate the cursor number of the Current table */
    for(i=0; ALWAYS(i<pSrc->nSrc); i++){
      if( pSrc->a[i].fg.isRecursive ){
        iCurrent = pSrc->a[i].iCursor;
        break;
      }
    }
  
    /* Allocate cursors numbers for Queue and Distinct.  The cursor number for
    ** the Distinct table must be exactly one greater than Queue in order
    ** for the SRT_DistFifo and SRT_DistQueue destinations to work. */
    iQueue = pParse->nTab++;
    if( p->op==TK_UNION ){
      eDest = pOrderBy ? SRT_DistQueue : SRT_DistFifo;
      iDistinct = pParse->nTab++;
    }else{
      eDest = pOrderBy ? SRT_Queue : SRT_Fifo;
    }
    sqlite3SelectDestInit(&destQueue, eDest, iQueue);
  
    /* Allocate cursors for Current, Queue, and Distinct. */
    regCurrent = ++pParse->nMem;
    sqlite3VdbeAddOp3(v, OP_OpenPseudo, iCurrent, regCurrent, nCol);
    if( pOrderBy ){
      KeyInfo *pKeyInfo = multiSelectOrderByKeyInfo(pParse, p, 1);
      sqlite3VdbeAddOp4(v, OP_OpenEphemeral, iQueue, pOrderBy->nExpr+2, 0,
                        (char*)pKeyInfo, P4_KEYINFO);
      destQueue.pOrderBy = pOrderBy;
    }else{
      sqlite3VdbeAddOp2(v, OP_OpenEphemeral, iQueue, nCol);
    }
    VdbeComment((v, "Queue table"));
    if( iDistinct ){
      p->addrOpenEphm[0] = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, iDistinct, 0);
      p->selFlags |= SF_UsesEphemeral;
    }
  
    /* Detach the ORDER BY clause from the compound SELECT */
    p->pOrderBy = 0;
  
    /* Figure out how many elements of the compound SELECT are part of the
    ** recursive query.  Make sure no recursive elements use aggregate
    ** functions.  Mark the recursive elements as UNION ALL even if they
    ** are really UNION because the distinctness will be enforced by the
    ** iDistinct table.  pFirstRec is left pointing to the left-most
    ** recursive term of the CTE.
    */
    pFirstRec = p;
    for(pFirstRec=p; ALWAYS(pFirstRec!=0); pFirstRec=pFirstRec->pPrior){
      if( pFirstRec->selFlags & SF_Aggregate ){
        sqlite3ErrorMsg(pParse, "recursive aggregate queries not supported");
        goto end_of_recursive_query;
      }
      pFirstRec->op = TK_ALL;
      if( (pFirstRec->pPrior->selFlags & SF_Recursive)==0 ) break;
    }
  
    /* Store the results of the setup-query in Queue. */
    pSetup = pFirstRec->pPrior;
    pSetup->pNext = 0;
    ExplainQueryPlan((pParse, 1, "SETUP"));
    rc = sqlite3Select(pParse, pSetup, &destQueue);
    pSetup->pNext = p;
    if( rc ) goto end_of_recursive_query;
  
    /* Find the next row in the Queue and output that row */
    addrTop = sqlite3VdbeAddOp2(v, OP_Rewind, iQueue, addrBreak); VdbeCoverage(v);
  
    /* Transfer the next row in Queue over to Current */
    sqlite3VdbeAddOp1(v, OP_NullRow, iCurrent); /* To reset column cache */
    if( pOrderBy ){
      sqlite3VdbeAddOp3(v, OP_Column, iQueue, pOrderBy->nExpr+1, regCurrent);
    }else{
      sqlite3VdbeAddOp2(v, OP_RowData, iQueue, regCurrent);
    }
    sqlite3VdbeAddOp1(v, OP_Delete, iQueue);
  
    /* Output the single row in Current */
    addrCont = sqlite3VdbeMakeLabel(pParse);
    codeOffset(v, regOffset, addrCont);
    selectInnerLoop(pParse, p, iCurrent,
        0, 0, pDest, addrCont, addrBreak);
    if( regLimit ){
      sqlite3VdbeAddOp2(v, OP_DecrJumpZero, regLimit, addrBreak);
      VdbeCoverage(v);
    }
    sqlite3VdbeResolveLabel(v, addrCont);
  
    /* Execute the recursive SELECT taking the single row in Current as
    ** the value for the recursive-table. Store the results in the Queue.
    */
    pFirstRec->pPrior = 0;
    ExplainQueryPlan((pParse, 1, "RECURSIVE STEP"));
    sqlite3Select(pParse, p, &destQueue);
    assert( pFirstRec->pPrior==0 );
    pFirstRec->pPrior = pSetup;
  
    /* Keep running the loop until the Queue is empty */
    sqlite3VdbeGoto(v, addrTop);
    sqlite3VdbeResolveLabel(v, addrBreak);
  
  end_of_recursive_query:
    sqlite3ExprListDelete(pParse->db, p->pOrderBy);
    p->pOrderBy = pOrderBy;
    p->pLimit = pLimit;
    return;
  }
  #endif /* SQLITE_OMIT_CTE */
  
  /* Forward references */
  static int multiSelectOrderBy(
    Parse *pParse,        /* Parsing context */
    Select *p,            /* The right-most of SELECTs to be coded */
    SelectDest *pDest     /* What to do with query results */
  );
  
  /*
  ** Handle the special case of a compound-select that originates from a
  ** VALUES clause.  By handling this as a special case, we avoid deep
  ** recursion, and thus do not need to enforce the SQLITE_LIMIT_COMPOUND_SELECT
  ** on a VALUES clause.
  **
  ** Because the Select object originates from a VALUES clause:
  **   (1) There is no LIMIT or OFFSET or else there is a LIMIT of exactly 1
  **   (2) All terms are UNION ALL
  **   (3) There is no ORDER BY clause
  **
  ** The "LIMIT of exactly 1" case of condition (1) comes about when a VALUES
  ** clause occurs within scalar expression (ex: "SELECT (VALUES(1),(2),(3))").
  ** The sqlite3CodeSubselect will have added the LIMIT 1 clause in tht case.
  ** Since the limit is exactly 1, we only need to evalutes the left-most VALUES.
  */
  static int multiSelectValues(
    Parse *pParse,        /* Parsing context */
    Select *p,            /* The right-most of SELECTs to be coded */
    SelectDest *pDest     /* What to do with query results */
  ){
    int nRow = 1;
    int rc = 0;
    int bShowAll = p->pLimit==0;
    assert( p->selFlags & SF_MultiValue );
    do{
      assert( p->selFlags & SF_Values );
      assert( p->op==TK_ALL || (p->op==TK_SELECT && p->pPrior==0) );
      assert( p->pNext==0 || p->pEList->nExpr==p->pNext->pEList->nExpr );
  #ifndef SQLITE_OMIT_WINDOWFUNC
      if( p->pWin ) return -1;
  #endif
      if( p->pPrior==0 ) break;
      assert( p->pPrior->pNext==p );
      p = p->pPrior;
      nRow += bShowAll;
    }while(1);
    ExplainQueryPlan((pParse, 0, "SCAN %d CONSTANT ROW%s", nRow,
                      nRow==1 ? "" : "S"));
    while( p ){
      selectInnerLoop(pParse, p, -1, 0, 0, pDest, 1, 1);
      if( !bShowAll ) break;
      p->nSelectRow = nRow;
      p = p->pNext;
    }
    return rc;
  }
  
  /*
  ** Return true if the SELECT statement which is known to be the recursive
  ** part of a recursive CTE still has its anchor terms attached.  If the
  ** anchor terms have already been removed, then return false.
  */
  static int hasAnchor(Select *p){
    while( p && (p->selFlags & SF_Recursive)!=0 ){ p = p->pPrior; }
    return p!=0;
  }
  
  /*
  ** This routine is called to process a compound query form from
  ** two or more separate queries using UNION, UNION ALL, EXCEPT, or
  ** INTERSECT
  **
  ** "p" points to the right-most of the two queries.  the query on the
  ** left is p->pPrior.  The left query could also be a compound query
  ** in which case this routine will be called recursively. 
  **
  ** The results of the total query are to be written into a destination
  ** of type eDest with parameter iParm.
  **
  ** Example 1:  Consider a three-way compound SQL statement.
  **
  **     SELECT a FROM t1 UNION SELECT b FROM t2 UNION SELECT c FROM t3
  **
  ** This statement is parsed up as follows:
  **
  **     SELECT c FROM t3
  **      |
  **      `----->  SELECT b FROM t2
  **                |
  **                `------>  SELECT a FROM t1
  **
  ** The arrows in the diagram above represent the Select.pPrior pointer.
  ** So if this routine is called with p equal to the t3 query, then
  ** pPrior will be the t2 query.  p->op will be TK_UNION in this case.
  **
  ** Notice that because of the way SQLite parses compound SELECTs, the
  ** individual selects always group from left to right.
  */
  static int multiSelect(
    Parse *pParse,        /* Parsing context */
    Select *p,            /* The right-most of SELECTs to be coded */
    SelectDest *pDest     /* What to do with query results */
  ){
    int rc = SQLITE_OK;   /* Success code from a subroutine */
    Select *pPrior;       /* Another SELECT immediately to our left */
    Vdbe *v;              /* Generate code to this VDBE */
    SelectDest dest;      /* Alternative data destination */
    Select *pDelete = 0;  /* Chain of simple selects to delete */
    sqlite3 *db;          /* Database connection */
  
    /* Make sure there is no ORDER BY or LIMIT clause on prior SELECTs.  Only
    ** the last (right-most) SELECT in the series may have an ORDER BY or LIMIT.
    */
    assert( p && p->pPrior );  /* Calling function guarantees this much */
    assert( (p->selFlags & SF_Recursive)==0 || p->op==TK_ALL || p->op==TK_UNION );
    assert( p->selFlags & SF_Compound );
    db = pParse->db;
    pPrior = p->pPrior;
    dest = *pDest;
    assert( pPrior->pOrderBy==0 );
    assert( pPrior->pLimit==0 );
  
    v = sqlite3GetVdbe(pParse);
    assert( v!=0 );  /* The VDBE already created by calling function */
  
    /* Create the destination temporary table if necessary
    */
    if( dest.eDest==SRT_EphemTab ){
      assert( p->pEList );
      sqlite3VdbeAddOp2(v, OP_OpenEphemeral, dest.iSDParm, p->pEList->nExpr);
      dest.eDest = SRT_Table;
    }
  
    /* Special handling for a compound-select that originates as a VALUES clause.
    */
    if( p->selFlags & SF_MultiValue ){
      rc = multiSelectValues(pParse, p, &dest);
      if( rc>=0 ) goto multi_select_end;
      rc = SQLITE_OK;
    }
  
    /* Make sure all SELECTs in the statement have the same number of elements
    ** in their result sets.
    */
    assert( p->pEList && pPrior->pEList );
    assert( p->pEList->nExpr==pPrior->pEList->nExpr );
  
  #ifndef SQLITE_OMIT_CTE
    if( (p->selFlags & SF_Recursive)!=0 && hasAnchor(p) ){
      generateWithRecursiveQuery(pParse, p, &dest);
    }else
  #endif
  
    /* Compound SELECTs that have an ORDER BY clause are handled separately.
    */
    if( p->pOrderBy ){
      return multiSelectOrderBy(pParse, p, pDest);
    }else{
  
  #ifndef SQLITE_OMIT_EXPLAIN
      if( pPrior->pPrior==0 ){
        ExplainQueryPlan((pParse, 1, "COMPOUND QUERY"));
        ExplainQueryPlan((pParse, 1, "LEFT-MOST SUBQUERY"));
      }
  #endif
  
      /* Generate code for the left and right SELECT statements.
      */
      switch( p->op ){
        case TK_ALL: {
          int addr = 0;
          int nLimit = 0;  /* Initialize to suppress harmless compiler warning */
          assert( !pPrior->pLimit );
          pPrior->iLimit = p->iLimit;
          pPrior->iOffset = p->iOffset;
          pPrior->pLimit = p->pLimit;
          SELECTTRACE(1, pParse, p, ("multiSelect UNION ALL left...\n"));
          rc = sqlite3Select(pParse, pPrior, &dest);
          pPrior->pLimit = 0;
          if( rc ){
            goto multi_select_end;
          }
          p->pPrior = 0;
          p->iLimit = pPrior->iLimit;
          p->iOffset = pPrior->iOffset;
          if( p->iLimit ){
            addr = sqlite3VdbeAddOp1(v, OP_IfNot, p->iLimit); VdbeCoverage(v);
            VdbeComment((v, "Jump ahead if LIMIT reached"));
            if( p->iOffset ){
              sqlite3VdbeAddOp3(v, OP_OffsetLimit,
                                p->iLimit, p->iOffset+1, p->iOffset);
            }
          }
          ExplainQueryPlan((pParse, 1, "UNION ALL"));
          SELECTTRACE(1, pParse, p, ("multiSelect UNION ALL right...\n"));
          rc = sqlite3Select(pParse, p, &dest);
          testcase( rc!=SQLITE_OK );
          pDelete = p->pPrior;
          p->pPrior = pPrior;
          p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
          if( p->pLimit
           && sqlite3ExprIsInteger(p->pLimit->pLeft, &nLimit)
           && nLimit>0 && p->nSelectRow > sqlite3LogEst((u64)nLimit) 
          ){
            p->nSelectRow = sqlite3LogEst((u64)nLimit);
          }
          if( addr ){
            sqlite3VdbeJumpHere(v, addr);
          }
          break;
        }
        case TK_EXCEPT:
        case TK_UNION: {
          int unionTab;    /* Cursor number of the temp table holding result */
          u8 op = 0;       /* One of the SRT_ operations to apply to self */
          int priorOp;     /* The SRT_ operation to apply to prior selects */
          Expr *pLimit;    /* Saved values of p->nLimit  */
          int addr;
          SelectDest uniondest;
    
          testcase( p->op==TK_EXCEPT );
          testcase( p->op==TK_UNION );
          priorOp = SRT_Union;
          if( dest.eDest==priorOp ){
            /* We can reuse a temporary table generated by a SELECT to our
            ** right.
            */
            assert( p->pLimit==0 );      /* Not allowed on leftward elements */
            unionTab = dest.iSDParm;
          }else{
            /* We will need to create our own temporary table to hold the
            ** intermediate results.
            */
            unionTab = pParse->nTab++;
            assert( p->pOrderBy==0 );
            addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, unionTab, 0);
            assert( p->addrOpenEphm[0] == -1 );
            p->addrOpenEphm[0] = addr;
            findRightmost(p)->selFlags |= SF_UsesEphemeral;
            assert( p->pEList );
          }
            
    
          /* Code the SELECT statements to our left
          */
          assert( !pPrior->pOrderBy );
          sqlite3SelectDestInit(&uniondest, priorOp, unionTab);
          SELECTTRACE(1, pParse, p, ("multiSelect EXCEPT/UNION left...\n"));
          rc = sqlite3Select(pParse, pPrior, &uniondest);
          if( rc ){
            goto multi_select_end;
          }
    
          /* Code the current SELECT statement
          */
          if( p->op==TK_EXCEPT ){
            op = SRT_Except;
          }else{
            assert( p->op==TK_UNION );
            op = SRT_Union;
          }
          p->pPrior = 0;
          pLimit = p->pLimit;
          p->pLimit = 0;
          uniondest.eDest = op;
          ExplainQueryPlan((pParse, 1, "%s USING TEMP B-TREE",
                            sqlite3SelectOpName(p->op)));
          SELECTTRACE(1, pParse, p, ("multiSelect EXCEPT/UNION right...\n"));
          rc = sqlite3Select(pParse, p, &uniondest);
          testcase( rc!=SQLITE_OK );
          assert( p->pOrderBy==0 );
          pDelete = p->pPrior;
          p->pPrior = pPrior;
          p->pOrderBy = 0;
          if( p->op==TK_UNION ){
            p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
          }
          sqlite3ExprDelete(db, p->pLimit);
          p->pLimit = pLimit;
          p->iLimit = 0;
          p->iOffset = 0;
    
          /* Convert the data in the temporary table into whatever form
          ** it is that we currently need.
          */
          assert( unionTab==dest.iSDParm || dest.eDest!=priorOp );
          assert( p->pEList || db->mallocFailed );
          if( dest.eDest!=priorOp && db->mallocFailed==0 ){
            int iCont, iBreak, iStart;
            iBreak = sqlite3VdbeMakeLabel(pParse);
            iCont = sqlite3VdbeMakeLabel(pParse);
            computeLimitRegisters(pParse, p, iBreak);
            sqlite3VdbeAddOp2(v, OP_Rewind, unionTab, iBreak); VdbeCoverage(v);
            iStart = sqlite3VdbeCurrentAddr(v);
            selectInnerLoop(pParse, p, unionTab,
                            0, 0, &dest, iCont, iBreak);
            sqlite3VdbeResolveLabel(v, iCont);
            sqlite3VdbeAddOp2(v, OP_Next, unionTab, iStart); VdbeCoverage(v);
            sqlite3VdbeResolveLabel(v, iBreak);
            sqlite3VdbeAddOp2(v, OP_Close, unionTab, 0);
          }
          break;
        }
        default: assert( p->op==TK_INTERSECT ); {
          int tab1, tab2;
          int iCont, iBreak, iStart;
          Expr *pLimit;
          int addr;
          SelectDest intersectdest;
          int r1;
    
          /* INTERSECT is different from the others since it requires
          ** two temporary tables.  Hence it has its own case.  Begin
          ** by allocating the tables we will need.
          */
          tab1 = pParse->nTab++;
          tab2 = pParse->nTab++;
          assert( p->pOrderBy==0 );
    
          addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, tab1, 0);
          assert( p->addrOpenEphm[0] == -1 );
          p->addrOpenEphm[0] = addr;
          findRightmost(p)->selFlags |= SF_UsesEphemeral;
          assert( p->pEList );
    
          /* Code the SELECTs to our left into temporary table "tab1".
          */
          sqlite3SelectDestInit(&intersectdest, SRT_Union, tab1);
          SELECTTRACE(1, pParse, p, ("multiSelect INTERSECT left...\n"));
          rc = sqlite3Select(pParse, pPrior, &intersectdest);
          if( rc ){
            goto multi_select_end;
          }
    
          /* Code the current SELECT into temporary table "tab2"
          */
          addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, tab2, 0);
          assert( p->addrOpenEphm[1] == -1 );
          p->addrOpenEphm[1] = addr;
          p->pPrior = 0;
          pLimit = p->pLimit;
          p->pLimit = 0;
          intersectdest.iSDParm = tab2;
          ExplainQueryPlan((pParse, 1, "%s USING TEMP B-TREE",
                            sqlite3SelectOpName(p->op)));
          SELECTTRACE(1, pParse, p, ("multiSelect INTERSECT right...\n"));
          rc = sqlite3Select(pParse, p, &intersectdest);
          testcase( rc!=SQLITE_OK );
          pDelete = p->pPrior;
          p->pPrior = pPrior;
          if( p->nSelectRow>pPrior->nSelectRow ){
            p->nSelectRow = pPrior->nSelectRow;
          }
          sqlite3ExprDelete(db, p->pLimit);
          p->pLimit = pLimit;
    
          /* Generate code to take the intersection of the two temporary
          ** tables.
          */
          if( rc ) break;
          assert( p->pEList );
          iBreak = sqlite3VdbeMakeLabel(pParse);
          iCont = sqlite3VdbeMakeLabel(pParse);
          computeLimitRegisters(pParse, p, iBreak);
          sqlite3VdbeAddOp2(v, OP_Rewind, tab1, iBreak); VdbeCoverage(v);
          r1 = sqlite3GetTempReg(pParse);
          iStart = sqlite3VdbeAddOp2(v, OP_RowData, tab1, r1);
          sqlite3VdbeAddOp4Int(v, OP_NotFound, tab2, iCont, r1, 0);
          VdbeCoverage(v);
          sqlite3ReleaseTempReg(pParse, r1);
          selectInnerLoop(pParse, p, tab1,
                          0, 0, &dest, iCont, iBreak);
          sqlite3VdbeResolveLabel(v, iCont);
          sqlite3VdbeAddOp2(v, OP_Next, tab1, iStart); VdbeCoverage(v);
          sqlite3VdbeResolveLabel(v, iBreak);
          sqlite3VdbeAddOp2(v, OP_Close, tab2, 0);
          sqlite3VdbeAddOp2(v, OP_Close, tab1, 0);
          break;
        }
      }
    
    #ifndef SQLITE_OMIT_EXPLAIN
      if( p->pNext==0 ){
        ExplainQueryPlanPop(pParse);
      }
    #endif
    }
    if( pParse->nErr ) goto multi_select_end;
    
    /* Compute collating sequences used by 
    ** temporary tables needed to implement the compound select.
    ** Attach the KeyInfo structure to all temporary tables.
    **
    ** This section is run by the right-most SELECT statement only.
    ** SELECT statements to the left always skip this part.  The right-most
    ** SELECT might also skip this part if it has no ORDER BY clause and
    ** no temp tables are required.
    */
    if( p->selFlags & SF_UsesEphemeral ){
      int i;                        /* Loop counter */
      KeyInfo *pKeyInfo;            /* Collating sequence for the result set */
      Select *pLoop;                /* For looping through SELECT statements */
      CollSeq **apColl;             /* For looping through pKeyInfo->aColl[] */
      int nCol;                     /* Number of columns in result set */
  
      assert( p->pNext==0 );
      nCol = p->pEList->nExpr;
      pKeyInfo = sqlite3KeyInfoAlloc(db, nCol, 1);
      if( !pKeyInfo ){
        rc = SQLITE_NOMEM_BKPT;
        goto multi_select_end;
      }
      for(i=0, apColl=pKeyInfo->aColl; i<nCol; i++, apColl++){
        *apColl = multiSelectCollSeq(pParse, p, i);
        if( 0==*apColl ){
          *apColl = db->pDfltColl;
        }
      }
  
      for(pLoop=p; pLoop; pLoop=pLoop->pPrior){
        for(i=0; i<2; i++){
          int addr = pLoop->addrOpenEphm[i];
          if( addr<0 ){
            /* If [0] is unused then [1] is also unused.  So we can
            ** always safely abort as soon as the first unused slot is found */
            assert( pLoop->addrOpenEphm[1]<0 );
            break;
          }
          sqlite3VdbeChangeP2(v, addr, nCol);
          sqlite3VdbeChangeP4(v, addr, (char*)sqlite3KeyInfoRef(pKeyInfo),
                              P4_KEYINFO);
          pLoop->addrOpenEphm[i] = -1;
        }
      }
      sqlite3KeyInfoUnref(pKeyInfo);
    }
  
  multi_select_end:
    pDest->iSdst = dest.iSdst;
    pDest->nSdst = dest.nSdst;
    sqlite3SelectDelete(db, pDelete);
    return rc;
  }
  #endif /* SQLITE_OMIT_COMPOUND_SELECT */
  
  /*
  ** Error message for when two or more terms of a compound select have different
  ** size result sets.
  */
  void sqlite3SelectWrongNumTermsError(Parse *pParse, Select *p){
    if( p->selFlags & SF_Values ){
      sqlite3ErrorMsg(pParse, "all VALUES must have the same number of terms");
    }else{
      sqlite3ErrorMsg(pParse, "SELECTs to the left and right of %s"
        " do not have the same number of result columns",
        sqlite3SelectOpName(p->op));
    }
  }
  
  /*
  ** Code an output subroutine for a coroutine implementation of a
  ** SELECT statment.
  **
  ** The data to be output is contained in pIn->iSdst.  There are
  ** pIn->nSdst columns to be output.  pDest is where the output should
  ** be sent.
  **
  ** regReturn is the number of the register holding the subroutine
  ** return address.
  **
  ** If regPrev>0 then it is the first register in a vector that
  ** records the previous output.  mem[regPrev] is a flag that is false
  ** if there has been no previous output.  If regPrev>0 then code is
  ** generated to suppress duplicates.  pKeyInfo is used for comparing
  ** keys.
  **
  ** If the LIMIT found in p->iLimit is reached, jump immediately to
  ** iBreak.
  */
  static int generateOutputSubroutine(
    Parse *pParse,          /* Parsing context */
    Select *p,              /* The SELECT statement */
    SelectDest *pIn,        /* Coroutine supplying data */
    SelectDest *pDest,      /* Where to send the data */
    int regReturn,          /* The return address register */
    int regPrev,            /* Previous result register.  No uniqueness if 0 */
    KeyInfo *pKeyInfo,      /* For comparing with previous entry */
    int iBreak              /* Jump here if we hit the LIMIT */
  ){
    Vdbe *v = pParse->pVdbe;
    int iContinue;
    int addr;
  
    addr = sqlite3VdbeCurrentAddr(v);
    iContinue = sqlite3VdbeMakeLabel(pParse);
  
    /* Suppress duplicates for UNION, EXCEPT, and INTERSECT 
    */
    if( regPrev ){
      int addr1, addr2;
      addr1 = sqlite3VdbeAddOp1(v, OP_IfNot, regPrev); VdbeCoverage(v);
      addr2 = sqlite3VdbeAddOp4(v, OP_Compare, pIn->iSdst, regPrev+1, pIn->nSdst,
                                (char*)sqlite3KeyInfoRef(pKeyInfo), P4_KEYINFO);
      sqlite3VdbeAddOp3(v, OP_Jump, addr2+2, iContinue, addr2+2); VdbeCoverage(v);
      sqlite3VdbeJumpHere(v, addr1);
      sqlite3VdbeAddOp3(v, OP_Copy, pIn->iSdst, regPrev+1, pIn->nSdst-1);
      sqlite3VdbeAddOp2(v, OP_Integer, 1, regPrev);
    }
    if( pParse->db->mallocFailed ) return 0;
  
    /* Suppress the first OFFSET entries if there is an OFFSET clause
    */
    codeOffset(v, p->iOffset, iContinue);
  
    assert( pDest->eDest!=SRT_Exists );
    assert( pDest->eDest!=SRT_Table );
    switch( pDest->eDest ){
      /* Store the result as data using a unique key.
      */
      case SRT_EphemTab: {
        int r1 = sqlite3GetTempReg(pParse);
        int r2 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp3(v, OP_MakeRecord, pIn->iSdst, pIn->nSdst, r1);
        sqlite3VdbeAddOp2(v, OP_NewRowid, pDest->iSDParm, r2);
        sqlite3VdbeAddOp3(v, OP_Insert, pDest->iSDParm, r1, r2);
        sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
        sqlite3ReleaseTempReg(pParse, r2);
        sqlite3ReleaseTempReg(pParse, r1);
        break;
      }
  
  #ifndef SQLITE_OMIT_SUBQUERY
      /* If we are creating a set for an "expr IN (SELECT ...)".
      */
      case SRT_Set: {
        int r1;
        testcase( pIn->nSdst>1 );
        r1 = sqlite3GetTempReg(pParse);
        sqlite3VdbeAddOp4(v, OP_MakeRecord, pIn->iSdst, pIn->nSdst, 
            r1, pDest->zAffSdst, pIn->nSdst);
        sqlite3VdbeAddOp4Int(v, OP_IdxInsert, pDest->iSDParm, r1,
                             pIn->iSdst, pIn->nSdst);
        sqlite3ReleaseTempReg(pParse, r1);
        break;
      }
  
      /* If this is a scalar select that is part of an expression, then
      ** store the results in the appropriate memory cell and break out
      ** of the scan loop.  Note that the select might return multiple columns
      ** if it is the RHS of a row-value IN operator.
      */
      case SRT_Mem: {
        testcase( pIn->nSdst>1 );
        sqlite3ExprCodeMove(pParse, pIn->iSdst, pDest->iSDParm, pIn->nSdst);
        /* The LIMIT clause will jump out of the loop for us */
        break;
      }
  #endif /* #ifndef SQLITE_OMIT_SUBQUERY */
  
      /* The results are stored in a sequence of registers
      ** starting at pDest->iSdst.  Then the co-routine yields.
      */
      case SRT_Coroutine: {
        if( pDest->iSdst==0 ){
          pDest->iSdst = sqlite3GetTempRange(pParse, pIn->nSdst);
          pDest->nSdst = pIn->nSdst;
        }
        sqlite3ExprCodeMove(pParse, pIn->iSdst, pDest->iSdst, pIn->nSdst);
        sqlite3VdbeAddOp1(v, OP_Yield, pDest->iSDParm);
        break;
      }
  
      /* If none of the above, then the result destination must be
      ** SRT_Output.  This routine is never called with any other
      ** destination other than the ones handled above or SRT_Output.
      **
      ** For SRT_Output, results are stored in a sequence of registers.  
      ** Then the OP_ResultRow opcode is used to cause sqlite3_step() to
      ** return the next row of result.
      */
      default: {
        assert( pDest->eDest==SRT_Output );
        sqlite3VdbeAddOp2(v, OP_ResultRow, pIn->iSdst, pIn->nSdst);
        break;
      }
    }
  
    /* Jump to the end of the loop if the LIMIT is reached.
    */
    if( p->iLimit ){
      sqlite3VdbeAddOp2(v, OP_DecrJumpZero, p->iLimit, iBreak); VdbeCoverage(v);
    }
  
    /* Generate the subroutine return
    */
    sqlite3VdbeResolveLabel(v, iContinue);
    sqlite3VdbeAddOp1(v, OP_Return, regReturn);
  
    return addr;
  }
  
  /*
  ** Alternative compound select code generator for cases when there
  ** is an ORDER BY clause.
  **
  ** We assume a query of the following form:
  **
  **      <selectA>  <operator>  <selectB>  ORDER BY <orderbylist>
  **
  ** <operator> is one of UNION ALL, UNION, EXCEPT, or INTERSECT.  The idea
  ** is to code both <selectA> and <selectB> with the ORDER BY clause as
  ** co-routines.  Then run the co-routines in parallel and merge the results
  ** into the output.  In addition to the two coroutines (called selectA and
  ** selectB) there are 7 subroutines:
  **
  **    outA:    Move the output of the selectA coroutine into the output
  **             of the compound query.
  **
  **    outB:    Move the output of the selectB coroutine into the output
  **             of the compound query.  (Only generated for UNION and
  **             UNION ALL.  EXCEPT and INSERTSECT never output a row that
  **             appears only in B.)
  **
  **    AltB:    Called when there is data from both coroutines and A<B.
  **
  **    AeqB:    Called when there is data from both coroutines and A==B.
  **
  **    AgtB:    Called when there is data from both coroutines and A>B.
  **
  **    EofA:    Called when data is exhausted from selectA.
  **
  **    EofB:    Called when data is exhausted from selectB.
  **
  ** The implementation of the latter five subroutines depend on which 
  ** <operator> is used:
  **
  **
  **             UNION ALL         UNION            EXCEPT          INTERSECT
  **          -------------  -----------------  --------------  -----------------
  **   AltB:   outA, nextA      outA, nextA       outA, nextA         nextA
  **
  **   AeqB:   outA, nextA         nextA             nextA         outA, nextA
  **
  **   AgtB:   outB, nextB      outB, nextB          nextB            nextB
  **
  **   EofA:   outB, nextB      outB, nextB          halt             halt
  **
  **   EofB:   outA, nextA      outA, nextA       outA, nextA         halt
  **
  ** In the AltB, AeqB, and AgtB subroutines, an EOF on A following nextA
  ** causes an immediate jump to EofA and an EOF on B following nextB causes
  ** an immediate jump to EofB.  Within EofA and EofB, and EOF on entry or
  ** following nextX causes a jump to the end of the select processing.
  **
  ** Duplicate removal in the UNION, EXCEPT, and INTERSECT cases is handled
  ** within the output subroutine.  The regPrev register set holds the previously
  ** output value.  A comparison is made against this value and the output
  ** is skipped if the next results would be the same as the previous.
  **
  ** The implementation plan is to implement the two coroutines and seven
  ** subroutines first, then put the control logic at the bottom.  Like this:
  **
  **          goto Init
  **     coA: coroutine for left query (A)
  **     coB: coroutine for right query (B)
  **    outA: output one row of A
  **    outB: output one row of B (UNION and UNION ALL only)
  **    EofA: ...
  **    EofB: ...
  **    AltB: ...
  **    AeqB: ...
  **    AgtB: ...
  **    Init: initialize coroutine registers
  **          yield coA
  **          if eof(A) goto EofA
  **          yield coB
  **          if eof(B) goto EofB
  **    Cmpr: Compare A, B
  **          Jump AltB, AeqB, AgtB
  **     End: ...
  **
  ** We call AltB, AeqB, AgtB, EofA, and EofB "subroutines" but they are not
  ** actually called using Gosub and they do not Return.  EofA and EofB loop
  ** until all data is exhausted then jump to the "end" labe.  AltB, AeqB,
  ** and AgtB jump to either L2 or to one of EofA or EofB.
  */
  #ifndef SQLITE_OMIT_COMPOUND_SELECT
  static int multiSelectOrderBy(
    Parse *pParse,        /* Parsing context */
    Select *p,            /* The right-most of SELECTs to be coded */
    SelectDest *pDest     /* What to do with query results */
  ){
    int i, j;             /* Loop counters */
    Select *pPrior;       /* Another SELECT immediately to our left */
    Vdbe *v;              /* Generate code to this VDBE */
    SelectDest destA;     /* Destination for coroutine A */
    SelectDest destB;     /* Destination for coroutine B */
    int regAddrA;         /* Address register for select-A coroutine */
    int regAddrB;         /* Address register for select-B coroutine */
    int addrSelectA;      /* Address of the select-A coroutine */
    int addrSelectB;      /* Address of the select-B coroutine */
    int regOutA;          /* Address register for the output-A subroutine */
    int regOutB;          /* Address register for the output-B subroutine */
    int addrOutA;         /* Address of the output-A subroutine */
    int addrOutB = 0;     /* Address of the output-B subroutine */
    int addrEofA;         /* Address of the select-A-exhausted subroutine */
    int addrEofA_noB;     /* Alternate addrEofA if B is uninitialized */
    int addrEofB;         /* Address of the select-B-exhausted subroutine */
    int addrAltB;         /* Address of the A<B subroutine */
    int addrAeqB;         /* Address of the A==B subroutine */
    int addrAgtB;         /* Address of the A>B subroutine */
    int regLimitA;        /* Limit register for select-A */
    int regLimitB;        /* Limit register for select-A */
    int regPrev;          /* A range of registers to hold previous output */
    int savedLimit;       /* Saved value of p->iLimit */
    int savedOffset;      /* Saved value of p->iOffset */
    int labelCmpr;        /* Label for the start of the merge algorithm */
    int labelEnd;         /* Label for the end of the overall SELECT stmt */
    int addr1;            /* Jump instructions that get retargetted */
    int op;               /* One of TK_ALL, TK_UNION, TK_EXCEPT, TK_INTERSECT */
    KeyInfo *pKeyDup = 0; /* Comparison information for duplicate removal */
    KeyInfo *pKeyMerge;   /* Comparison information for merging rows */
    sqlite3 *db;          /* Database connection */
    ExprList *pOrderBy;   /* The ORDER BY clause */
    int nOrderBy;         /* Number of terms in the ORDER BY clause */
    u32 *aPermute;        /* Mapping from ORDER BY terms to result set columns */
  
    assert( p->pOrderBy!=0 );
    assert( pKeyDup==0 ); /* "Managed" code needs this.  Ticket #3382. */
    db = pParse->db;
    v = pParse->pVdbe;
    assert( v!=0 );       /* Already thrown the error if VDBE alloc failed */
    labelEnd = sqlite3VdbeMakeLabel(pParse);
    labelCmpr = sqlite3VdbeMakeLabel(pParse);
  
  
    /* Patch up the ORDER BY clause
    */
    op = p->op;  
    pPrior = p->pPrior;
    assert( pPrior->pOrderBy==0 );
    pOrderBy = p->pOrderBy;
    assert( pOrderBy );
    nOrderBy = pOrderBy->nExpr;
  
    /* For operators other than UNION ALL we have to make sure that
    ** the ORDER BY clause covers every term of the result set.  Add
    ** terms to the ORDER BY clause as necessary.
    */
    if( op!=TK_ALL ){
      for(i=1; db->mallocFailed==0 && i<=p->pEList->nExpr; i++){
        struct ExprList_item *pItem;
        for(j=0, pItem=pOrderBy->a; j<nOrderBy; j++, pItem++){
          assert( pItem->u.x.iOrderByCol>0 );
          if( pItem->u.x.iOrderByCol==i ) break;
        }
        if( j==nOrderBy ){
          Expr *pNew = sqlite3Expr(db, TK_INTEGER, 0);
          if( pNew==0 ) return SQLITE_NOMEM_BKPT;
          pNew->flags |= EP_IntValue;
          pNew->u.iValue = i;
          p->pOrderBy = pOrderBy = sqlite3ExprListAppend(pParse, pOrderBy, pNew);
          if( pOrderBy ) pOrderBy->a[nOrderBy++].u.x.iOrderByCol = (u16)i;
        }
      }
    }
  
    /* Compute the comparison permutation and keyinfo that is used with
    ** the permutation used to determine if the next
    ** row of results comes from selectA or selectB.  Also add explicit
    ** collations to the ORDER BY clause terms so that when the subqueries
    ** to the right and the left are evaluated, they use the correct
    ** collation.
    */
    aPermute = sqlite3DbMallocRawNN(db, sizeof(u32)*(nOrderBy + 1));
    if( aPermute ){
      struct ExprList_item *pItem;
      aPermute[0] = nOrderBy;
      for(i=1, pItem=pOrderBy->a; i<=nOrderBy; i++, pItem++){
        assert( pItem->u.x.iOrderByCol>0 );
        assert( pItem->u.x.iOrderByCol<=p->pEList->nExpr );
        aPermute[i] = pItem->u.x.iOrderByCol - 1;
      }
      pKeyMerge = multiSelectOrderByKeyInfo(pParse, p, 1);
    }else{
      pKeyMerge = 0;
    }
  
    /* Reattach the ORDER BY clause to the query.
    */
    p->pOrderBy = pOrderBy;
    pPrior->pOrderBy = sqlite3ExprListDup(pParse->db, pOrderBy, 0);
  
    /* Allocate a range of temporary registers and the KeyInfo needed
    ** for the logic that removes duplicate result rows when the
    ** operator is UNION, EXCEPT, or INTERSECT (but not UNION ALL).
    */
    if( op==TK_ALL ){
      regPrev = 0;
    }else{
      int nExpr = p->pEList->nExpr;
      assert( nOrderBy>=nExpr || db->mallocFailed );
      regPrev = pParse->nMem+1;
      pParse->nMem += nExpr+1;
      sqlite3VdbeAddOp2(v, OP_Integer, 0, regPrev);
      pKeyDup = sqlite3KeyInfoAlloc(db, nExpr, 1);
      if( pKeyDup ){
        assert( sqlite3KeyInfoIsWriteable(pKeyDup) );
        for(i=0; i<nExpr; i++){
          pKeyDup->aColl[i] = multiSelectCollSeq(pParse, p, i);
          pKeyDup->aSortFlags[i] = 0;
        }
      }
    }
   
    /* Separate the left and the right query from one another
    */
    p->pPrior = 0;
    pPrior->pNext = 0;
    sqlite3ResolveOrderGroupBy(pParse, p, p->pOrderBy, "ORDER");
    if( pPrior->pPrior==0 ){
      sqlite3ResolveOrderGroupBy(pParse, pPrior, pPrior->pOrderBy, "ORDER");
    }
  
    /* Compute the limit registers */
    computeLimitRegisters(pParse, p, labelEnd);
    if( p->iLimit && op==TK_ALL ){
      regLimitA = ++pParse->nMem;
      regLimitB = ++pParse->nMem;
      sqlite3VdbeAddOp2(v, OP_Copy, p->iOffset ? p->iOffset+1 : p->iLimit,
                                    regLimitA);
      sqlite3VdbeAddOp2(v, OP_Copy, regLimitA, regLimitB);
    }else{
      regLimitA = regLimitB = 0;
    }
    sqlite3ExprDelete(db, p->pLimit);
    p->pLimit = 0;
  
    regAddrA = ++pParse->nMem;
    regAddrB = ++pParse->nMem;
    regOutA = ++pParse->nMem;
    regOutB = ++pParse->nMem;
    sqlite3SelectDestInit(&destA, SRT_Coroutine, regAddrA);
    sqlite3SelectDestInit(&destB, SRT_Coroutine, regAddrB);
  
    ExplainQueryPlan((pParse, 1, "MERGE (%s)", sqlite3SelectOpName(p->op)));
  
    /* Generate a coroutine to evaluate the SELECT statement to the
    ** left of the compound operator - the "A" select.
    */
    addrSelectA = sqlite3VdbeCurrentAddr(v) + 1;
    addr1 = sqlite3VdbeAddOp3(v, OP_InitCoroutine, regAddrA, 0, addrSelectA);
    VdbeComment((v, "left SELECT"));
    pPrior->iLimit = regLimitA;
    ExplainQueryPlan((pParse, 1, "LEFT"));
    sqlite3Select(pParse, pPrior, &destA);
    sqlite3VdbeEndCoroutine(v, regAddrA);
    sqlite3VdbeJumpHere(v, addr1);
  
    /* Generate a coroutine to evaluate the SELECT statement on 
    ** the right - the "B" select
    */
    addrSelectB = sqlite3VdbeCurrentAddr(v) + 1;
    addr1 = sqlite3VdbeAddOp3(v, OP_InitCoroutine, regAddrB, 0, addrSelectB);
    VdbeComment((v, "right SELECT"));
    savedLimit = p->iLimit;
    savedOffset = p->iOffset;
    p->iLimit = regLimitB;
    p->iOffset = 0;  
    ExplainQueryPlan((pParse, 1, "RIGHT"));
    sqlite3Select(pParse, p, &destB);
    p->iLimit = savedLimit;
    p->iOffset = savedOffset;
    sqlite3VdbeEndCoroutine(v, regAddrB);
  
    /* Generate a subroutine that outputs the current row of the A
    ** select as the next output row of the compound select.
    */
    VdbeNoopComment((v, "Output routine for A"));
    addrOutA = generateOutputSubroutine(pParse,
                   p, &destA, pDest, regOutA,
                   regPrev, pKeyDup, labelEnd);
    
    /* Generate a subroutine that outputs the current row of the B
    ** select as the next output row of the compound select.
    */
    if( op==TK_ALL || op==TK_UNION ){
      VdbeNoopComment((v, "Output routine for B"));
      addrOutB = generateOutputSubroutine(pParse,
                   p, &destB, pDest, regOutB,
                   regPrev, pKeyDup, labelEnd);
    }
    sqlite3KeyInfoUnref(pKeyDup);
  
    /* Generate a subroutine to run when the results from select A
    ** are exhausted and only data in select B remains.
    */
    if( op==TK_EXCEPT || op==TK_INTERSECT ){
      addrEofA_noB = addrEofA = labelEnd;
    }else{  
      VdbeNoopComment((v, "eof-A subroutine"));
      addrEofA = sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
      addrEofA_noB = sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, labelEnd);
                                       VdbeCoverage(v);
      sqlite3VdbeGoto(v, addrEofA);
      p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
    }
  
    /* Generate a subroutine to run when the results from select B
    ** are exhausted and only data in select A remains.
    */
    if( op==TK_INTERSECT ){
      addrEofB = addrEofA;
      if( p->nSelectRow > pPrior->nSelectRow ) p->nSelectRow = pPrior->nSelectRow;
    }else{  
      VdbeNoopComment((v, "eof-B subroutine"));
      addrEofB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
      sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, labelEnd); VdbeCoverage(v);
      sqlite3VdbeGoto(v, addrEofB);
    }
  
    /* Generate code to handle the case of A<B
    */
    VdbeNoopComment((v, "A-lt-B subroutine"));
    addrAltB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);
    sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA); VdbeCoverage(v);
    sqlite3VdbeGoto(v, labelCmpr);
  
    /* Generate code to handle the case of A==B
    */
    if( op==TK_ALL ){
      addrAeqB = addrAltB;
    }else if( op==TK_INTERSECT ){
      addrAeqB = addrAltB;
      addrAltB++;
    }else{
      VdbeNoopComment((v, "A-eq-B subroutine"));
      addrAeqB =
      sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA); VdbeCoverage(v);
      sqlite3VdbeGoto(v, labelCmpr);
    }
  
    /* Generate code to handle the case of A>B
    */
    VdbeNoopComment((v, "A-gt-B subroutine"));
    addrAgtB = sqlite3VdbeCurrentAddr(v);
    if( op==TK_ALL || op==TK_UNION ){
      sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);
    }
    sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB); VdbeCoverage(v);
    sqlite3VdbeGoto(v, labelCmpr);
  
    /* This code runs once to initialize everything.
    */
    sqlite3VdbeJumpHere(v, addr1);
    sqlite3VdbeAddOp2(v, OP_Yield, regAddrA, addrEofA_noB); VdbeCoverage(v);
    sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, addrEofB); VdbeCoverage(v);
  
    /* Implement the main merge loop
    */
    sqlite3VdbeResolveLabel(v, labelCmpr);
    sqlite3VdbeAddOp4(v, OP_Permutation, 0, 0, 0, (char*)aPermute, P4_INTARRAY);
    sqlite3VdbeAddOp4(v, OP_Compare, destA.iSdst, destB.iSdst, nOrderBy,
                           (char*)pKeyMerge, P4_KEYINFO);
    sqlite3VdbeChangeP5(v, OPFLAG_PERMUTE);
    sqlite3VdbeAddOp3(v, OP_Jump, addrAltB, addrAeqB, addrAgtB); VdbeCoverage(v);
  
    /* Jump to the this point in order to terminate the query.
    */
    sqlite3VdbeResolveLabel(v, labelEnd);
  
    /* Reassembly the compound query so that it will be freed correctly
    ** by the calling function */
    if( p->pPrior ){
      sqlite3SelectDelete(db, p->pPrior);
    }
    p->pPrior = pPrior;
    pPrior->pNext = p;
  
    sqlite3ExprListDelete(db, pPrior->pOrderBy);
    pPrior->pOrderBy = 0;
  
    /*** TBD:  Insert subroutine calls to close cursors on incomplete
    **** subqueries ****/
    ExplainQueryPlanPop(pParse);
    return pParse->nErr!=0;
  }
  #endif
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  
  /* An instance of the SubstContext object describes an substitution edit
  ** to be performed on a parse tree.
  **
  ** All references to columns in table iTable are to be replaced by corresponding
  ** expressions in pEList.
  */
  typedef struct SubstContext {
    Parse *pParse;            /* The parsing context */
    int iTable;               /* Replace references to this table */
    int iNewTable;            /* New table number */
    int isLeftJoin;           /* Add TK_IF_NULL_ROW opcodes on each replacement */
    ExprList *pEList;         /* Replacement expressions */
  } SubstContext;
  
  /* Forward Declarations */
  static void substExprList(SubstContext*, ExprList*);
  static void substSelect(SubstContext*, Select*, int);
  
  /*
  ** Scan through the expression pExpr.  Replace every reference to
  ** a column in table number iTable with a copy of the iColumn-th
  ** entry in pEList.  (But leave references to the ROWID column 
  ** unchanged.)
  **
  ** This routine is part of the flattening procedure.  A subquery
  ** whose result set is defined by pEList appears as entry in the
  ** FROM clause of a SELECT such that the VDBE cursor assigned to that
  ** FORM clause entry is iTable.  This routine makes the necessary 
  ** changes to pExpr so that it refers directly to the source table
  ** of the subquery rather the result set of the subquery.
  */
  static Expr *substExpr(
    SubstContext *pSubst,  /* Description of the substitution */
    Expr *pExpr            /* Expr in which substitution occurs */
  ){
    if( pExpr==0 ) return 0;
    if( ExprHasProperty(pExpr, EP_FromJoin)
     && pExpr->iRightJoinTable==pSubst->iTable
    ){
      pExpr->iRightJoinTable = pSubst->iNewTable;
    }
    if( pExpr->op==TK_COLUMN
     && pExpr->iTable==pSubst->iTable
     && !ExprHasProperty(pExpr, EP_FixedCol)
    ){
  #ifdef SQLITE_ALLOW_ROWID_IN_VIEW
      if( pExpr->iColumn<0 ){
        pExpr->op = TK_NULL;
      }else
  #endif
      {
        Expr *pNew;
        Expr *pCopy = pSubst->pEList->a[pExpr->iColumn].pExpr;
        Expr ifNullRow;
        assert( pSubst->pEList!=0 && pExpr->iColumn<pSubst->pEList->nExpr );
        assert( pExpr->pRight==0 );
        if( sqlite3ExprIsVector(pCopy) ){
          sqlite3VectorErrorMsg(pSubst->pParse, pCopy);
        }else{
          sqlite3 *db = pSubst->pParse->db;
          if( pSubst->isLeftJoin && pCopy->op!=TK_COLUMN ){
            memset(&ifNullRow, 0, sizeof(ifNullRow));
            ifNullRow.op = TK_IF_NULL_ROW;
            ifNullRow.pLeft = pCopy;
            ifNullRow.iTable = pSubst->iNewTable;
            ifNullRow.flags = EP_IfNullRow;
            pCopy = &ifNullRow;
          }
          testcase( ExprHasProperty(pCopy, EP_Subquery) );
          pNew = sqlite3ExprDup(db, pCopy, 0);
          if( db->mallocFailed ){
            sqlite3ExprDelete(db, pNew);
            return pExpr;
          }
          if( pSubst->isLeftJoin ){
            ExprSetProperty(pNew, EP_CanBeNull);
          }
          if( ExprHasProperty(pExpr,EP_FromJoin) ){
            sqlite3SetJoinExpr(pNew, pExpr->iRightJoinTable);
          }
          sqlite3ExprDelete(db, pExpr);
          pExpr = pNew;
  
          /* Ensure that the expression now has an implicit collation sequence,
          ** just as it did when it was a column of a view or sub-query. */
          if( pExpr->op!=TK_COLUMN && pExpr->op!=TK_COLLATE ){
            CollSeq *pColl = sqlite3ExprCollSeq(pSubst->pParse, pExpr);
            pExpr = sqlite3ExprAddCollateString(pSubst->pParse, pExpr, 
                (pColl ? pColl->zName : "BINARY")
            );
          }
          ExprClearProperty(pExpr, EP_Collate);
        }
      }
    }else{
      if( pExpr->op==TK_IF_NULL_ROW && pExpr->iTable==pSubst->iTable ){
        pExpr->iTable = pSubst->iNewTable;
      }
      pExpr->pLeft = substExpr(pSubst, pExpr->pLeft);
      pExpr->pRight = substExpr(pSubst, pExpr->pRight);
      if( ExprHasProperty(pExpr, EP_xIsSelect) ){
        substSelect(pSubst, pExpr->x.pSelect, 1);
      }else{
        substExprList(pSubst, pExpr->x.pList);
      }
  #ifndef SQLITE_OMIT_WINDOWFUNC
      if( ExprHasProperty(pExpr, EP_WinFunc) ){
        Window *pWin = pExpr->y.pWin;
        pWin->pFilter = substExpr(pSubst, pWin->pFilter);
        substExprList(pSubst, pWin->pPartition);
        substExprList(pSubst, pWin->pOrderBy);
      }
  #endif
    }
    return pExpr;
  }
  static void substExprList(
    SubstContext *pSubst, /* Description of the substitution */
    ExprList *pList       /* List to scan and in which to make substitutes */
  ){
    int i;
    if( pList==0 ) return;
    for(i=0; i<pList->nExpr; i++){
      pList->a[i].pExpr = substExpr(pSubst, pList->a[i].pExpr);
    }
  }
  static void substSelect(
    SubstContext *pSubst, /* Description of the substitution */
    Select *p,            /* SELECT statement in which to make substitutions */
    int doPrior           /* Do substitutes on p->pPrior too */
  ){
    SrcList *pSrc;
    SrcItem *pItem;
    int i;
    if( !p ) return;
    do{
      substExprList(pSubst, p->pEList);
      substExprList(pSubst, p->pGroupBy);
      substExprList(pSubst, p->pOrderBy);
      p->pHaving = substExpr(pSubst, p->pHaving);
      p->pWhere = substExpr(pSubst, p->pWhere);
      pSrc = p->pSrc;
      assert( pSrc!=0 );
      for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){
        substSelect(pSubst, pItem->pSelect, 1);
        if( pItem->fg.isTabFunc ){
          substExprList(pSubst, pItem->u1.pFuncArg);
        }
      }
    }while( doPrior && (p = p->pPrior)!=0 );
  }
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  /*
  ** pSelect is a SELECT statement and pSrcItem is one item in the FROM
  ** clause of that SELECT.
  **
  ** This routine scans the entire SELECT statement and recomputes the
  ** pSrcItem->colUsed mask.
  */
  static int recomputeColumnsUsedExpr(Walker *pWalker, Expr *pExpr){
    SrcItem *pItem;
    if( pExpr->op!=TK_COLUMN ) return WRC_Continue;
    pItem = pWalker->u.pSrcItem;
    if( pItem->iCursor!=pExpr->iTable ) return WRC_Continue;
    if( pExpr->iColumn<0 ) return WRC_Continue;
    pItem->colUsed |= sqlite3ExprColUsed(pExpr);
    return WRC_Continue;
  }
  static void recomputeColumnsUsed(
    Select *pSelect,                 /* The complete SELECT statement */
    SrcItem *pSrcItem                /* Which FROM clause item to recompute */
  ){
    Walker w;
    if( NEVER(pSrcItem->pTab==0) ) return;
    memset(&w, 0, sizeof(w));
    w.xExprCallback = recomputeColumnsUsedExpr;
    w.xSelectCallback = sqlite3SelectWalkNoop;
    w.u.pSrcItem = pSrcItem;
    pSrcItem->colUsed = 0;
    sqlite3WalkSelect(&w, pSelect);
  }
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  /*
  ** Assign new cursor numbers to each of the items in pSrc. For each
  ** new cursor number assigned, set an entry in the aCsrMap[] array 
  ** to map the old cursor number to the new:
  **
  **     aCsrMap[iOld] = iNew;
  **
  ** The array is guaranteed by the caller to be large enough for all
  ** existing cursor numbers in pSrc.
  **
  ** If pSrc contains any sub-selects, call this routine recursively
  ** on the FROM clause of each such sub-select, with iExcept set to -1.
  */
  static void srclistRenumberCursors(
    Parse *pParse,                  /* Parse context */
    int *aCsrMap,                   /* Array to store cursor mappings in */
    SrcList *pSrc,                  /* FROM clause to renumber */
    int iExcept                     /* FROM clause item to skip */
  ){
    int i;
    SrcItem *pItem;
    for(i=0, pItem=pSrc->a; i<pSrc->nSrc; i++, pItem++){
      if( i!=iExcept ){
        Select *p;
        if( !pItem->fg.isRecursive || aCsrMap[pItem->iCursor]==0 ){
          aCsrMap[pItem->iCursor] = pParse->nTab++;
        }
        pItem->iCursor = aCsrMap[pItem->iCursor];
        for(p=pItem->pSelect; p; p=p->pPrior){
          srclistRenumberCursors(pParse, aCsrMap, p->pSrc, -1);
        }
      }
    }
  }
  
  /*
  ** Expression walker callback used by renumberCursors() to update
  ** Expr objects to match newly assigned cursor numbers.
  */
  static int renumberCursorsCb(Walker *pWalker, Expr *pExpr){
    int *aCsrMap = pWalker->u.aiCol;
    int op = pExpr->op;
    if( (op==TK_COLUMN || op==TK_IF_NULL_ROW) && aCsrMap[pExpr->iTable] ){
      pExpr->iTable = aCsrMap[pExpr->iTable];
    }
    if( ExprHasProperty(pExpr, EP_FromJoin) && aCsrMap[pExpr->iRightJoinTable] ){
      pExpr->iRightJoinTable = aCsrMap[pExpr->iRightJoinTable];
    }
    return WRC_Continue;
  }
  
  /*
  ** Assign a new cursor number to each cursor in the FROM clause (Select.pSrc)
  ** of the SELECT statement passed as the second argument, and to each 
  ** cursor in the FROM clause of any FROM clause sub-selects, recursively.
  ** Except, do not assign a new cursor number to the iExcept'th element in
  ** the FROM clause of (*p). Update all expressions and other references 
  ** to refer to the new cursor numbers.
  **
  ** Argument aCsrMap is an array that may be used for temporary working
  ** space. Two guarantees are made by the caller:
  **
  **   * the array is larger than the largest cursor number used within the
  **     select statement passed as an argument, and
  **
  **   * the array entries for all cursor numbers that do *not* appear in 
  **     FROM clauses of the select statement as described above are 
  **     initialized to zero.
  */
  static void renumberCursors(
    Parse *pParse,                  /* Parse context */
    Select *p,                      /* Select to renumber cursors within */
    int iExcept,                    /* FROM clause item to skip */
    int *aCsrMap                    /* Working space */
  ){
    Walker w;
    srclistRenumberCursors(pParse, aCsrMap, p->pSrc, iExcept);
    memset(&w, 0, sizeof(w));
    w.u.aiCol = aCsrMap;
    w.xExprCallback = renumberCursorsCb;
    w.xSelectCallback = sqlite3SelectWalkNoop;
    sqlite3WalkSelect(&w, p);
  }
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  /*
  ** This routine attempts to flatten subqueries as a performance optimization.
  ** This routine returns 1 if it makes changes and 0 if no flattening occurs.
  **
  ** To understand the concept of flattening, consider the following
  ** query:
  **
  **     SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5
  **
  ** The default way of implementing this query is to execute the
  ** subquery first and store the results in a temporary table, then
  ** run the outer query on that temporary table.  This requires two
  ** passes over the data.  Furthermore, because the temporary table
  ** has no indices, the WHERE clause on the outer query cannot be
  ** optimized.
  **
  ** This routine attempts to rewrite queries such as the above into
  ** a single flat select, like this:
  **
  **     SELECT x+y AS a FROM t1 WHERE z<100 AND a>5
  **
  ** The code generated for this simplification gives the same result
  ** but only has to scan the data once.  And because indices might 
  ** exist on the table t1, a complete scan of the data might be
  ** avoided.
  **
  ** Flattening is subject to the following constraints:
  **
  **  (**)  We no longer attempt to flatten aggregate subqueries. Was:
  **        The subquery and the outer query cannot both be aggregates.
  **
  **  (**)  We no longer attempt to flatten aggregate subqueries. Was:
  **        (2) If the subquery is an aggregate then
  **        (2a) the outer query must not be a join and
  **        (2b) the outer query must not use subqueries
  **             other than the one FROM-clause subquery that is a candidate
  **             for flattening.  (This is due to ticket [2f7170d73bf9abf80]
  **             from 2015-02-09.)
  **
  **   (3)  If the subquery is the right operand of a LEFT JOIN then
  **        (3a) the subquery may not be a join and
  **        (3b) the FROM clause of the subquery may not contain a virtual
  **             table and
  **        (3c) the outer query may not be an aggregate.
  **        (3d) the outer query may not be DISTINCT.
  **
  **   (4)  The subquery can not be DISTINCT.
  **
  **  (**)  At one point restrictions (4) and (5) defined a subset of DISTINCT
  **        sub-queries that were excluded from this optimization. Restriction 
  **        (4) has since been expanded to exclude all DISTINCT subqueries.
  **
  **  (**)  We no longer attempt to flatten aggregate subqueries.  Was:
  **        If the subquery is aggregate, the outer query may not be DISTINCT.
  **
  **   (7)  The subquery must have a FROM clause.  TODO:  For subqueries without
  **        A FROM clause, consider adding a FROM clause with the special
  **        table sqlite_once that consists of a single row containing a
  **        single NULL.
  **
  **   (8)  If the subquery uses LIMIT then the outer query may not be a join.
  **
  **   (9)  If the subquery uses LIMIT then the outer query may not be aggregate.
  **
  **  (**)  Restriction (10) was removed from the code on 2005-02-05 but we
  **        accidently carried the comment forward until 2014-09-15.  Original
  **        constraint: "If the subquery is aggregate then the outer query 
  **        may not use LIMIT."
  **
  **  (11)  The subquery and the outer query may not both have ORDER BY clauses.
  **
  **  (**)  Not implemented.  Subsumed into restriction (3).  Was previously
  **        a separate restriction deriving from ticket #350.
  **
  **  (13)  The subquery and outer query may not both use LIMIT.
  **
  **  (14)  The subquery may not use OFFSET.
  **
  **  (15)  If the outer query is part of a compound select, then the
  **        subquery may not use LIMIT.
  **        (See ticket #2339 and ticket [02a8e81d44]).
  **
  **  (16)  If the outer query is aggregate, then the subquery may not
  **        use ORDER BY.  (Ticket #2942)  This used to not matter
  **        until we introduced the group_concat() function.  
  **
  **  (17)  If the subquery is a compound select, then
  **        (17a) all compound operators must be a UNION ALL, and
  **        (17b) no terms within the subquery compound may be aggregate
  **              or DISTINCT, and
  **        (17c) every term within the subquery compound must have a FROM clause
  **        (17d) the outer query may not be
  **              (17d1) aggregate, or
  **              (17d2) DISTINCT
  **        (17e) the subquery may not contain window functions, and
  **        (17f) the subquery must not be the RHS of a LEFT JOIN.
  **
  **        The parent and sub-query may contain WHERE clauses. Subject to
  **        rules (11), (13) and (14), they may also contain ORDER BY,
  **        LIMIT and OFFSET clauses.  The subquery cannot use any compound
  **        operator other than UNION ALL because all the other compound
  **        operators have an implied DISTINCT which is disallowed by
  **        restriction (4).
  **
  **        Also, each component of the sub-query must return the same number
  **        of result columns. This is actually a requirement for any compound
  **        SELECT statement, but all the code here does is make sure that no
  **        such (illegal) sub-query is flattened. The caller will detect the
  **        syntax error and return a detailed message.
  **
  **  (18)  If the sub-query is a compound select, then all terms of the
  **        ORDER BY clause of the parent must be copies of a term returned
  **        by the parent query.
  **
  **  (19)  If the subquery uses LIMIT then the outer query may not
  **        have a WHERE clause.
  **
  **  (20)  If the sub-query is a compound select, then it must not use
  **        an ORDER BY clause.  Ticket #3773.  We could relax this constraint
  **        somewhat by saying that the terms of the ORDER BY clause must
  **        appear as unmodified result columns in the outer query.  But we
  **        have other optimizations in mind to deal with that case.
  **
  **  (21)  If the subquery uses LIMIT then the outer query may not be
  **        DISTINCT.  (See ticket [752e1646fc]).
  **
  **  (22)  The subquery may not be a recursive CTE.
  **
  **  (23)  If the outer query is a recursive CTE, then the sub-query may not be
  **        a compound query.  This restriction is because transforming the
  **        parent to a compound query confuses the code that handles
  **        recursive queries in multiSelect().
  **
  **  (**)  We no longer attempt to flatten aggregate subqueries.  Was:
  **        The subquery may not be an aggregate that uses the built-in min() or 
  **        or max() functions.  (Without this restriction, a query like:
  **        "SELECT x FROM (SELECT max(y), x FROM t1)" would not necessarily
  **        return the value X for which Y was maximal.)
  **
  **  (25)  If either the subquery or the parent query contains a window
  **        function in the select list or ORDER BY clause, flattening
  **        is not attempted.
  **
  **
  ** In this routine, the "p" parameter is a pointer to the outer query.
  ** The subquery is p->pSrc->a[iFrom].  isAgg is true if the outer query
  ** uses aggregates.
  **
  ** If flattening is not attempted, this routine is a no-op and returns 0.
  ** If flattening is attempted this routine returns 1.
  **
  ** All of the expression analysis must occur on both the outer query and
  ** the subquery before this routine runs.
  */
  static int flattenSubquery(
    Parse *pParse,       /* Parsing context */
    Select *p,           /* The parent or outer SELECT statement */
    int iFrom,           /* Index in p->pSrc->a[] of the inner subquery */
    int isAgg            /* True if outer SELECT uses aggregate functions */
  ){
    const char *zSavedAuthContext = pParse->zAuthContext;
    Select *pParent;    /* Current UNION ALL term of the other query */
    Select *pSub;       /* The inner query or "subquery" */
    Select *pSub1;      /* Pointer to the rightmost select in sub-query */
    SrcList *pSrc;      /* The FROM clause of the outer query */
    SrcList *pSubSrc;   /* The FROM clause of the subquery */
    int iParent;        /* VDBE cursor number of the pSub result set temp table */
    int iNewParent = -1;/* Replacement table for iParent */
    int isLeftJoin = 0; /* True if pSub is the right side of a LEFT JOIN */    
    int i;              /* Loop counter */
    Expr *pWhere;                    /* The WHERE clause */
    SrcItem *pSubitem;               /* The subquery */
    sqlite3 *db = pParse->db;
    Walker w;                        /* Walker to persist agginfo data */
    int *aCsrMap = 0;
  
    /* Check to see if flattening is permitted.  Return 0 if not.
    */
    assert( p!=0 );
    assert( p->pPrior==0 );
    if( OptimizationDisabled(db, SQLITE_QueryFlattener) ) return 0;
    pSrc = p->pSrc;
    assert( pSrc && iFrom>=0 && iFrom<pSrc->nSrc );
    pSubitem = &pSrc->a[iFrom];
    iParent = pSubitem->iCursor;
    pSub = pSubitem->pSelect;
    assert( pSub!=0 );
  
  #ifndef SQLITE_OMIT_WINDOWFUNC
    if( p->pWin || pSub->pWin ) return 0;                  /* Restriction (25) */
  #endif
  
    pSubSrc = pSub->pSrc;
    assert( pSubSrc );
    /* Prior to version 3.1.2, when LIMIT and OFFSET had to be simple constants,
    ** not arbitrary expressions, we allowed some combining of LIMIT and OFFSET
    ** because they could be computed at compile-time.  But when LIMIT and OFFSET
    ** became arbitrary expressions, we were forced to add restrictions (13)
    ** and (14). */
    if( pSub->pLimit && p->pLimit ) return 0;              /* Restriction (13) */
    if( pSub->pLimit && pSub->pLimit->pRight ) return 0;   /* Restriction (14) */
    if( (p->selFlags & SF_Compound)!=0 && pSub->pLimit ){
      return 0;                                            /* Restriction (15) */
    }
    if( pSubSrc->nSrc==0 ) return 0;                       /* Restriction (7)  */
    if( pSub->selFlags & SF_Distinct ) return 0;           /* Restriction (4)  */
    if( pSub->pLimit && (pSrc->nSrc>1 || isAgg) ){
       return 0;         /* Restrictions (8)(9) */
    }
    if( p->pOrderBy && pSub->pOrderBy ){
       return 0;                                           /* Restriction (11) */
    }
    if( isAgg && pSub->pOrderBy ) return 0;                /* Restriction (16) */
    if( pSub->pLimit && p->pWhere ) return 0;              /* Restriction (19) */
    if( pSub->pLimit && (p->selFlags & SF_Distinct)!=0 ){
       return 0;         /* Restriction (21) */
    }
    if( pSub->selFlags & (SF_Recursive) ){
      return 0; /* Restrictions (22) */
    }
  
    /*
    ** If the subquery is the right operand of a LEFT JOIN, then the
    ** subquery may not be a join itself (3a). Example of why this is not
    ** allowed:
    **
    **         t1 LEFT OUTER JOIN (t2 JOIN t3)
    **
    ** If we flatten the above, we would get
    **
    **         (t1 LEFT OUTER JOIN t2) JOIN t3
    **
    ** which is not at all the same thing.
    **
    ** If the subquery is the right operand of a LEFT JOIN, then the outer
    ** query cannot be an aggregate. (3c)  This is an artifact of the way
    ** aggregates are processed - there is no mechanism to determine if
    ** the LEFT JOIN table should be all-NULL.
    **
    ** See also tickets #306, #350, and #3300.
    */
    if( (pSubitem->fg.jointype & JT_OUTER)!=0 ){
      isLeftJoin = 1;
      if( pSubSrc->nSrc>1                   /* (3a) */
       || isAgg                             /* (3b) */
       || IsVirtual(pSubSrc->a[0].pTab)     /* (3c) */
       || (p->selFlags & SF_Distinct)!=0    /* (3d) */
      ){
        return 0;
      }
    }
  #ifdef SQLITE_EXTRA_IFNULLROW
    else if( iFrom>0 && !isAgg ){
      /* Setting isLeftJoin to -1 causes OP_IfNullRow opcodes to be generated for
      ** every reference to any result column from subquery in a join, even
      ** though they are not necessary.  This will stress-test the OP_IfNullRow 
      ** opcode. */
      isLeftJoin = -1;
    }
  #endif
  
    /* Restriction (17): If the sub-query is a compound SELECT, then it must
    ** use only the UNION ALL operator. And none of the simple select queries
    ** that make up the compound SELECT are allowed to be aggregate or distinct
    ** queries.
    */
    if( pSub->pPrior ){
      if( pSub->pOrderBy ){
        return 0;  /* Restriction (20) */
      }
      if( isAgg || (p->selFlags & SF_Distinct)!=0 || isLeftJoin>0 ){
        return 0; /* (17d1), (17d2), or (17f) */
      }
      for(pSub1=pSub; pSub1; pSub1=pSub1->pPrior){
        testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct );
        testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Aggregate );
        assert( pSub->pSrc!=0 );
        assert( (pSub->selFlags & SF_Recursive)==0 );
        assert( pSub->pEList->nExpr==pSub1->pEList->nExpr );
        if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0    /* (17b) */
         || (pSub1->pPrior && pSub1->op!=TK_ALL)                 /* (17a) */
         || pSub1->pSrc->nSrc<1                                  /* (17c) */
  #ifndef SQLITE_OMIT_WINDOWFUNC
         || pSub1->pWin                                          /* (17e) */
  #endif
        ){
          return 0;
        }
        testcase( pSub1->pSrc->nSrc>1 );
      }
  
      /* Restriction (18). */
      if( p->pOrderBy ){
        int ii;
        for(ii=0; ii<p->pOrderBy->nExpr; ii++){
          if( p->pOrderBy->a[ii].u.x.iOrderByCol==0 ) return 0;
        }
      }
  
      /* Restriction (23) */
      if( (p->selFlags & SF_Recursive) ) return 0;
  
      if( pSrc->nSrc>1 ){
        if( pParse->nSelect>500 ) return 0;
        aCsrMap = sqlite3DbMallocZero(db, pParse->nTab*sizeof(int));
      }
    }
  
    /***** If we reach this point, flattening is permitted. *****/
    SELECTTRACE(1,pParse,p,("flatten %u.%p from term %d\n",
                     pSub->selId, pSub, iFrom));
  
    /* Authorize the subquery */
    pParse->zAuthContext = pSubitem->zName;
    TESTONLY(i =) sqlite3AuthCheck(pParse, SQLITE_SELECT, 0, 0, 0);
    testcase( i==SQLITE_DENY );
    pParse->zAuthContext = zSavedAuthContext;
  
    /* Delete the transient structures associated with thesubquery */
    pSub1 = pSubitem->pSelect;
    sqlite3DbFree(db, pSubitem->zDatabase);
    sqlite3DbFree(db, pSubitem->zName);
    sqlite3DbFree(db, pSubitem->zAlias);
    pSubitem->zDatabase = 0;
    pSubitem->zName = 0;
    pSubitem->zAlias = 0;
    pSubitem->pSelect = 0;
    assert( pSubitem->pOn==0 );
  
    /* If the sub-query is a compound SELECT statement, then (by restrictions
    ** 17 and 18 above) it must be a UNION ALL and the parent query must 
    ** be of the form:
    **
    **     SELECT <expr-list> FROM (<sub-query>) <where-clause> 
    **
    ** followed by any ORDER BY, LIMIT and/or OFFSET clauses. This block
    ** creates N-1 copies of the parent query without any ORDER BY, LIMIT or 
    ** OFFSET clauses and joins them to the left-hand-side of the original
    ** using UNION ALL operators. In this case N is the number of simple
    ** select statements in the compound sub-query.
    **
    ** Example:
    **
    **     SELECT a+1 FROM (
    **        SELECT x FROM tab
    **        UNION ALL
    **        SELECT y FROM tab
    **        UNION ALL
    **        SELECT abs(z*2) FROM tab2
    **     ) WHERE a!=5 ORDER BY 1
    **
    ** Transformed into:
    **
    **     SELECT x+1 FROM tab WHERE x+1!=5
    **     UNION ALL
    **     SELECT y+1 FROM tab WHERE y+1!=5
    **     UNION ALL
    **     SELECT abs(z*2)+1 FROM tab2 WHERE abs(z*2)+1!=5
    **     ORDER BY 1
    **
    ** We call this the "compound-subquery flattening".
    */
    for(pSub=pSub->pPrior; pSub; pSub=pSub->pPrior){
      Select *pNew;
      ExprList *pOrderBy = p->pOrderBy;
      Expr *pLimit = p->pLimit;
      Select *pPrior = p->pPrior;
      Table *pItemTab = pSubitem->pTab;
      pSubitem->pTab = 0;
      p->pOrderBy = 0;
      p->pPrior = 0;
      p->pLimit = 0;
      pNew = sqlite3SelectDup(db, p, 0);
      p->pLimit = pLimit;
      p->pOrderBy = pOrderBy;
      p->op = TK_ALL;
      pSubitem->pTab = pItemTab;
      if( pNew==0 ){
        p->pPrior = pPrior;
      }else{
        pNew->selId = ++pParse->nSelect;
        if( aCsrMap && ALWAYS(db->mallocFailed==0) ){
          renumberCursors(pParse, pNew, iFrom, aCsrMap);
        }
        pNew->pPrior = pPrior;
        if( pPrior ) pPrior->pNext = pNew;
        pNew->pNext = p;
        p->pPrior = pNew;
        SELECTTRACE(2,pParse,p,("compound-subquery flattener"
                                " creates %u as peer\n",pNew->selId));
      }
      assert( pSubitem->pSelect==0 );
    }
    sqlite3DbFree(db, aCsrMap);
    if( db->mallocFailed ){
      pSubitem->pSelect = pSub1;
      return 1;
    }
  
    /* Defer deleting the Table object associated with the
    ** subquery until code generation is
    ** complete, since there may still exist Expr.pTab entries that
    ** refer to the subquery even after flattening.  Ticket #3346.
    **
    ** pSubitem->pTab is always non-NULL by test restrictions and tests above.
    */
    if( ALWAYS(pSubitem->pTab!=0) ){
      Table *pTabToDel = pSubitem->pTab;
      if( pTabToDel->nTabRef==1 ){
        Parse *pToplevel = sqlite3ParseToplevel(pParse);
        sqlite3ParserAddCleanup(pToplevel, 
           (void(*)(sqlite3*,void*))sqlite3DeleteTable,
           pTabToDel);
        testcase( pToplevel->earlyCleanup );
      }else{
        pTabToDel->nTabRef--;
      }
      pSubitem->pTab = 0;
    }
  
    /* The following loop runs once for each term in a compound-subquery
    ** flattening (as described above).  If we are doing a different kind
    ** of flattening - a flattening other than a compound-subquery flattening -
    ** then this loop only runs once.
    **
    ** This loop moves all of the FROM elements of the subquery into the
    ** the FROM clause of the outer query.  Before doing this, remember
    ** the cursor number for the original outer query FROM element in
    ** iParent.  The iParent cursor will never be used.  Subsequent code
    ** will scan expressions looking for iParent references and replace
    ** those references with expressions that resolve to the subquery FROM
    ** elements we are now copying in.
    */
    pSub = pSub1;
    for(pParent=p; pParent; pParent=pParent->pPrior, pSub=pSub->pPrior){
      int nSubSrc;
      u8 jointype = 0;
      assert( pSub!=0 );
      pSubSrc = pSub->pSrc;     /* FROM clause of subquery */
      nSubSrc = pSubSrc->nSrc;  /* Number of terms in subquery FROM clause */
      pSrc = pParent->pSrc;     /* FROM clause of the outer query */
  
      if( pParent==p ){
        jointype = pSubitem->fg.jointype;     /* First time through the loop */
      }
      
      /* The subquery uses a single slot of the FROM clause of the outer
      ** query.  If the subquery has more than one element in its FROM clause,
      ** then expand the outer query to make space for it to hold all elements
      ** of the subquery.
      **
      ** Example:
      **
      **    SELECT * FROM tabA, (SELECT * FROM sub1, sub2), tabB;
      **
      ** The outer query has 3 slots in its FROM clause.  One slot of the
      ** outer query (the middle slot) is used by the subquery.  The next
      ** block of code will expand the outer query FROM clause to 4 slots.
      ** The middle slot is expanded to two slots in order to make space
      ** for the two elements in the FROM clause of the subquery.
      */
      if( nSubSrc>1 ){
        pSrc = sqlite3SrcListEnlarge(pParse, pSrc, nSubSrc-1,iFrom+1);
        if( pSrc==0 ) break;
        pParent->pSrc = pSrc;
      }
  
      /* Transfer the FROM clause terms from the subquery into the
      ** outer query.
      */
      for(i=0; i<nSubSrc; i++){
        sqlite3IdListDelete(db, pSrc->a[i+iFrom].pUsing);
        assert( pSrc->a[i+iFrom].fg.isTabFunc==0 );
        pSrc->a[i+iFrom] = pSubSrc->a[i];
        iNewParent = pSubSrc->a[i].iCursor;
        memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i]));
      }
      pSrc->a[iFrom].fg.jointype = jointype;
    
      /* Now begin substituting subquery result set expressions for 
      ** references to the iParent in the outer query.
      ** 
      ** Example:
      **
      **   SELECT a+5, b*10 FROM (SELECT x*3 AS a, y+10 AS b FROM t1) WHERE a>b;
      **   \                     \_____________ subquery __________/          /
      **    \_____________________ outer query ______________________________/
      **
      ** We look at every expression in the outer query and every place we see
      ** "a" we substitute "x*3" and every place we see "b" we substitute "y+10".
      */
      if( pSub->pOrderBy && (pParent->selFlags & SF_NoopOrderBy)==0 ){
        /* At this point, any non-zero iOrderByCol values indicate that the
        ** ORDER BY column expression is identical to the iOrderByCol'th
        ** expression returned by SELECT statement pSub. Since these values
        ** do not necessarily correspond to columns in SELECT statement pParent,
        ** zero them before transfering the ORDER BY clause.
        **
        ** Not doing this may cause an error if a subsequent call to this
        ** function attempts to flatten a compound sub-query into pParent
        ** (the only way this can happen is if the compound sub-query is
        ** currently part of pSub->pSrc). See ticket [d11a6e908f].  */
        ExprList *pOrderBy = pSub->pOrderBy;
        for(i=0; i<pOrderBy->nExpr; i++){
          pOrderBy->a[i].u.x.iOrderByCol = 0;
        }
        assert( pParent->pOrderBy==0 );
        pParent->pOrderBy = pOrderBy;
        pSub->pOrderBy = 0;
      }
      pWhere = pSub->pWhere;
      pSub->pWhere = 0;
      if( isLeftJoin>0 ){
        sqlite3SetJoinExpr(pWhere, iNewParent);
      }
      if( pWhere ){
        if( pParent->pWhere ){
          pParent->pWhere = sqlite3PExpr(pParse, TK_AND, pWhere, pParent->pWhere);
        }else{
          pParent->pWhere = pWhere;
        }
      }
      if( db->mallocFailed==0 ){
        SubstContext x;
        x.pParse = pParse;
        x.iTable = iParent;
        x.iNewTable = iNewParent;
        x.isLeftJoin = isLeftJoin;
        x.pEList = pSub->pEList;
        substSelect(&x, pParent, 0);
      }
    
      /* The flattened query is a compound if either the inner or the
      ** outer query is a compound. */
      pParent->selFlags |= pSub->selFlags & SF_Compound;
      assert( (pSub->selFlags & SF_Distinct)==0 ); /* restriction (17b) */
    
      /*
      ** SELECT ... FROM (SELECT ... LIMIT a OFFSET b) LIMIT x OFFSET y;
      **
      ** One is tempted to try to add a and b to combine the limits.  But this
      ** does not work if either limit is negative.
      */
      if( pSub->pLimit ){
        pParent->pLimit = pSub->pLimit;
        pSub->pLimit = 0;
      }
  
      /* Recompute the SrcList_item.colUsed masks for the flattened
      ** tables. */
      for(i=0; i<nSubSrc; i++){
        recomputeColumnsUsed(pParent, &pSrc->a[i+iFrom]);
      }
    }
  
    /* Finially, delete what is left of the subquery and return
    ** success.
    */
    sqlite3AggInfoPersistWalkerInit(&w, pParse);
    sqlite3WalkSelect(&w,pSub1);
    sqlite3SelectDelete(db, pSub1);
  
  #if SELECTTRACE_ENABLED
    if( sqlite3SelectTrace & 0x100 ){
      SELECTTRACE(0x100,pParse,p,("After flattening:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  
    return 1;
  }
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  /*
  ** A structure to keep track of all of the column values that are fixed to
  ** a known value due to WHERE clause constraints of the form COLUMN=VALUE.
  */
  typedef struct WhereConst WhereConst;
  struct WhereConst {
    Parse *pParse;   /* Parsing context */
    u8 *pOomFault;   /* Pointer to pParse->db->mallocFailed */
    int nConst;      /* Number for COLUMN=CONSTANT terms */
    int nChng;       /* Number of times a constant is propagated */
    int bHasAffBlob; /* At least one column in apExpr[] as affinity BLOB */
    Expr **apExpr;   /* [i*2] is COLUMN and [i*2+1] is VALUE */
  };
  
  /*
  ** Add a new entry to the pConst object.  Except, do not add duplicate
  ** pColumn entires.  Also, do not add if doing so would not be appropriate.
  **
  ** The caller guarantees the pColumn is a column and pValue is a constant.
  ** This routine has to do some additional checks before completing the
  ** insert.
  */
  static void constInsert(
    WhereConst *pConst,  /* The WhereConst into which we are inserting */
    Expr *pColumn,       /* The COLUMN part of the constraint */
    Expr *pValue,        /* The VALUE part of the constraint */
    Expr *pExpr          /* Overall expression: COLUMN=VALUE or VALUE=COLUMN */
  ){
    int i;
    assert( pColumn->op==TK_COLUMN );
    assert( sqlite3ExprIsConstant(pValue) );
  
    if( ExprHasProperty(pColumn, EP_FixedCol) ) return;
    if( sqlite3ExprAffinity(pValue)!=0 ) return;
    if( !sqlite3IsBinary(sqlite3ExprCompareCollSeq(pConst->pParse,pExpr)) ){
      return;
    }
  
    /* 2018-10-25 ticket [cf5ed20f]
    ** Make sure the same pColumn is not inserted more than once */
    for(i=0; i<pConst->nConst; i++){
      const Expr *pE2 = pConst->apExpr[i*2];
      assert( pE2->op==TK_COLUMN );
      if( pE2->iTable==pColumn->iTable
       && pE2->iColumn==pColumn->iColumn
      ){
        return;  /* Already present.  Return without doing anything. */
      }
    }
    if( sqlite3ExprAffinity(pColumn)==SQLITE_AFF_BLOB ){
      pConst->bHasAffBlob = 1;
    }
  
    pConst->nConst++;
    pConst->apExpr = sqlite3DbReallocOrFree(pConst->pParse->db, pConst->apExpr,
                           pConst->nConst*2*sizeof(Expr*));
    if( pConst->apExpr==0 ){
      pConst->nConst = 0;
    }else{
      pConst->apExpr[pConst->nConst*2-2] = pColumn;
      pConst->apExpr[pConst->nConst*2-1] = pValue;
    }
  }
  
  /*
  ** Find all terms of COLUMN=VALUE or VALUE=COLUMN in pExpr where VALUE
  ** is a constant expression and where the term must be true because it
  ** is part of the AND-connected terms of the expression.  For each term
  ** found, add it to the pConst structure.
  */
  static void findConstInWhere(WhereConst *pConst, Expr *pExpr){
    Expr *pRight, *pLeft;
    if( NEVER(pExpr==0) ) return;
    if( ExprHasProperty(pExpr, EP_FromJoin) ) return;
    if( pExpr->op==TK_AND ){
      findConstInWhere(pConst, pExpr->pRight);
      findConstInWhere(pConst, pExpr->pLeft);
      return;
    }
    if( pExpr->op!=TK_EQ ) return;
    pRight = pExpr->pRight;
    pLeft = pExpr->pLeft;
    assert( pRight!=0 );
    assert( pLeft!=0 );
    if( pRight->op==TK_COLUMN && sqlite3ExprIsConstant(pLeft) ){
      constInsert(pConst,pRight,pLeft,pExpr);
    }
    if( pLeft->op==TK_COLUMN && sqlite3ExprIsConstant(pRight) ){
      constInsert(pConst,pLeft,pRight,pExpr);
    }
  }
  
  /*
  ** This is a helper function for Walker callback propagateConstantExprRewrite().
  **
  ** Argument pExpr is a candidate expression to be replaced by a value. If 
  ** pExpr is equivalent to one of the columns named in pWalker->u.pConst, 
  ** then overwrite it with the corresponding value. Except, do not do so
  ** if argument bIgnoreAffBlob is non-zero and the affinity of pExpr
  ** is SQLITE_AFF_BLOB.
  */
  static int propagateConstantExprRewriteOne(
    WhereConst *pConst,
    Expr *pExpr, 
    int bIgnoreAffBlob
  ){
    int i;
    if( pConst->pOomFault[0] ) return WRC_Prune;
    if( pExpr->op!=TK_COLUMN ) return WRC_Continue;
    if( ExprHasProperty(pExpr, EP_FixedCol|EP_FromJoin) ){
      testcase( ExprHasProperty(pExpr, EP_FixedCol) );
      testcase( ExprHasProperty(pExpr, EP_FromJoin) );
      return WRC_Continue;
    }
    for(i=0; i<pConst->nConst; i++){
      Expr *pColumn = pConst->apExpr[i*2];
      if( pColumn==pExpr ) continue;
      if( pColumn->iTable!=pExpr->iTable ) continue;
      if( pColumn->iColumn!=pExpr->iColumn ) continue;
      if( bIgnoreAffBlob && sqlite3ExprAffinity(pColumn)==SQLITE_AFF_BLOB ){
        break;
      }
      /* A match is found.  Add the EP_FixedCol property */
      pConst->nChng++;
      ExprClearProperty(pExpr, EP_Leaf);
      ExprSetProperty(pExpr, EP_FixedCol);
      assert( pExpr->pLeft==0 );
      pExpr->pLeft = sqlite3ExprDup(pConst->pParse->db, pConst->apExpr[i*2+1], 0);
      if( pConst->pParse->db->mallocFailed ) return WRC_Prune;
      break;
    }
    return WRC_Prune;
  }
  
  /*
  ** This is a Walker expression callback. pExpr is a node from the WHERE
  ** clause of a SELECT statement. This function examines pExpr to see if
  ** any substitutions based on the contents of pWalker->u.pConst should
  ** be made to pExpr or its immediate children.
  **
  ** A substitution is made if:
  **
  **   + pExpr is a column with an affinity other than BLOB that matches
  **     one of the columns in pWalker->u.pConst, or
  **
  **   + pExpr is a binary comparison operator (=, <=, >=, <, >) that
  **     uses an affinity other than TEXT and one of its immediate
  **     children is a column that matches one of the columns in 
  **     pWalker->u.pConst.
  */
  static int propagateConstantExprRewrite(Walker *pWalker, Expr *pExpr){
    WhereConst *pConst = pWalker->u.pConst;
    assert( TK_GT==TK_EQ+1 );
    assert( TK_LE==TK_EQ+2 );
    assert( TK_LT==TK_EQ+3 );
    assert( TK_GE==TK_EQ+4 );
    if( pConst->bHasAffBlob ){
      if( (pExpr->op>=TK_EQ && pExpr->op<=TK_GE)
       || pExpr->op==TK_IS
      ){
        propagateConstantExprRewriteOne(pConst, pExpr->pLeft, 0);
        if( pConst->pOomFault[0] ) return WRC_Prune;
        if( sqlite3ExprAffinity(pExpr->pLeft)!=SQLITE_AFF_TEXT ){
          propagateConstantExprRewriteOne(pConst, pExpr->pRight, 0);
        }
      }
    }
    return propagateConstantExprRewriteOne(pConst, pExpr, pConst->bHasAffBlob);
  }
  
  /*
  ** The WHERE-clause constant propagation optimization.
  **
  ** If the WHERE clause contains terms of the form COLUMN=CONSTANT or
  ** CONSTANT=COLUMN that are top-level AND-connected terms that are not
  ** part of a ON clause from a LEFT JOIN, then throughout the query
  ** replace all other occurrences of COLUMN with CONSTANT.
  **
  ** For example, the query:
  **
  **      SELECT * FROM t1, t2, t3 WHERE t1.a=39 AND t2.b=t1.a AND t3.c=t2.b
  **
  ** Is transformed into
  **
  **      SELECT * FROM t1, t2, t3 WHERE t1.a=39 AND t2.b=39 AND t3.c=39
  **
  ** Return true if any transformations where made and false if not.
  **
  ** Implementation note:  Constant propagation is tricky due to affinity
  ** and collating sequence interactions.  Consider this example:
  **
  **    CREATE TABLE t1(a INT,b TEXT);
  **    INSERT INTO t1 VALUES(123,'0123');
  **    SELECT * FROM t1 WHERE a=123 AND b=a;
  **    SELECT * FROM t1 WHERE a=123 AND b=123;
  **
  ** The two SELECT statements above should return different answers.  b=a
  ** is alway true because the comparison uses numeric affinity, but b=123
  ** is false because it uses text affinity and '0123' is not the same as '123'.
  ** To work around this, the expression tree is not actually changed from
  ** "b=a" to "b=123" but rather the "a" in "b=a" is tagged with EP_FixedCol
  ** and the "123" value is hung off of the pLeft pointer.  Code generator
  ** routines know to generate the constant "123" instead of looking up the
  ** column value.  Also, to avoid collation problems, this optimization is
  ** only attempted if the "a=123" term uses the default BINARY collation.
  **
  ** 2021-05-25 forum post 6a06202608: Another troublesome case is...
  **
  **    CREATE TABLE t1(x);
  **    INSERT INTO t1 VALUES(10.0);
  **    SELECT 1 FROM t1 WHERE x=10 AND x LIKE 10;
  **
  ** The query should return no rows, because the t1.x value is '10.0' not '10'
  ** and '10.0' is not LIKE '10'.  But if we are not careful, the first WHERE
  ** term "x=10" will cause the second WHERE term to become "10 LIKE 10",
  ** resulting in a false positive.  To avoid this, constant propagation for
  ** columns with BLOB affinity is only allowed if the constant is used with
  ** operators ==, <=, <, >=, >, or IS in a way that will cause the correct
  ** type conversions to occur.  See logic associated with the bHasAffBlob flag
  ** for details.
  */
  static int propagateConstants(
    Parse *pParse,   /* The parsing context */
    Select *p        /* The query in which to propagate constants */
  ){
    WhereConst x;
    Walker w;
    int nChng = 0;
    x.pParse = pParse;
    x.pOomFault = &pParse->db->mallocFailed;
    do{
      x.nConst = 0;
      x.nChng = 0;
      x.apExpr = 0;
      x.bHasAffBlob = 0;
      findConstInWhere(&x, p->pWhere);
      if( x.nConst ){
        memset(&w, 0, sizeof(w));
        w.pParse = pParse;
        w.xExprCallback = propagateConstantExprRewrite;
        w.xSelectCallback = sqlite3SelectWalkNoop;
        w.xSelectCallback2 = 0;
        w.walkerDepth = 0;
        w.u.pConst = &x;
        sqlite3WalkExpr(&w, p->pWhere);
        sqlite3DbFree(x.pParse->db, x.apExpr);
        nChng += x.nChng;
      }
    }while( x.nChng );  
    return nChng;
  }
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  # if !defined(SQLITE_OMIT_WINDOWFUNC)
  /*
  ** This function is called to determine whether or not it is safe to
  ** push WHERE clause expression pExpr down to FROM clause sub-query
  ** pSubq, which contains at least one window function. Return 1
  ** if it is safe and the expression should be pushed down, or 0 
  ** otherwise.
  **
  ** It is only safe to push the expression down if it consists only 
  ** of constants and copies of expressions that appear in the PARTITION
  ** BY clause of all window function used by the sub-query. It is safe
  ** to filter out entire partitions, but not rows within partitions, as
  ** this may change the results of the window functions.
  **
  ** At the time this function is called it is guaranteed that 
  **
  **   * the sub-query uses only one distinct window frame, and 
  **   * that the window frame has a PARTITION BY clase.
  */
  static int pushDownWindowCheck(Parse *pParse, Select *pSubq, Expr *pExpr){
    assert( pSubq->pWin->pPartition );
    assert( (pSubq->selFlags & SF_MultiPart)==0 );
    assert( pSubq->pPrior==0 );
    return sqlite3ExprIsConstantOrGroupBy(pParse, pExpr, pSubq->pWin->pPartition);
  }
  # endif /* SQLITE_OMIT_WINDOWFUNC */
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
  /*
  ** Make copies of relevant WHERE clause terms of the outer query into
  ** the WHERE clause of subquery.  Example:
  **
  **    SELECT * FROM (SELECT a AS x, c-d AS y FROM t1) WHERE x=5 AND y=10;
  **
  ** Transformed into:
  **
  **    SELECT * FROM (SELECT a AS x, c-d AS y FROM t1 WHERE a=5 AND c-d=10)
  **     WHERE x=5 AND y=10;
  **
  ** The hope is that the terms added to the inner query will make it more
  ** efficient.
  **
  ** Do not attempt this optimization if:
  **
  **   (1) (** This restriction was removed on 2017-09-29.  We used to
  **           disallow this optimization for aggregate subqueries, but now
  **           it is allowed by putting the extra terms on the HAVING clause.
  **           The added HAVING clause is pointless if the subquery lacks
  **           a GROUP BY clause.  But such a HAVING clause is also harmless
  **           so there does not appear to be any reason to add extra logic
  **           to suppress it. **)
  **
  **   (2) The inner query is the recursive part of a common table expression.
  **
  **   (3) The inner query has a LIMIT clause (since the changes to the WHERE
  **       clause would change the meaning of the LIMIT).
  **
  **   (4) The inner query is the right operand of a LEFT JOIN and the
  **       expression to be pushed down does not come from the ON clause
  **       on that LEFT JOIN.
  **
  **   (5) The WHERE clause expression originates in the ON or USING clause
  **       of a LEFT JOIN where iCursor is not the right-hand table of that
  **       left join.  An example:
  **
  **           SELECT *
  **           FROM (SELECT 1 AS a1 UNION ALL SELECT 2) AS aa
  **           JOIN (SELECT 1 AS b2 UNION ALL SELECT 2) AS bb ON (a1=b2)
  **           LEFT JOIN (SELECT 8 AS c3 UNION ALL SELECT 9) AS cc ON (b2=2);
  **
  **       The correct answer is three rows:  (1,1,NULL),(2,2,8),(2,2,9).
  **       But if the (b2=2) term were to be pushed down into the bb subquery,
  **       then the (1,1,NULL) row would be suppressed.
  **
  **   (6) Window functions make things tricky as changes to the WHERE clause 
  **       of the inner query could change the window over which window 
  **       functions are calculated. Therefore, do not attempt the optimization
  **       if:
  **
  **     (6a) The inner query uses multiple incompatible window partitions.
  **
  **     (6b) The inner query is a compound and uses window-functions. 
  **
  **     (6c) The WHERE clause does not consist entirely of constants and
  **          copies of expressions found in the PARTITION BY clause of
  **          all window-functions used by the sub-query. It is safe to
  **          filter out entire partitions, as this does not change the 
  **          window over which any window-function is calculated.
  **
  **   (7) The inner query is a Common Table Expression (CTE) that should
  **       be materialized.  (This restriction is implemented in the calling
  **       routine.)
  **
  ** Return 0 if no changes are made and non-zero if one or more WHERE clause
  ** terms are duplicated into the subquery.
  */
  static int pushDownWhereTerms(
    Parse *pParse,        /* Parse context (for malloc() and error reporting) */
    Select *pSubq,        /* The subquery whose WHERE clause is to be augmented */
    Expr *pWhere,         /* The WHERE clause of the outer query */
    int iCursor,          /* Cursor number of the subquery */
    int isLeftJoin        /* True if pSubq is the right term of a LEFT JOIN */
  ){
    Expr *pNew;
    int nChng = 0;
    if( pWhere==0 ) return 0;
    if( pSubq->selFlags & (SF_Recursive|SF_MultiPart) ) return 0;
  
  #ifndef SQLITE_OMIT_WINDOWFUNC
    if( pSubq->pPrior ){
      Select *pSel;
      for(pSel=pSubq; pSel; pSel=pSel->pPrior){
        if( pSel->pWin ) return 0;    /* restriction (6b) */
      }
    }else{
      if( pSubq->pWin && pSubq->pWin->pPartition==0 ) return 0;
    }
  #endif
  
  #ifdef SQLITE_DEBUG
    /* Only the first term of a compound can have a WITH clause.  But make
    ** sure no other terms are marked SF_Recursive in case something changes
    ** in the future.
    */
    {
      Select *pX;  
      for(pX=pSubq; pX; pX=pX->pPrior){
        assert( (pX->selFlags & (SF_Recursive))==0 );
      }
    }
  #endif
  
    if( pSubq->pLimit!=0 ){
      return 0; /* restriction (3) */
    }
    while( pWhere->op==TK_AND ){
      nChng += pushDownWhereTerms(pParse, pSubq, pWhere->pRight,
                                  iCursor, isLeftJoin);
      pWhere = pWhere->pLeft;
    }
    if( isLeftJoin
     && (ExprHasProperty(pWhere,EP_FromJoin)==0
           || pWhere->iRightJoinTable!=iCursor)
    ){
      return 0; /* restriction (4) */
    }
    if( ExprHasProperty(pWhere,EP_FromJoin) && pWhere->iRightJoinTable!=iCursor ){
      return 0; /* restriction (5) */
    }
    if( sqlite3ExprIsTableConstant(pWhere, iCursor) ){
      nChng++;
      pSubq->selFlags |= SF_PushDown;
      while( pSubq ){
        SubstContext x;
        pNew = sqlite3ExprDup(pParse->db, pWhere, 0);
        unsetJoinExpr(pNew, -1);
        x.pParse = pParse;
        x.iTable = iCursor;
        x.iNewTable = iCursor;
        x.isLeftJoin = 0;
        x.pEList = pSubq->pEList;
        pNew = substExpr(&x, pNew);
  #ifndef SQLITE_OMIT_WINDOWFUNC
        if( pSubq->pWin && 0==pushDownWindowCheck(pParse, pSubq, pNew) ){
          /* Restriction 6c has prevented push-down in this case */
          sqlite3ExprDelete(pParse->db, pNew);
          nChng--;
          break;
        }
  #endif
        if( pSubq->selFlags & SF_Aggregate ){
          pSubq->pHaving = sqlite3ExprAnd(pParse, pSubq->pHaving, pNew);
        }else{
          pSubq->pWhere = sqlite3ExprAnd(pParse, pSubq->pWhere, pNew);
        }
        pSubq = pSubq->pPrior;
      }
    }
    return nChng;
  }
  #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */
  
  /*
  ** The pFunc is the only aggregate function in the query.  Check to see
  ** if the query is a candidate for the min/max optimization. 
  **
  ** If the query is a candidate for the min/max optimization, then set
  ** *ppMinMax to be an ORDER BY clause to be used for the optimization
  ** and return either WHERE_ORDERBY_MIN or WHERE_ORDERBY_MAX depending on
  ** whether pFunc is a min() or max() function.
  **
  ** If the query is not a candidate for the min/max optimization, return
  ** WHERE_ORDERBY_NORMAL (which must be zero).
  **
  ** This routine must be called after aggregate functions have been
  ** located but before their arguments have been subjected to aggregate
  ** analysis.
  */
  static u8 minMaxQuery(sqlite3 *db, Expr *pFunc, ExprList **ppMinMax){
    int eRet = WHERE_ORDERBY_NORMAL;      /* Return value */
    ExprList *pEList = pFunc->x.pList;    /* Arguments to agg function */
    const char *zFunc;                    /* Name of aggregate function pFunc */
    ExprList *pOrderBy;
    u8 sortFlags = 0;
  
    assert( *ppMinMax==0 );
    assert( pFunc->op==TK_AGG_FUNCTION );
    assert( !IsWindowFunc(pFunc) );
    if( pEList==0 
     || pEList->nExpr!=1
     || ExprHasProperty(pFunc, EP_WinFunc)
     || OptimizationDisabled(db, SQLITE_MinMaxOpt)
    ){
      return eRet;
    }
    zFunc = pFunc->u.zToken;
    if( sqlite3StrICmp(zFunc, "min")==0 ){
      eRet = WHERE_ORDERBY_MIN;
      if( sqlite3ExprCanBeNull(pEList->a[0].pExpr) ){
        sortFlags = KEYINFO_ORDER_BIGNULL;
      }
    }else if( sqlite3StrICmp(zFunc, "max")==0 ){
      eRet = WHERE_ORDERBY_MAX;
      sortFlags = KEYINFO_ORDER_DESC;
    }else{
      return eRet;
    }
    *ppMinMax = pOrderBy = sqlite3ExprListDup(db, pEList, 0);
    assert( pOrderBy!=0 || db->mallocFailed );
    if( pOrderBy ) pOrderBy->a[0].sortFlags = sortFlags;
    return eRet;
  }
  
  /*
  ** The select statement passed as the first argument is an aggregate query.
  ** The second argument is the associated aggregate-info object. This 
  ** function tests if the SELECT is of the form:
  **
  **   SELECT count(*) FROM <tbl>
  **
  ** where table is a database table, not a sub-select or view. If the query
  ** does match this pattern, then a pointer to the Table object representing
  ** <tbl> is returned. Otherwise, 0 is returned.
  */
  static Table *isSimpleCount(Select *p, AggInfo *pAggInfo){
    Table *pTab;
    Expr *pExpr;
  
    assert( !p->pGroupBy );
  
    if( p->pWhere || p->pEList->nExpr!=1 
     || p->pSrc->nSrc!=1 || p->pSrc->a[0].pSelect
    ){
      return 0;
    }
    pTab = p->pSrc->a[0].pTab;
    pExpr = p->pEList->a[0].pExpr;
    assert( pTab && !pTab->pSelect && pExpr );
  
    if( IsVirtual(pTab) ) return 0;
    if( pExpr->op!=TK_AGG_FUNCTION ) return 0;
    if( NEVER(pAggInfo->nFunc==0) ) return 0;
    if( (pAggInfo->aFunc[0].pFunc->funcFlags&SQLITE_FUNC_COUNT)==0 ) return 0;
    if( ExprHasProperty(pExpr, EP_Distinct|EP_WinFunc) ) return 0;
  
    return pTab;
  }
  
  /*
  ** If the source-list item passed as an argument was augmented with an
  ** INDEXED BY clause, then try to locate the specified index. If there
  ** was such a clause and the named index cannot be found, return 
  ** SQLITE_ERROR and leave an error in pParse. Otherwise, populate 
  ** pFrom->pIndex and return SQLITE_OK.
  */
  int sqlite3IndexedByLookup(Parse *pParse, SrcItem *pFrom){
    Table *pTab = pFrom->pTab;
    char *zIndexedBy = pFrom->u1.zIndexedBy;
    Index *pIdx;
    assert( pTab!=0 );
    assert( pFrom->fg.isIndexedBy!=0 );
  
    for(pIdx=pTab->pIndex; 
        pIdx && sqlite3StrICmp(pIdx->zName, zIndexedBy); 
        pIdx=pIdx->pNext
    );
    if( !pIdx ){
      sqlite3ErrorMsg(pParse, "no such index: %s", zIndexedBy, 0);
      pParse->checkSchema = 1;
      return SQLITE_ERROR;
    }
    pFrom->u2.pIBIndex = pIdx;
    return SQLITE_OK;
  }
  
  /*
  ** Detect compound SELECT statements that use an ORDER BY clause with 
  ** an alternative collating sequence.
  **
  **    SELECT ... FROM t1 EXCEPT SELECT ... FROM t2 ORDER BY .. COLLATE ...
  **
  ** These are rewritten as a subquery:
  **
  **    SELECT * FROM (SELECT ... FROM t1 EXCEPT SELECT ... FROM t2)
  **     ORDER BY ... COLLATE ...
  **
  ** This transformation is necessary because the multiSelectOrderBy() routine
  ** above that generates the code for a compound SELECT with an ORDER BY clause
  ** uses a merge algorithm that requires the same collating sequence on the
  ** result columns as on the ORDER BY clause.  See ticket
  ** http://www.sqlite.org/src/info/6709574d2a
  **
  ** This transformation is only needed for EXCEPT, INTERSECT, and UNION.
  ** The UNION ALL operator works fine with multiSelectOrderBy() even when
  ** there are COLLATE terms in the ORDER BY.
  */
  static int convertCompoundSelectToSubquery(Walker *pWalker, Select *p){
    int i;
    Select *pNew;
    Select *pX;
    sqlite3 *db;
    struct ExprList_item *a;
    SrcList *pNewSrc;
    Parse *pParse;
    Token dummy;
  
    if( p->pPrior==0 ) return WRC_Continue;
    if( p->pOrderBy==0 ) return WRC_Continue;
    for(pX=p; pX && (pX->op==TK_ALL || pX->op==TK_SELECT); pX=pX->pPrior){}
    if( pX==0 ) return WRC_Continue;
    a = p->pOrderBy->a;
  #ifndef SQLITE_OMIT_WINDOWFUNC
    /* If iOrderByCol is already non-zero, then it has already been matched
    ** to a result column of the SELECT statement. This occurs when the
    ** SELECT is rewritten for window-functions processing and then passed
    ** to sqlite3SelectPrep() and similar a second time. The rewriting done
    ** by this function is not required in this case. */
    if( a[0].u.x.iOrderByCol ) return WRC_Continue;
  #endif
    for(i=p->pOrderBy->nExpr-1; i>=0; i--){
      if( a[i].pExpr->flags & EP_Collate ) break;
    }
    if( i<0 ) return WRC_Continue;
  
    /* If we reach this point, that means the transformation is required. */
  
    pParse = pWalker->pParse;
    db = pParse->db;
    pNew = sqlite3DbMallocZero(db, sizeof(*pNew) );
    if( pNew==0 ) return WRC_Abort;
    memset(&dummy, 0, sizeof(dummy));
    pNewSrc = sqlite3SrcListAppendFromTerm(pParse,0,0,0,&dummy,pNew,0,0);
    if( pNewSrc==0 ) return WRC_Abort;
    *pNew = *p;
    p->pSrc = pNewSrc;
    p->pEList = sqlite3ExprListAppend(pParse, 0, sqlite3Expr(db, TK_ASTERISK, 0));
    p->op = TK_SELECT;
    p->pWhere = 0;
    pNew->pGroupBy = 0;
    pNew->pHaving = 0;
    pNew->pOrderBy = 0;
    p->pPrior = 0;
    p->pNext = 0;
    p->pWith = 0;
  #ifndef SQLITE_OMIT_WINDOWFUNC
    p->pWinDefn = 0;
  #endif
    p->selFlags &= ~SF_Compound;
    assert( (p->selFlags & SF_Converted)==0 );
    p->selFlags |= SF_Converted;
    assert( pNew->pPrior!=0 );
    pNew->pPrior->pNext = pNew;
    pNew->pLimit = 0;
    return WRC_Continue;
  }
  
  /*
  ** Check to see if the FROM clause term pFrom has table-valued function
  ** arguments.  If it does, leave an error message in pParse and return
  ** non-zero, since pFrom is not allowed to be a table-valued function.
  */
  static int cannotBeFunction(Parse *pParse, SrcItem *pFrom){
    if( pFrom->fg.isTabFunc ){
      sqlite3ErrorMsg(pParse, "'%s' is not a function", pFrom->zName);
      return 1;
    }
    return 0;
  }
  
  #ifndef SQLITE_OMIT_CTE
  /*
  ** Argument pWith (which may be NULL) points to a linked list of nested 
  ** WITH contexts, from inner to outermost. If the table identified by 
  ** FROM clause element pItem is really a common-table-expression (CTE) 
  ** then return a pointer to the CTE definition for that table. Otherwise
  ** return NULL.
  **
  ** If a non-NULL value is returned, set *ppContext to point to the With
  ** object that the returned CTE belongs to.
  */
  static struct Cte *searchWith(
    With *pWith,                    /* Current innermost WITH clause */
    SrcItem *pItem,                 /* FROM clause element to resolve */
    With **ppContext                /* OUT: WITH clause return value belongs to */
  ){
    const char *zName = pItem->zName;
    With *p;
    assert( pItem->zDatabase==0 );
    assert( zName!=0 );
    for(p=pWith; p; p=p->pOuter){
      int i;
      for(i=0; i<p->nCte; i++){
        if( sqlite3StrICmp(zName, p->a[i].zName)==0 ){
          *ppContext = p;
          return &p->a[i];
        }
      }
      if( p->bView ) break;
    }
    return 0;
  }
  
  /* The code generator maintains a stack of active WITH clauses
  ** with the inner-most WITH clause being at the top of the stack.
  **
  ** This routine pushes the WITH clause passed as the second argument
  ** onto the top of the stack. If argument bFree is true, then this
  ** WITH clause will never be popped from the stack but should instead
  ** be freed along with the Parse object. In other cases, when
  ** bFree==0, the With object will be freed along with the SELECT 
  ** statement with which it is associated.
  **
  ** This routine returns a copy of pWith.  Or, if bFree is true and
  ** the pWith object is destroyed immediately due to an OOM condition,
  ** then this routine return NULL.
  **
  ** If bFree is true, do not continue to use the pWith pointer after
  ** calling this routine,  Instead, use only the return value.
  */
  With *sqlite3WithPush(Parse *pParse, With *pWith, u8 bFree){
    if( pWith ){
      if( bFree ){
        pWith = (With*)sqlite3ParserAddCleanup(pParse, 
                        (void(*)(sqlite3*,void*))sqlite3WithDelete,
                        pWith);
        if( pWith==0 ) return 0;
      }
      if( pParse->nErr==0 ){
        assert( pParse->pWith!=pWith );
        pWith->pOuter = pParse->pWith;
        pParse->pWith = pWith;
      }
    }
    return pWith;
  }
  
  /*
  ** This function checks if argument pFrom refers to a CTE declared by 
  ** a WITH clause on the stack currently maintained by the parser (on the
  ** pParse->pWith linked list).  And if currently processing a CTE
  ** CTE expression, through routine checks to see if the reference is
  ** a recursive reference to the CTE.
  **
  ** If pFrom matches a CTE according to either of these two above, pFrom->pTab
  ** and other fields are populated accordingly.
  **
  ** Return 0 if no match is found. 
  ** Return 1 if a match is found.
  ** Return 2 if an error condition is detected.
  */
  static int resolveFromTermToCte(
    Parse *pParse,                  /* The parsing context */
    Walker *pWalker,                /* Current tree walker */
    SrcItem *pFrom                  /* The FROM clause term to check */
  ){
    Cte *pCte;               /* Matched CTE (or NULL if no match) */
    With *pWith;             /* The matching WITH */
  
    assert( pFrom->pTab==0 );
    if( pParse->pWith==0 ){
      /* There are no WITH clauses in the stack.  No match is possible */
      return 0;
    }
    if( pParse->nErr ){
      /* Prior errors might have left pParse->pWith in a goofy state, so
      ** go no further. */
      return 0;
    }
    if( pFrom->zDatabase!=0 ){
      /* The FROM term contains a schema qualifier (ex: main.t1) and so
      ** it cannot possibly be a CTE reference. */
      return 0;
    }
    if( pFrom->fg.notCte ){
      /* The FROM term is specifically excluded from matching a CTE.
      **   (1)  It is part of a trigger that used to have zDatabase but had
      **        zDatabase removed by sqlite3FixTriggerStep().
      **   (2)  This is the first term in the FROM clause of an UPDATE.
      */
      return 0;
    }
    pCte = searchWith(pParse->pWith, pFrom, &pWith);
    if( pCte ){
      sqlite3 *db = pParse->db;
      Table *pTab;
      ExprList *pEList;
      Select *pSel;
      Select *pLeft;                /* Left-most SELECT statement */
      Select *pRecTerm;             /* Left-most recursive term */
      int bMayRecursive;            /* True if compound joined by UNION [ALL] */
      With *pSavedWith;             /* Initial value of pParse->pWith */
      int iRecTab = -1;             /* Cursor for recursive table */
      CteUse *pCteUse;
  
      /* If pCte->zCteErr is non-NULL at this point, then this is an illegal
      ** recursive reference to CTE pCte. Leave an error in pParse and return
      ** early. If pCte->zCteErr is NULL, then this is not a recursive reference.
      ** In this case, proceed.  */
      if( pCte->zCteErr ){
        sqlite3ErrorMsg(pParse, pCte->zCteErr, pCte->zName);
        return 2;
      }
      if( cannotBeFunction(pParse, pFrom) ) return 2;
  
      assert( pFrom->pTab==0 );
      pTab = sqlite3DbMallocZero(db, sizeof(Table));
      if( pTab==0 ) return 2;
      pCteUse = pCte->pUse;
      if( pCteUse==0 ){
        pCte->pUse = pCteUse = sqlite3DbMallocZero(db, sizeof(pCteUse[0]));
        if( pCteUse==0
         || sqlite3ParserAddCleanup(pParse,sqlite3DbFree,pCteUse)==0
        ){
          sqlite3DbFree(db, pTab);
          return 2;
        }
        pCteUse->eM10d = pCte->eM10d;
      }
      pFrom->pTab = pTab;
      pTab->nTabRef = 1;
      pTab->zName = sqlite3DbStrDup(db, pCte->zName);
      pTab->iPKey = -1;
      pTab->nRowLogEst = 200; assert( 200==sqlite3LogEst(1048576) );
      pTab->tabFlags |= TF_Ephemeral | TF_NoVisibleRowid;
      pFrom->pSelect = sqlite3SelectDup(db, pCte->pSelect, 0);
      if( db->mallocFailed ) return 2;
      pFrom->pSelect->selFlags |= SF_CopyCte;
      assert( pFrom->pSelect );
      pFrom->fg.isCte = 1;
      pFrom->u2.pCteUse = pCteUse;
      pCteUse->nUse++;
      if( pCteUse->nUse>=2 && pCteUse->eM10d==M10d_Any ){
        pCteUse->eM10d = M10d_Yes;
      }
  
      /* Check if this is a recursive CTE. */
      pRecTerm = pSel = pFrom->pSelect;
      bMayRecursive = ( pSel->op==TK_ALL || pSel->op==TK_UNION );
      while( bMayRecursive && pRecTerm->op==pSel->op ){
        int i;
        SrcList *pSrc = pRecTerm->pSrc;
        assert( pRecTerm->pPrior!=0 );
        for(i=0; i<pSrc->nSrc; i++){
          SrcItem *pItem = &pSrc->a[i];
          if( pItem->zDatabase==0 
           && pItem->zName!=0 
           && 0==sqlite3StrICmp(pItem->zName, pCte->zName)
          ){
            pItem->pTab = pTab;
            pTab->nTabRef++;
            pItem->fg.isRecursive = 1;
            if( pRecTerm->selFlags & SF_Recursive ){
              sqlite3ErrorMsg(pParse,
                 "multiple references to recursive table: %s", pCte->zName
              );
              return 2;
            }
            pRecTerm->selFlags |= SF_Recursive;
            if( iRecTab<0 ) iRecTab = pParse->nTab++;
            pItem->iCursor = iRecTab;
          }
        }
        if( (pRecTerm->selFlags & SF_Recursive)==0 ) break;
        pRecTerm = pRecTerm->pPrior;
      }
  
      pCte->zCteErr = "circular reference: %s";
      pSavedWith = pParse->pWith;
      pParse->pWith = pWith;
      if( pSel->selFlags & SF_Recursive ){
        int rc;
        assert( pRecTerm!=0 );
        assert( (pRecTerm->selFlags & SF_Recursive)==0 );
        assert( pRecTerm->pNext!=0 );
        assert( (pRecTerm->pNext->selFlags & SF_Recursive)!=0 );
        assert( pRecTerm->pWith==0 );
        pRecTerm->pWith = pSel->pWith;
        rc = sqlite3WalkSelect(pWalker, pRecTerm);
        pRecTerm->pWith = 0;
        if( rc ){
          pParse->pWith = pSavedWith;
          return 2;
        }
      }else{
        if( sqlite3WalkSelect(pWalker, pSel) ){
          pParse->pWith = pSavedWith;
          return 2;
        }
      }
      pParse->pWith = pWith;
  
      for(pLeft=pSel; pLeft->pPrior; pLeft=pLeft->pPrior);
      pEList = pLeft->pEList;
      if( pCte->pCols ){
        if( pEList && pEList->nExpr!=pCte->pCols->nExpr ){
          sqlite3ErrorMsg(pParse, "table %s has %d values for %d columns",
              pCte->zName, pEList->nExpr, pCte->pCols->nExpr
          );
          pParse->pWith = pSavedWith;
          return 2;
        }
        pEList = pCte->pCols;
      }
  
      sqlite3ColumnsFromExprList(pParse, pEList, &pTab->nCol, &pTab->aCol);
      if( bMayRecursive ){
        if( pSel->selFlags & SF_Recursive ){
          pCte->zCteErr = "multiple recursive references: %s";
        }else{
          pCte->zCteErr = "recursive reference in a subquery: %s";
        }
        sqlite3WalkSelect(pWalker, pSel);
      }
      pCte->zCteErr = 0;
      pParse->pWith = pSavedWith;
      return 1;  /* Success */
    }
    return 0;  /* No match */
  }
  #endif
  
  #ifndef SQLITE_OMIT_CTE
  /*
  ** If the SELECT passed as the second argument has an associated WITH 
  ** clause, pop it from the stack stored as part of the Parse object.
  **
  ** This function is used as the xSelectCallback2() callback by
  ** sqlite3SelectExpand() when walking a SELECT tree to resolve table
  ** names and other FROM clause elements. 
  */
  void sqlite3SelectPopWith(Walker *pWalker, Select *p){
    Parse *pParse = pWalker->pParse;
    if( OK_IF_ALWAYS_TRUE(pParse->pWith) && p->pPrior==0 ){
      With *pWith = findRightmost(p)->pWith;
      if( pWith!=0 ){
        assert( pParse->pWith==pWith || pParse->nErr );
        pParse->pWith = pWith->pOuter;
      }
    }
  }
  #endif
  
  /*
  ** The SrcList_item structure passed as the second argument represents a
  ** sub-query in the FROM clause of a SELECT statement. This function
  ** allocates and populates the SrcList_item.pTab object. If successful,
  ** SQLITE_OK is returned. Otherwise, if an OOM error is encountered,
  ** SQLITE_NOMEM.
  */
  int sqlite3ExpandSubquery(Parse *pParse, SrcItem *pFrom){
    Select *pSel = pFrom->pSelect;
    Table *pTab;
  
    assert( pSel );
    pFrom->pTab = pTab = sqlite3DbMallocZero(pParse->db, sizeof(Table));
    if( pTab==0 ) return SQLITE_NOMEM;
    pTab->nTabRef = 1;
    if( pFrom->zAlias ){
      pTab->zName = sqlite3DbStrDup(pParse->db, pFrom->zAlias);
    }else{
      pTab->zName = sqlite3MPrintf(pParse->db, "subquery_%u", pSel->selId);
    }
    while( pSel->pPrior ){ pSel = pSel->pPrior; }
    sqlite3ColumnsFromExprList(pParse, pSel->pEList,&pTab->nCol,&pTab->aCol);
    pTab->iPKey = -1;
    pTab->nRowLogEst = 200; assert( 200==sqlite3LogEst(1048576) );
  #ifndef SQLITE_ALLOW_ROWID_IN_VIEW
    /* The usual case - do not allow ROWID on a subquery */
    pTab->tabFlags |= TF_Ephemeral | TF_NoVisibleRowid;
  #else
    pTab->tabFlags |= TF_Ephemeral;  /* Legacy compatibility mode */
  #endif
  
  
    return pParse->nErr ? SQLITE_ERROR : SQLITE_OK;
  }
  
  /*
  ** This routine is a Walker callback for "expanding" a SELECT statement.
  ** "Expanding" means to do the following:
  **
  **    (1)  Make sure VDBE cursor numbers have been assigned to every
  **         element of the FROM clause.
  **
  **    (2)  Fill in the pTabList->a[].pTab fields in the SrcList that 
  **         defines FROM clause.  When views appear in the FROM clause,
  **         fill pTabList->a[].pSelect with a copy of the SELECT statement
  **         that implements the view.  A copy is made of the view's SELECT
  **         statement so that we can freely modify or delete that statement
  **         without worrying about messing up the persistent representation
  **         of the view.
  **
  **    (3)  Add terms to the WHERE clause to accommodate the NATURAL keyword
  **         on joins and the ON and USING clause of joins.
  **
  **    (4)  Scan the list of columns in the result set (pEList) looking
  **         for instances of the "*" operator or the TABLE.* operator.
  **         If found, expand each "*" to be every column in every table
  **         and TABLE.* to be every column in TABLE.
  **
  */
  static int selectExpander(Walker *pWalker, Select *p){
    Parse *pParse = pWalker->pParse;
    int i, j, k, rc;
    SrcList *pTabList;
    ExprList *pEList;
    SrcItem *pFrom;
    sqlite3 *db = pParse->db;
    Expr *pE, *pRight, *pExpr;
    u16 selFlags = p->selFlags;
    u32 elistFlags = 0;
  
    p->selFlags |= SF_Expanded;
    if( db->mallocFailed  ){
      return WRC_Abort;
    }
    assert( p->pSrc!=0 );
    if( (selFlags & SF_Expanded)!=0 ){
      return WRC_Prune;
    }
    if( pWalker->eCode ){
      /* Renumber selId because it has been copied from a view */
      p->selId = ++pParse->nSelect;
    }
    pTabList = p->pSrc;
    pEList = p->pEList;
    if( pParse->pWith && (p->selFlags & SF_View) ){
      if( p->pWith==0 ){
        p->pWith = (With*)sqlite3DbMallocZero(db, sizeof(With));
        if( p->pWith==0 ){
          return WRC_Abort;
        }
      }
      p->pWith->bView = 1;
    }
    sqlite3WithPush(pParse, p->pWith, 0);
  
    /* Make sure cursor numbers have been assigned to all entries in
    ** the FROM clause of the SELECT statement.
    */
    sqlite3SrcListAssignCursors(pParse, pTabList);
  
    /* Look up every table named in the FROM clause of the select.  If
    ** an entry of the FROM clause is a subquery instead of a table or view,
    ** then create a transient table structure to describe the subquery.
    */
    for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
      Table *pTab;
      assert( pFrom->fg.isRecursive==0 || pFrom->pTab!=0 );
      if( pFrom->pTab ) continue;
      assert( pFrom->fg.isRecursive==0 );
      if( pFrom->zName==0 ){
  #ifndef SQLITE_OMIT_SUBQUERY
        Select *pSel = pFrom->pSelect;
        /* A sub-query in the FROM clause of a SELECT */
        assert( pSel!=0 );
        assert( pFrom->pTab==0 );
        if( sqlite3WalkSelect(pWalker, pSel) ) return WRC_Abort;
        if( sqlite3ExpandSubquery(pParse, pFrom) ) return WRC_Abort;
  #endif
  #ifndef SQLITE_OMIT_CTE
      }else if( (rc = resolveFromTermToCte(pParse, pWalker, pFrom))!=0 ){
        if( rc>1 ) return WRC_Abort;
        pTab = pFrom->pTab;
        assert( pTab!=0 );
  #endif
      }else{
        /* An ordinary table or view name in the FROM clause */
        assert( pFrom->pTab==0 );
        pFrom->pTab = pTab = sqlite3LocateTableItem(pParse, 0, pFrom);
        if( pTab==0 ) return WRC_Abort;
        if( pTab->nTabRef>=0xffff ){
          sqlite3ErrorMsg(pParse, "too many references to \"%s\": max 65535",
             pTab->zName);
          pFrom->pTab = 0;
          return WRC_Abort;
        }
        pTab->nTabRef++;
        if( !IsVirtual(pTab) && cannotBeFunction(pParse, pFrom) ){
          return WRC_Abort;
        }
  #if !defined(SQLITE_OMIT_VIEW) || !defined(SQLITE_OMIT_VIRTUALTABLE)
        if( IsVirtual(pTab) || pTab->pSelect ){
          i16 nCol;
          u8 eCodeOrig = pWalker->eCode;
          if( sqlite3ViewGetColumnNames(pParse, pTab) ) return WRC_Abort;
          assert( pFrom->pSelect==0 );
          if( pTab->pSelect
           && (db->flags & SQLITE_EnableView)==0
           && pTab->pSchema!=db->aDb[1].pSchema
          ){
            sqlite3ErrorMsg(pParse, "access to view \"%s\" prohibited",
              pTab->zName);
          }
  #ifndef SQLITE_OMIT_VIRTUALTABLE
          assert( SQLITE_VTABRISK_Normal==1 && SQLITE_VTABRISK_High==2 );
          if( IsVirtual(pTab)
           && pFrom->fg.fromDDL
           && ALWAYS(pTab->pVTable!=0)
           && pTab->pVTable->eVtabRisk > ((db->flags & SQLITE_TrustedSchema)!=0)
          ){
            sqlite3ErrorMsg(pParse, "unsafe use of virtual table \"%s\"",
                                    pTab->zName);
          }
  #endif
          pFrom->pSelect = sqlite3SelectDup(db, pTab->pSelect, 0);
          nCol = pTab->nCol;
          pTab->nCol = -1;
          pWalker->eCode = 1;  /* Turn on Select.selId renumbering */
          sqlite3WalkSelect(pWalker, pFrom->pSelect);
          pWalker->eCode = eCodeOrig;
          pTab->nCol = nCol;
        }
  #endif
      }
  
      /* Locate the index named by the INDEXED BY clause, if any. */
      if( pFrom->fg.isIndexedBy && sqlite3IndexedByLookup(pParse, pFrom) ){
        return WRC_Abort;
      }
    }
  
    /* Process NATURAL keywords, and ON and USING clauses of joins.
    */
    if( pParse->nErr || db->mallocFailed || sqliteProcessJoin(pParse, p) ){
      return WRC_Abort;
    }
  
    /* For every "*" that occurs in the column list, insert the names of
    ** all columns in all tables.  And for every TABLE.* insert the names
    ** of all columns in TABLE.  The parser inserted a special expression
    ** with the TK_ASTERISK operator for each "*" that it found in the column
    ** list.  The following code just has to locate the TK_ASTERISK
    ** expressions and expand each one to the list of all columns in
    ** all tables.
    **
    ** The first loop just checks to see if there are any "*" operators
    ** that need expanding.
    */
    for(k=0; k<pEList->nExpr; k++){
      pE = pEList->a[k].pExpr;
      if( pE->op==TK_ASTERISK ) break;
      assert( pE->op!=TK_DOT || pE->pRight!=0 );
      assert( pE->op!=TK_DOT || (pE->pLeft!=0 && pE->pLeft->op==TK_ID) );
      if( pE->op==TK_DOT && pE->pRight->op==TK_ASTERISK ) break;
      elistFlags |= pE->flags;
    }
    if( k<pEList->nExpr ){
      /*
      ** If we get here it means the result set contains one or more "*"
      ** operators that need to be expanded.  Loop through each expression
      ** in the result set and expand them one by one.
      */
      struct ExprList_item *a = pEList->a;
      ExprList *pNew = 0;
      int flags = pParse->db->flags;
      int longNames = (flags & SQLITE_FullColNames)!=0
                        && (flags & SQLITE_ShortColNames)==0;
  
      for(k=0; k<pEList->nExpr; k++){
        pE = a[k].pExpr;
        elistFlags |= pE->flags;
        pRight = pE->pRight;
        assert( pE->op!=TK_DOT || pRight!=0 );
        if( pE->op!=TK_ASTERISK
         && (pE->op!=TK_DOT || pRight->op!=TK_ASTERISK)
        ){
          /* This particular expression does not need to be expanded.
          */
          pNew = sqlite3ExprListAppend(pParse, pNew, a[k].pExpr);
          if( pNew ){
            pNew->a[pNew->nExpr-1].zEName = a[k].zEName;
            pNew->a[pNew->nExpr-1].eEName = a[k].eEName;
            a[k].zEName = 0;
          }
          a[k].pExpr = 0;
        }else{
          /* This expression is a "*" or a "TABLE.*" and needs to be
          ** expanded. */
          int tableSeen = 0;      /* Set to 1 when TABLE matches */
          char *zTName = 0;       /* text of name of TABLE */
          if( pE->op==TK_DOT ){
            assert( pE->pLeft!=0 );
            assert( !ExprHasProperty(pE->pLeft, EP_IntValue) );
            zTName = pE->pLeft->u.zToken;
          }
          for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
            Table *pTab = pFrom->pTab;
            Select *pSub = pFrom->pSelect;
            char *zTabName = pFrom->zAlias;
            const char *zSchemaName = 0;
            int iDb;
            if( zTabName==0 ){
              zTabName = pTab->zName;
            }
            if( db->mallocFailed ) break;
            if( pSub==0 || (pSub->selFlags & SF_NestedFrom)==0 ){
              pSub = 0;
              if( zTName && sqlite3StrICmp(zTName, zTabName)!=0 ){
                continue;
              }
              iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
              zSchemaName = iDb>=0 ? db->aDb[iDb].zDbSName : "*";
            }
            for(j=0; j<pTab->nCol; j++){
              char *zName = pTab->aCol[j].zName;
              char *zColname;  /* The computed column name */
              char *zToFree;   /* Malloced string that needs to be freed */
              Token sColname;  /* Computed column name as a token */
  
              assert( zName );
              if( zTName && pSub
               && sqlite3MatchEName(&pSub->pEList->a[j], 0, zTName, 0)==0
              ){
                continue;
              }
  
              /* If a column is marked as 'hidden', omit it from the expanded
              ** result-set list unless the SELECT has the SF_IncludeHidden
              ** bit set.
              */
              if( (p->selFlags & SF_IncludeHidden)==0
               && IsHiddenColumn(&pTab->aCol[j]) 
              ){
                continue;
              }
              tableSeen = 1;
  
              if( i>0 && zTName==0 ){
                if( (pFrom->fg.jointype & JT_NATURAL)!=0
                  && tableAndColumnIndex(pTabList, i, zName, 0, 0, 1)
                ){
                  /* In a NATURAL join, omit the join columns from the 
                  ** table to the right of the join */
                  continue;
                }
                if( sqlite3IdListIndex(pFrom->pUsing, zName)>=0 ){
                  /* In a join with a USING clause, omit columns in the
                  ** using clause from the table on the right. */
                  continue;
                }
              }
              pRight = sqlite3Expr(db, TK_ID, zName);
              zColname = zName;
              zToFree = 0;
              if( longNames || pTabList->nSrc>1 ){
                Expr *pLeft;
                pLeft = sqlite3Expr(db, TK_ID, zTabName);
                pExpr = sqlite3PExpr(pParse, TK_DOT, pLeft, pRight);
                if( zSchemaName ){
                  pLeft = sqlite3Expr(db, TK_ID, zSchemaName);
                  pExpr = sqlite3PExpr(pParse, TK_DOT, pLeft, pExpr);
                }
                if( longNames ){
                  zColname = sqlite3MPrintf(db, "%s.%s", zTabName, zName);
                  zToFree = zColname;
                }
              }else{
                pExpr = pRight;
              }
              pNew = sqlite3ExprListAppend(pParse, pNew, pExpr);
              sqlite3TokenInit(&sColname, zColname);
              sqlite3ExprListSetName(pParse, pNew, &sColname, 0);
              if( pNew && (p->selFlags & SF_NestedFrom)!=0 && !IN_RENAME_OBJECT ){
                struct ExprList_item *pX = &pNew->a[pNew->nExpr-1];
                sqlite3DbFree(db, pX->zEName);
                if( pSub ){
                  pX->zEName = sqlite3DbStrDup(db, pSub->pEList->a[j].zEName);
                  testcase( pX->zEName==0 );
                }else{
                  pX->zEName = sqlite3MPrintf(db, "%s.%s.%s",
                                             zSchemaName, zTabName, zColname);
                  testcase( pX->zEName==0 );
                }
                pX->eEName = ENAME_TAB;
              }
              sqlite3DbFree(db, zToFree);
            }
          }
          if( !tableSeen ){
            if( zTName ){
              sqlite3ErrorMsg(pParse, "no such table: %s", zTName);
            }else{
              sqlite3ErrorMsg(pParse, "no tables specified");
            }
          }
        }
      }
      sqlite3ExprListDelete(db, pEList);
      p->pEList = pNew;
    }
    if( p->pEList ){
      if( p->pEList->nExpr>db->aLimit[SQLITE_LIMIT_COLUMN] ){
        sqlite3ErrorMsg(pParse, "too many columns in result set");
        return WRC_Abort;
      }
      if( (elistFlags & (EP_HasFunc|EP_Subquery))!=0 ){
        p->selFlags |= SF_ComplexResult;
      }
    }
    return WRC_Continue;
  }
  
  #if SQLITE_DEBUG
  /*
  ** Always assert.  This xSelectCallback2 implementation proves that the
  ** xSelectCallback2 is never invoked.
  */
  void sqlite3SelectWalkAssert2(Walker *NotUsed, Select *NotUsed2){
    UNUSED_PARAMETER2(NotUsed, NotUsed2);
    assert( 0 );
  }
  #endif
  /*
  ** This routine "expands" a SELECT statement and all of its subqueries.
  ** For additional information on what it means to "expand" a SELECT
  ** statement, see the comment on the selectExpand worker callback above.
  **
  ** Expanding a SELECT statement is the first step in processing a
  ** SELECT statement.  The SELECT statement must be expanded before
  ** name resolution is performed.
  **
  ** If anything goes wrong, an error message is written into pParse.
  ** The calling function can detect the problem by looking at pParse->nErr
  ** and/or pParse->db->mallocFailed.
  */
  static void sqlite3SelectExpand(Parse *pParse, Select *pSelect){
    Walker w;
    w.xExprCallback = sqlite3ExprWalkNoop;
    w.pParse = pParse;
    if( OK_IF_ALWAYS_TRUE(pParse->hasCompound) ){
      w.xSelectCallback = convertCompoundSelectToSubquery;
      w.xSelectCallback2 = 0;
      sqlite3WalkSelect(&w, pSelect);
    }
    w.xSelectCallback = selectExpander;
    w.xSelectCallback2 = sqlite3SelectPopWith;
    w.eCode = 0;
    sqlite3WalkSelect(&w, pSelect);
  }
  
  
  #ifndef SQLITE_OMIT_SUBQUERY
  /*
  ** This is a Walker.xSelectCallback callback for the sqlite3SelectTypeInfo()
  ** interface.
  **
  ** For each FROM-clause subquery, add Column.zType and Column.zColl
  ** information to the Table structure that represents the result set
  ** of that subquery.
  **
  ** The Table structure that represents the result set was constructed
  ** by selectExpander() but the type and collation information was omitted
  ** at that point because identifiers had not yet been resolved.  This
  ** routine is called after identifier resolution.
  */
  static void selectAddSubqueryTypeInfo(Walker *pWalker, Select *p){
    Parse *pParse;
    int i;
    SrcList *pTabList;
    SrcItem *pFrom;
  
    assert( p->selFlags & SF_Resolved );
    if( p->selFlags & SF_HasTypeInfo ) return;
    p->selFlags |= SF_HasTypeInfo;
    pParse = pWalker->pParse;
    pTabList = p->pSrc;
    for(i=0, pFrom=pTabList->a; i<pTabList->nSrc; i++, pFrom++){
      Table *pTab = pFrom->pTab;
      assert( pTab!=0 );
      if( (pTab->tabFlags & TF_Ephemeral)!=0 ){
        /* A sub-query in the FROM clause of a SELECT */
        Select *pSel = pFrom->pSelect;
        if( pSel ){
          while( pSel->pPrior ) pSel = pSel->pPrior;
          sqlite3SelectAddColumnTypeAndCollation(pParse, pTab, pSel,
                                                 SQLITE_AFF_NONE);
        }
      }
    }
  }
  #endif
  
  
  /*
  ** This routine adds datatype and collating sequence information to
  ** the Table structures of all FROM-clause subqueries in a
  ** SELECT statement.
  **
  ** Use this routine after name resolution.
  */
  static void sqlite3SelectAddTypeInfo(Parse *pParse, Select *pSelect){
  #ifndef SQLITE_OMIT_SUBQUERY
    Walker w;
    w.xSelectCallback = sqlite3SelectWalkNoop;
    w.xSelectCallback2 = selectAddSubqueryTypeInfo;
    w.xExprCallback = sqlite3ExprWalkNoop;
    w.pParse = pParse;
    sqlite3WalkSelect(&w, pSelect);
  #endif
  }
  
  
  /*
  ** This routine sets up a SELECT statement for processing.  The
  ** following is accomplished:
  **
  **     *  VDBE Cursor numbers are assigned to all FROM-clause terms.
  **     *  Ephemeral Table objects are created for all FROM-clause subqueries.
  **     *  ON and USING clauses are shifted into WHERE statements
  **     *  Wildcards "*" and "TABLE.*" in result sets are expanded.
  **     *  Identifiers in expression are matched to tables.
  **
  ** This routine acts recursively on all subqueries within the SELECT.
  */
  void sqlite3SelectPrep(
    Parse *pParse,         /* The parser context */
    Select *p,             /* The SELECT statement being coded. */
    NameContext *pOuterNC  /* Name context for container */
  ){
    assert( p!=0 || pParse->db->mallocFailed );
    if( pParse->db->mallocFailed ) return;
    if( p->selFlags & SF_HasTypeInfo ) return;
    sqlite3SelectExpand(pParse, p);
    if( pParse->nErr || pParse->db->mallocFailed ) return;
    sqlite3ResolveSelectNames(pParse, p, pOuterNC);
    if( pParse->nErr || pParse->db->mallocFailed ) return;
    sqlite3SelectAddTypeInfo(pParse, p);
  }
  
  /*
  ** Reset the aggregate accumulator.
  **
  ** The aggregate accumulator is a set of memory cells that hold
  ** intermediate results while calculating an aggregate.  This
  ** routine generates code that stores NULLs in all of those memory
  ** cells.
  */
  static void resetAccumulator(Parse *pParse, AggInfo *pAggInfo){
    Vdbe *v = pParse->pVdbe;
    int i;
    struct AggInfo_func *pFunc;
    int nReg = pAggInfo->nFunc + pAggInfo->nColumn;
    if( nReg==0 ) return;
    if( pParse->nErr || pParse->db->mallocFailed ) return;
  #ifdef SQLITE_DEBUG
    /* Verify that all AggInfo registers are within the range specified by
    ** AggInfo.mnReg..AggInfo.mxReg */
    assert( nReg==pAggInfo->mxReg-pAggInfo->mnReg+1 );
    for(i=0; i<pAggInfo->nColumn; i++){
      assert( pAggInfo->aCol[i].iMem>=pAggInfo->mnReg
           && pAggInfo->aCol[i].iMem<=pAggInfo->mxReg );
    }
    for(i=0; i<pAggInfo->nFunc; i++){
      assert( pAggInfo->aFunc[i].iMem>=pAggInfo->mnReg
           && pAggInfo->aFunc[i].iMem<=pAggInfo->mxReg );
    }
  #endif
    sqlite3VdbeAddOp3(v, OP_Null, 0, pAggInfo->mnReg, pAggInfo->mxReg);
    for(pFunc=pAggInfo->aFunc, i=0; i<pAggInfo->nFunc; i++, pFunc++){
      if( pFunc->iDistinct>=0 ){
        Expr *pE = pFunc->pFExpr;
        assert( !ExprHasProperty(pE, EP_xIsSelect) );
        if( pE->x.pList==0 || pE->x.pList->nExpr!=1 ){
          sqlite3ErrorMsg(pParse, "DISTINCT aggregates must have exactly one "
             "argument");
          pFunc->iDistinct = -1;
        }else{
          KeyInfo *pKeyInfo = sqlite3KeyInfoFromExprList(pParse, pE->x.pList,0,0);
          pFunc->iDistAddr = sqlite3VdbeAddOp4(v, OP_OpenEphemeral, 
              pFunc->iDistinct, 0, 0, (char*)pKeyInfo, P4_KEYINFO);
          ExplainQueryPlan((pParse, 0, "USE TEMP B-TREE FOR %s(DISTINCT)",
                            pFunc->pFunc->zName));
        }
      }
    }
  }
  
  /*
  ** Invoke the OP_AggFinalize opcode for every aggregate function
  ** in the AggInfo structure.
  */
  static void finalizeAggFunctions(Parse *pParse, AggInfo *pAggInfo){
    Vdbe *v = pParse->pVdbe;
    int i;
    struct AggInfo_func *pF;
    for(i=0, pF=pAggInfo->aFunc; i<pAggInfo->nFunc; i++, pF++){
      ExprList *pList = pF->pFExpr->x.pList;
      assert( !ExprHasProperty(pF->pFExpr, EP_xIsSelect) );
      sqlite3VdbeAddOp2(v, OP_AggFinal, pF->iMem, pList ? pList->nExpr : 0);
      sqlite3VdbeAppendP4(v, pF->pFunc, P4_FUNCDEF);
    }
  }
  
  
  /*
  ** Update the accumulator memory cells for an aggregate based on
  ** the current cursor position.
  **
  ** If regAcc is non-zero and there are no min() or max() aggregates
  ** in pAggInfo, then only populate the pAggInfo->nAccumulator accumulator
  ** registers if register regAcc contains 0. The caller will take care
  ** of setting and clearing regAcc.
  */
  static void updateAccumulator(
    Parse *pParse, 
    int regAcc, 
    AggInfo *pAggInfo,
    int eDistinctType
  ){
    Vdbe *v = pParse->pVdbe;
    int i;
    int regHit = 0;
    int addrHitTest = 0;
    struct AggInfo_func *pF;
    struct AggInfo_col *pC;
  
    pAggInfo->directMode = 1;
    for(i=0, pF=pAggInfo->aFunc; i<pAggInfo->nFunc; i++, pF++){
      int nArg;
      int addrNext = 0;
      int regAgg;
      ExprList *pList = pF->pFExpr->x.pList;
      assert( !ExprHasProperty(pF->pFExpr, EP_xIsSelect) );
      assert( !IsWindowFunc(pF->pFExpr) );
      if( ExprHasProperty(pF->pFExpr, EP_WinFunc) ){
        Expr *pFilter = pF->pFExpr->y.pWin->pFilter;
        if( pAggInfo->nAccumulator 
         && (pF->pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL) 
         && regAcc
        ){
          /* If regAcc==0, there there exists some min() or max() function
          ** without a FILTER clause that will ensure the magnet registers
          ** are populated. */
          if( regHit==0 ) regHit = ++pParse->nMem;
          /* If this is the first row of the group (regAcc contains 0), clear the
          ** "magnet" register regHit so that the accumulator registers
          ** are populated if the FILTER clause jumps over the the 
          ** invocation of min() or max() altogether. Or, if this is not
          ** the first row (regAcc contains 1), set the magnet register so that
          ** the accumulators are not populated unless the min()/max() is invoked
          ** and indicates that they should be.  */
          sqlite3VdbeAddOp2(v, OP_Copy, regAcc, regHit);
        }
        addrNext = sqlite3VdbeMakeLabel(pParse);
        sqlite3ExprIfFalse(pParse, pFilter, addrNext, SQLITE_JUMPIFNULL);
      }
      if( pList ){
        nArg = pList->nExpr;
        regAgg = sqlite3GetTempRange(pParse, nArg);
        sqlite3ExprCodeExprList(pParse, pList, regAgg, 0, SQLITE_ECEL_DUP);
      }else{
        nArg = 0;
        regAgg = 0;
      }
      if( pF->iDistinct>=0 && pList ){
        if( addrNext==0 ){ 
          addrNext = sqlite3VdbeMakeLabel(pParse);
        }
        pF->iDistinct = codeDistinct(pParse, eDistinctType, 
            pF->iDistinct, addrNext, pList, regAgg);
      }
      if( pF->pFunc->funcFlags & SQLITE_FUNC_NEEDCOLL ){
        CollSeq *pColl = 0;
        struct ExprList_item *pItem;
        int j;
        assert( pList!=0 );  /* pList!=0 if pF->pFunc has NEEDCOLL */
        for(j=0, pItem=pList->a; !pColl && j<nArg; j++, pItem++){
          pColl = sqlite3ExprCollSeq(pParse, pItem->pExpr);
        }
        if( !pColl ){
          pColl = pParse->db->pDfltColl;
        }
        if( regHit==0 && pAggInfo->nAccumulator ) regHit = ++pParse->nMem;
        sqlite3VdbeAddOp4(v, OP_CollSeq, regHit, 0, 0, (char *)pColl, P4_COLLSEQ);
      }
      sqlite3VdbeAddOp3(v, OP_AggStep, 0, regAgg, pF->iMem);
      sqlite3VdbeAppendP4(v, pF->pFunc, P4_FUNCDEF);
      sqlite3VdbeChangeP5(v, (u8)nArg);
      sqlite3ReleaseTempRange(pParse, regAgg, nArg);
      if( addrNext ){
        sqlite3VdbeResolveLabel(v, addrNext);
      }
    }
    if( regHit==0 && pAggInfo->nAccumulator ){
      regHit = regAcc;
    }
    if( regHit ){
      addrHitTest = sqlite3VdbeAddOp1(v, OP_If, regHit); VdbeCoverage(v);
    }
    for(i=0, pC=pAggInfo->aCol; i<pAggInfo->nAccumulator; i++, pC++){
      sqlite3ExprCode(pParse, pC->pCExpr, pC->iMem);
    }
  
    pAggInfo->directMode = 0;
    if( addrHitTest ){
      sqlite3VdbeJumpHereOrPopInst(v, addrHitTest);
    }
  }
  
  /*
  ** Add a single OP_Explain instruction to the VDBE to explain a simple
  ** count(*) query ("SELECT count(*) FROM pTab").
  */
  #ifndef SQLITE_OMIT_EXPLAIN
  static void explainSimpleCount(
    Parse *pParse,                  /* Parse context */
    Table *pTab,                    /* Table being queried */
    Index *pIdx                     /* Index used to optimize scan, or NULL */
  ){
    if( pParse->explain==2 ){
      int bCover = (pIdx!=0 && (HasRowid(pTab) || !IsPrimaryKeyIndex(pIdx)));
      sqlite3VdbeExplain(pParse, 0, "SCAN %s%s%s",
          pTab->zName,
          bCover ? " USING COVERING INDEX " : "",
          bCover ? pIdx->zName : ""
      );
    }
  }
  #else
  # define explainSimpleCount(a,b,c)
  #endif
  
  /*
  ** sqlite3WalkExpr() callback used by havingToWhere().
  **
  ** If the node passed to the callback is a TK_AND node, return 
  ** WRC_Continue to tell sqlite3WalkExpr() to iterate through child nodes.
  **
  ** Otherwise, return WRC_Prune. In this case, also check if the 
  ** sub-expression matches the criteria for being moved to the WHERE
  ** clause. If so, add it to the WHERE clause and replace the sub-expression
  ** within the HAVING expression with a constant "1".
  */
  static int havingToWhereExprCb(Walker *pWalker, Expr *pExpr){
    if( pExpr->op!=TK_AND ){
      Select *pS = pWalker->u.pSelect;
      /* This routine is called before the HAVING clause of the current
      ** SELECT is analyzed for aggregates. So if pExpr->pAggInfo is set
      ** here, it indicates that the expression is a correlated reference to a
      ** column from an outer aggregate query, or an aggregate function that
      ** belongs to an outer query. Do not move the expression to the WHERE
      ** clause in this obscure case, as doing so may corrupt the outer Select
      ** statements AggInfo structure.  */
      if( sqlite3ExprIsConstantOrGroupBy(pWalker->pParse, pExpr, pS->pGroupBy) 
       && ExprAlwaysFalse(pExpr)==0
       && pExpr->pAggInfo==0
      ){
        sqlite3 *db = pWalker->pParse->db;
        Expr *pNew = sqlite3Expr(db, TK_INTEGER, "1");
        if( pNew ){
          Expr *pWhere = pS->pWhere;
          SWAP(Expr, *pNew, *pExpr);
          pNew = sqlite3ExprAnd(pWalker->pParse, pWhere, pNew);
          pS->pWhere = pNew;
          pWalker->eCode = 1;
        }
      }
      return WRC_Prune;
    }
    return WRC_Continue;
  }
  
  /*
  ** Transfer eligible terms from the HAVING clause of a query, which is
  ** processed after grouping, to the WHERE clause, which is processed before
  ** grouping. For example, the query:
  **
  **   SELECT * FROM <tables> WHERE a=? GROUP BY b HAVING b=? AND c=?
  **
  ** can be rewritten as:
  **
  **   SELECT * FROM <tables> WHERE a=? AND b=? GROUP BY b HAVING c=?
  **
  ** A term of the HAVING expression is eligible for transfer if it consists
  ** entirely of constants and expressions that are also GROUP BY terms that
  ** use the "BINARY" collation sequence.
  */
  static void havingToWhere(Parse *pParse, Select *p){
    Walker sWalker;
    memset(&sWalker, 0, sizeof(sWalker));
    sWalker.pParse = pParse;
    sWalker.xExprCallback = havingToWhereExprCb;
    sWalker.u.pSelect = p;
    sqlite3WalkExpr(&sWalker, p->pHaving);
  #if SELECTTRACE_ENABLED
    if( sWalker.eCode && (sqlite3SelectTrace & 0x100)!=0 ){
      SELECTTRACE(0x100,pParse,p,("Move HAVING terms into WHERE:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  }
  
  /*
  ** Check to see if the pThis entry of pTabList is a self-join of a prior view.
  ** If it is, then return the SrcList_item for the prior view.  If it is not,
  ** then return 0.
  */
  static SrcItem *isSelfJoinView(
    SrcList *pTabList,           /* Search for self-joins in this FROM clause */
    SrcItem *pThis               /* Search for prior reference to this subquery */
  ){
    SrcItem *pItem;
    assert( pThis->pSelect!=0 );
    if( pThis->pSelect->selFlags & SF_PushDown ) return 0;
    for(pItem = pTabList->a; pItem<pThis; pItem++){
      Select *pS1;
      if( pItem->pSelect==0 ) continue;
      if( pItem->fg.viaCoroutine ) continue;
      if( pItem->zName==0 ) continue;
      assert( pItem->pTab!=0 );
      assert( pThis->pTab!=0 );
      if( pItem->pTab->pSchema!=pThis->pTab->pSchema ) continue;
      if( sqlite3_stricmp(pItem->zName, pThis->zName)!=0 ) continue;
      pS1 = pItem->pSelect;
      if( pItem->pTab->pSchema==0 && pThis->pSelect->selId!=pS1->selId ){
        /* The query flattener left two different CTE tables with identical
        ** names in the same FROM clause. */
        continue;
      }
      if( pItem->pSelect->selFlags & SF_PushDown ){
        /* The view was modified by some other optimization such as
        ** pushDownWhereTerms() */
        continue;
      }
      return pItem;
    }
    return 0;
  }
  
  /*
  ** Deallocate a single AggInfo object
  */
  static void agginfoFree(sqlite3 *db, AggInfo *p){
    sqlite3DbFree(db, p->aCol);
    sqlite3DbFree(db, p->aFunc);
    sqlite3DbFreeNN(db, p);
  }
  
  #ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
  /*
  ** Attempt to transform a query of the form
  **
  **    SELECT count(*) FROM (SELECT x FROM t1 UNION ALL SELECT y FROM t2)
  **
  ** Into this:
  **
  **    SELECT (SELECT count(*) FROM t1)+(SELECT count(*) FROM t2)
  **
  ** The transformation only works if all of the following are true:
  **
  **   *  The subquery is a UNION ALL of two or more terms
  **   *  The subquery does not have a LIMIT clause
  **   *  There is no WHERE or GROUP BY or HAVING clauses on the subqueries
  **   *  The outer query is a simple count(*) with no WHERE clause or other
  **      extraneous syntax.
  **
  ** Return TRUE if the optimization is undertaken.
  */
  static int countOfViewOptimization(Parse *pParse, Select *p){
    Select *pSub, *pPrior;
    Expr *pExpr;
    Expr *pCount;
    sqlite3 *db;
    if( (p->selFlags & SF_Aggregate)==0 ) return 0;   /* This is an aggregate */
    if( p->pEList->nExpr!=1 ) return 0;               /* Single result column */
    if( p->pWhere ) return 0;
    if( p->pGroupBy ) return 0;
    pExpr = p->pEList->a[0].pExpr;
    if( pExpr->op!=TK_AGG_FUNCTION ) return 0;        /* Result is an aggregate */
    if( sqlite3_stricmp(pExpr->u.zToken,"count") ) return 0;  /* Is count() */
    if( pExpr->x.pList!=0 ) return 0;                 /* Must be count(*) */
    if( p->pSrc->nSrc!=1 ) return 0;                  /* One table in FROM  */
    pSub = p->pSrc->a[0].pSelect;
    if( pSub==0 ) return 0;                           /* The FROM is a subquery */
    if( pSub->pPrior==0 ) return 0;                   /* Must be a compound ry */
    do{
      if( pSub->op!=TK_ALL && pSub->pPrior ) return 0;  /* Must be UNION ALL */
      if( pSub->pWhere ) return 0;                      /* No WHERE clause */
      if( pSub->pLimit ) return 0;                      /* No LIMIT clause */
      if( pSub->selFlags & SF_Aggregate ) return 0;     /* Not an aggregate */
      pSub = pSub->pPrior;                              /* Repeat over compound */
    }while( pSub );
  
    /* If we reach this point then it is OK to perform the transformation */
  
    db = pParse->db;
    pCount = pExpr;
    pExpr = 0;
    pSub = p->pSrc->a[0].pSelect;
    p->pSrc->a[0].pSelect = 0;
    sqlite3SrcListDelete(db, p->pSrc);
    p->pSrc = sqlite3DbMallocZero(pParse->db, sizeof(*p->pSrc));
    while( pSub ){
      Expr *pTerm;
      pPrior = pSub->pPrior;
      pSub->pPrior = 0;
      pSub->pNext = 0;
      pSub->selFlags |= SF_Aggregate;
      pSub->selFlags &= ~SF_Compound;
      pSub->nSelectRow = 0;
      sqlite3ExprListDelete(db, pSub->pEList);
      pTerm = pPrior ? sqlite3ExprDup(db, pCount, 0) : pCount;
      pSub->pEList = sqlite3ExprListAppend(pParse, 0, pTerm);
      pTerm = sqlite3PExpr(pParse, TK_SELECT, 0, 0);
      sqlite3PExprAddSelect(pParse, pTerm, pSub);
      if( pExpr==0 ){
        pExpr = pTerm;
      }else{
        pExpr = sqlite3PExpr(pParse, TK_PLUS, pTerm, pExpr);
      }
      pSub = pPrior;
    }
    p->pEList->a[0].pExpr = pExpr;
    p->selFlags &= ~SF_Aggregate;
  
  #if SELECTTRACE_ENABLED
    if( sqlite3SelectTrace & 0x400 ){
      SELECTTRACE(0x400,pParse,p,("After count-of-view optimization:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
    return 1;
  }
  #endif /* SQLITE_COUNTOFVIEW_OPTIMIZATION */
  
  /*
  ** Generate code for the SELECT statement given in the p argument.  
  **
  ** The results are returned according to the SelectDest structure.
  ** See comments in sqliteInt.h for further information.
  **
  ** This routine returns the number of errors.  If any errors are
  ** encountered, then an appropriate error message is left in
  ** pParse->zErrMsg.
  **
  ** This routine does NOT free the Select structure passed in.  The
  ** calling function needs to do that.
  */
  int sqlite3Select(
    Parse *pParse,         /* The parser context */
    Select *p,             /* The SELECT statement being coded. */
    SelectDest *pDest      /* What to do with the query results */
  ){
    int i, j;              /* Loop counters */
    WhereInfo *pWInfo;     /* Return from sqlite3WhereBegin() */
    Vdbe *v;               /* The virtual machine under construction */
    int isAgg;             /* True for select lists like "count(*)" */
    ExprList *pEList = 0;  /* List of columns to extract. */
    SrcList *pTabList;     /* List of tables to select from */
    Expr *pWhere;          /* The WHERE clause.  May be NULL */
    ExprList *pGroupBy;    /* The GROUP BY clause.  May be NULL */
    Expr *pHaving;         /* The HAVING clause.  May be NULL */
    AggInfo *pAggInfo = 0; /* Aggregate information */
    int rc = 1;            /* Value to return from this function */
    DistinctCtx sDistinct; /* Info on how to code the DISTINCT keyword */
    SortCtx sSort;         /* Info on how to code the ORDER BY clause */
    int iEnd;              /* Address of the end of the query */
    sqlite3 *db;           /* The database connection */
    ExprList *pMinMaxOrderBy = 0;  /* Added ORDER BY for min/max queries */
    u8 minMaxFlag;                 /* Flag for min/max queries */
  
    db = pParse->db;
    v = sqlite3GetVdbe(pParse);
    if( p==0 || db->mallocFailed || pParse->nErr ){
      return 1;
    }
    if( sqlite3AuthCheck(pParse, SQLITE_SELECT, 0, 0, 0) ) return 1;
  #if SELECTTRACE_ENABLED
    SELECTTRACE(1,pParse,p, ("begin processing:\n", pParse->addrExplain));
    if( sqlite3SelectTrace & 0x100 ){
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  
    assert( p->pOrderBy==0 || pDest->eDest!=SRT_DistFifo );
    assert( p->pOrderBy==0 || pDest->eDest!=SRT_Fifo );
    assert( p->pOrderBy==0 || pDest->eDest!=SRT_DistQueue );
    assert( p->pOrderBy==0 || pDest->eDest!=SRT_Queue );
    if( IgnorableDistinct(pDest) ){
      assert(pDest->eDest==SRT_Exists     || pDest->eDest==SRT_Union || 
             pDest->eDest==SRT_Except     || pDest->eDest==SRT_Discard ||
             pDest->eDest==SRT_DistQueue  || pDest->eDest==SRT_DistFifo );
      /* All of these destinations are also able to ignore the ORDER BY clause */
      if( p->pOrderBy ){
  #if SELECTTRACE_ENABLED
        SELECTTRACE(1,pParse,p, ("dropping superfluous ORDER BY:\n"));
        if( sqlite3SelectTrace & 0x100 ){
          sqlite3TreeViewExprList(0, p->pOrderBy, 0, "ORDERBY");
        }
  #endif    
        sqlite3ParserAddCleanup(pParse,
          (void(*)(sqlite3*,void*))sqlite3ExprListDelete,
          p->pOrderBy);
        testcase( pParse->earlyCleanup );
        p->pOrderBy = 0;
      }
      p->selFlags &= ~SF_Distinct;
      p->selFlags |= SF_NoopOrderBy;
    }
    sqlite3SelectPrep(pParse, p, 0);
    if( pParse->nErr || db->mallocFailed ){
      goto select_end;
    }
    assert( p->pEList!=0 );
  #if SELECTTRACE_ENABLED
    if( sqlite3SelectTrace & 0x104 ){
      SELECTTRACE(0x104,pParse,p, ("after name resolution:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  
    /* If the SF_UFSrcCheck flag is set, then this function is being called
    ** as part of populating the temp table for an UPDATE...FROM statement.
    ** In this case, it is an error if the target object (pSrc->a[0]) name 
    ** or alias is duplicated within FROM clause (pSrc->a[1..n]).  
    **
    ** Postgres disallows this case too. The reason is that some other 
    ** systems handle this case differently, and not all the same way, 
    ** which is just confusing. To avoid this, we follow PG's lead and
    ** disallow it altogether.  */
    if( p->selFlags & SF_UFSrcCheck ){
      SrcItem *p0 = &p->pSrc->a[0];
      for(i=1; i<p->pSrc->nSrc; i++){
        SrcItem *p1 = &p->pSrc->a[i];
        if( p0->pTab==p1->pTab && 0==sqlite3_stricmp(p0->zAlias, p1->zAlias) ){
          sqlite3ErrorMsg(pParse, 
              "target object/alias may not appear in FROM clause: %s", 
              p0->zAlias ? p0->zAlias : p0->pTab->zName
          );
          goto select_end;
        }
      }
  
      /* Clear the SF_UFSrcCheck flag. The check has already been performed,
      ** and leaving this flag set can cause errors if a compound sub-query
      ** in p->pSrc is flattened into this query and this function called
      ** again as part of compound SELECT processing.  */
      p->selFlags &= ~SF_UFSrcCheck;
    }
  
    if( pDest->eDest==SRT_Output ){
      sqlite3GenerateColumnNames(pParse, p);
    }
  
  #ifndef SQLITE_OMIT_WINDOWFUNC
    if( sqlite3WindowRewrite(pParse, p) ){
      assert( db->mallocFailed || pParse->nErr>0 );
      goto select_end;
    }
  #if SELECTTRACE_ENABLED
    if( p->pWin && (sqlite3SelectTrace & 0x108)!=0 ){
      SELECTTRACE(0x104,pParse,p, ("after window rewrite:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  #endif /* SQLITE_OMIT_WINDOWFUNC */
    pTabList = p->pSrc;
    isAgg = (p->selFlags & SF_Aggregate)!=0;
    memset(&sSort, 0, sizeof(sSort));
    sSort.pOrderBy = p->pOrderBy;
  
    /* Try to do various optimizations (flattening subqueries, and strength
    ** reduction of join operators) in the FROM clause up into the main query
    */
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
    for(i=0; !p->pPrior && i<pTabList->nSrc; i++){
      SrcItem *pItem = &pTabList->a[i];
      Select *pSub = pItem->pSelect;
      Table *pTab = pItem->pTab;
  
      /* The expander should have already created transient Table objects
      ** even for FROM clause elements such as subqueries that do not correspond
      ** to a real table */
      assert( pTab!=0 );
  
      /* Convert LEFT JOIN into JOIN if there are terms of the right table
      ** of the LEFT JOIN used in the WHERE clause.
      */
      if( (pItem->fg.jointype & JT_LEFT)!=0
       && sqlite3ExprImpliesNonNullRow(p->pWhere, pItem->iCursor)
       && OptimizationEnabled(db, SQLITE_SimplifyJoin)
      ){
        SELECTTRACE(0x100,pParse,p,
                  ("LEFT-JOIN simplifies to JOIN on term %d\n",i));
        pItem->fg.jointype &= ~(JT_LEFT|JT_OUTER);
        unsetJoinExpr(p->pWhere, pItem->iCursor);
      }
  
      /* No futher action if this term of the FROM clause is no a subquery */
      if( pSub==0 ) continue;
  
      /* Catch mismatch in the declared columns of a view and the number of
      ** columns in the SELECT on the RHS */
      if( pTab->nCol!=pSub->pEList->nExpr ){
        sqlite3ErrorMsg(pParse, "expected %d columns for '%s' but got %d",
                        pTab->nCol, pTab->zName, pSub->pEList->nExpr);
        goto select_end;
      }
  
      /* Do not try to flatten an aggregate subquery.
      **
      ** Flattening an aggregate subquery is only possible if the outer query
      ** is not a join.  But if the outer query is not a join, then the subquery
      ** will be implemented as a co-routine and there is no advantage to
      ** flattening in that case.
      */
      if( (pSub->selFlags & SF_Aggregate)!=0 ) continue;
      assert( pSub->pGroupBy==0 );
  
      /* If a FROM-clause subquery has an ORDER BY clause that is not
      ** really doing anything, then delete it now so that it does not
      ** interfere with query flattening.  See the discussion at
      ** https://sqlite.org/forum/forumpost/2d76f2bcf65d256a
      **
      ** Beware of these cases where the ORDER BY clause may not be safely
      ** omitted:
      **
      **    (1)   There is also a LIMIT clause
      **    (2)   The subquery was added to help with window-function
      **          processing
      **    (3)   The subquery is in the FROM clause of an UPDATE
      **    (4)   The outer query uses an aggregate function other than
      **          the built-in count(), min(), or max().
      **    (5)   The ORDER BY isn't going to accomplish anything because
      **          one of:
      **            (a)  The outer query has a different ORDER BY clause
      **            (b)  The subquery is part of a join
      **          See forum post 062d576715d277c8
      */
      if( pSub->pOrderBy!=0
       && (p->pOrderBy!=0 || pTabList->nSrc>1)      /* Condition (5) */
       && pSub->pLimit==0                           /* Condition (1) */
       && (pSub->selFlags & SF_OrderByReqd)==0      /* Condition (2) */
       && (p->selFlags & SF_OrderByReqd)==0         /* Condition (3) and (4) */
       && OptimizationEnabled(db, SQLITE_OmitOrderBy)
      ){
        SELECTTRACE(0x100,pParse,p,
                  ("omit superfluous ORDER BY on %r FROM-clause subquery\n",i+1));
        sqlite3ExprListDelete(db, pSub->pOrderBy);
        pSub->pOrderBy = 0;
      }
  
      /* If the outer query contains a "complex" result set (that is,
      ** if the result set of the outer query uses functions or subqueries)
      ** and if the subquery contains an ORDER BY clause and if
      ** it will be implemented as a co-routine, then do not flatten.  This
      ** restriction allows SQL constructs like this:
      **
      **  SELECT expensive_function(x)
      **    FROM (SELECT x FROM tab ORDER BY y LIMIT 10);
      **
      ** The expensive_function() is only computed on the 10 rows that
      ** are output, rather than every row of the table.
      **
      ** The requirement that the outer query have a complex result set
      ** means that flattening does occur on simpler SQL constraints without
      ** the expensive_function() like:
      **
      **  SELECT x FROM (SELECT x FROM tab ORDER BY y LIMIT 10);
      */
      if( pSub->pOrderBy!=0
       && i==0
       && (p->selFlags & SF_ComplexResult)!=0
       && (pTabList->nSrc==1
           || (pTabList->a[1].fg.jointype&(JT_LEFT|JT_CROSS))!=0)
      ){
        continue;
      }
  
      if( flattenSubquery(pParse, p, i, isAgg) ){
        if( pParse->nErr ) goto select_end;
        /* This subquery can be absorbed into its parent. */
        i = -1;
      }
      pTabList = p->pSrc;
      if( db->mallocFailed ) goto select_end;
      if( !IgnorableOrderby(pDest) ){
        sSort.pOrderBy = p->pOrderBy;
      }
    }
  #endif
  
  #ifndef SQLITE_OMIT_COMPOUND_SELECT
    /* Handle compound SELECT statements using the separate multiSelect()
    ** procedure.
    */
    if( p->pPrior ){
      rc = multiSelect(pParse, p, pDest);
  #if SELECTTRACE_ENABLED
      SELECTTRACE(0x1,pParse,p,("end compound-select processing\n"));
      if( (sqlite3SelectTrace & 0x2000)!=0 && ExplainQueryPlanParent(pParse)==0 ){
        sqlite3TreeViewSelect(0, p, 0);
      }
  #endif
      if( p->pNext==0 ) ExplainQueryPlanPop(pParse);
      return rc;
    }
  #endif
  
    /* Do the WHERE-clause constant propagation optimization if this is
    ** a join.  No need to speed time on this operation for non-join queries
    ** as the equivalent optimization will be handled by query planner in
    ** sqlite3WhereBegin().
    */
    if( p->pWhere!=0
     && p->pWhere->op==TK_AND
     && OptimizationEnabled(db, SQLITE_PropagateConst)
     && propagateConstants(pParse, p)
    ){
  #if SELECTTRACE_ENABLED
      if( sqlite3SelectTrace & 0x100 ){
        SELECTTRACE(0x100,pParse,p,("After constant propagation:\n"));
        sqlite3TreeViewSelect(0, p, 0);
      }
  #endif
    }else{
      SELECTTRACE(0x100,pParse,p,("Constant propagation not helpful\n"));
    }
  
  #ifdef SQLITE_COUNTOFVIEW_OPTIMIZATION
    if( OptimizationEnabled(db, SQLITE_QueryFlattener|SQLITE_CountOfView)
     && countOfViewOptimization(pParse, p)
    ){
      if( db->mallocFailed ) goto select_end;
      pEList = p->pEList;
      pTabList = p->pSrc;
    }
  #endif
  
    /* For each term in the FROM clause, do two things:
    ** (1) Authorized unreferenced tables
    ** (2) Generate code for all sub-queries
    */
    for(i=0; i<pTabList->nSrc; i++){
      SrcItem *pItem = &pTabList->a[i];
      SrcItem *pPrior;
      SelectDest dest;
      Select *pSub;
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
      const char *zSavedAuthContext;
  #endif
  
      /* Issue SQLITE_READ authorizations with a fake column name for any
      ** tables that are referenced but from which no values are extracted.
      ** Examples of where these kinds of null SQLITE_READ authorizations
      ** would occur:
      **
      **     SELECT count(*) FROM t1;   -- SQLITE_READ t1.""
      **     SELECT t1.* FROM t1, t2;   -- SQLITE_READ t2.""
      **
      ** The fake column name is an empty string.  It is possible for a table to
      ** have a column named by the empty string, in which case there is no way to
      ** distinguish between an unreferenced table and an actual reference to the
      ** "" column. The original design was for the fake column name to be a NULL,
      ** which would be unambiguous.  But legacy authorization callbacks might
      ** assume the column name is non-NULL and segfault.  The use of an empty
      ** string for the fake column name seems safer.
      */
      if( pItem->colUsed==0 && pItem->zName!=0 ){
        sqlite3AuthCheck(pParse, SQLITE_READ, pItem->zName, "", pItem->zDatabase);
      }
  
  #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)
      /* Generate code for all sub-queries in the FROM clause
      */
      pSub = pItem->pSelect;
      if( pSub==0 ) continue;
  
      /* The code for a subquery should only be generated once. */
      assert( pItem->addrFillSub==0 );
  
      /* Increment Parse.nHeight by the height of the largest expression
      ** tree referred to by this, the parent select. The child select
      ** may contain expression trees of at most
      ** (SQLITE_MAX_EXPR_DEPTH-Parse.nHeight) height. This is a bit
      ** more conservative than necessary, but much easier than enforcing
      ** an exact limit.
      */
      pParse->nHeight += sqlite3SelectExprHeight(p);
  
      /* Make copies of constant WHERE-clause terms in the outer query down
      ** inside the subquery.  This can help the subquery to run more efficiently.
      */
      if( OptimizationEnabled(db, SQLITE_PushDown)
       && (pItem->fg.isCte==0 || pItem->u2.pCteUse->eM10d!=M10d_Yes)
       && pushDownWhereTerms(pParse, pSub, p->pWhere, pItem->iCursor,
                             (pItem->fg.jointype & JT_OUTER)!=0)
      ){
  #if SELECTTRACE_ENABLED
        if( sqlite3SelectTrace & 0x100 ){
          SELECTTRACE(0x100,pParse,p,
              ("After WHERE-clause push-down into subquery %d:\n", pSub->selId));
          sqlite3TreeViewSelect(0, p, 0);
        }
  #endif
        assert( pItem->pSelect && (pItem->pSelect->selFlags & SF_PushDown)!=0 );
      }else{
        SELECTTRACE(0x100,pParse,p,("Push-down not possible\n"));
      }
  
      zSavedAuthContext = pParse->zAuthContext;
      pParse->zAuthContext = pItem->zName;
  
      /* Generate code to implement the subquery
      **
      ** The subquery is implemented as a co-routine if:
      **    (1)  the subquery is guaranteed to be the outer loop (so that
      **         it does not need to be computed more than once), and
      **    (2)  the subquery is not a CTE that should be materialized
      **
      ** TODO: Are there other reasons beside (1) and (2) to use a co-routine
      ** implementation?
      */
      if( i==0
       && (pTabList->nSrc==1
              || (pTabList->a[1].fg.jointype&(JT_LEFT|JT_CROSS))!=0)  /* (1) */
       && (pItem->fg.isCte==0 || pItem->u2.pCteUse->eM10d!=M10d_Yes)  /* (2) */
      ){
        /* Implement a co-routine that will return a single row of the result
        ** set on each invocation.
        */
        int addrTop = sqlite3VdbeCurrentAddr(v)+1;
       
        pItem->regReturn = ++pParse->nMem;
        sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
        VdbeComment((v, "%!S", pItem));
        pItem->addrFillSub = addrTop;
        sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
        ExplainQueryPlan((pParse, 1, "CO-ROUTINE %!S", pItem));
        sqlite3Select(pParse, pSub, &dest);
        pItem->pTab->nRowLogEst = pSub->nSelectRow;
        pItem->fg.viaCoroutine = 1;
        pItem->regResult = dest.iSdst;
        sqlite3VdbeEndCoroutine(v, pItem->regReturn);
        sqlite3VdbeJumpHere(v, addrTop-1);
        sqlite3ClearTempRegCache(pParse);
      }else if( pItem->fg.isCte && pItem->u2.pCteUse->addrM9e>0 ){
        /* This is a CTE for which materialization code has already been
        ** generated.  Invoke the subroutine to compute the materialization,
        ** the make the pItem->iCursor be a copy of the ephemerial table that
        ** holds the result of the materialization. */
        CteUse *pCteUse = pItem->u2.pCteUse;
        sqlite3VdbeAddOp2(v, OP_Gosub, pCteUse->regRtn, pCteUse->addrM9e);
        if( pItem->iCursor!=pCteUse->iCur ){
          sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pCteUse->iCur);
        }
        pSub->nSelectRow = pCteUse->nRowEst;
      }else if( (pPrior = isSelfJoinView(pTabList, pItem))!=0 ){
        /* This view has already been materialized by a prior entry in
        ** this same FROM clause.  Reuse it. */
        if( pPrior->addrFillSub ){
          sqlite3VdbeAddOp2(v, OP_Gosub, pPrior->regReturn, pPrior->addrFillSub);
        }
        sqlite3VdbeAddOp2(v, OP_OpenDup, pItem->iCursor, pPrior->iCursor);
        pSub->nSelectRow = pPrior->pSelect->nSelectRow;
      }else{
        /* Materialize the view.  If the view is not correlated, generate a
        ** subroutine to do the materialization so that subsequent uses of
        ** the same view can reuse the materialization. */
        int topAddr;
        int onceAddr = 0;
        int retAddr;
  
        pItem->regReturn = ++pParse->nMem;
        topAddr = sqlite3VdbeAddOp2(v, OP_Integer, 0, pItem->regReturn);
        pItem->addrFillSub = topAddr+1;
        if( pItem->fg.isCorrelated==0 ){
          /* If the subquery is not correlated and if we are not inside of
          ** a trigger, then we only need to compute the value of the subquery
          ** once. */
          onceAddr = sqlite3VdbeAddOp0(v, OP_Once); VdbeCoverage(v);
          VdbeComment((v, "materialize %!S", pItem));
        }else{
          VdbeNoopComment((v, "materialize %!S", pItem));
        }
        sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
        ExplainQueryPlan((pParse, 1, "MATERIALIZE %!S", pItem));
        sqlite3Select(pParse, pSub, &dest);
        pItem->pTab->nRowLogEst = pSub->nSelectRow;
        if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
        retAddr = sqlite3VdbeAddOp1(v, OP_Return, pItem->regReturn);
        VdbeComment((v, "end %!S", pItem));
        sqlite3VdbeChangeP1(v, topAddr, retAddr);
        sqlite3ClearTempRegCache(pParse);
        if( pItem->fg.isCte && pItem->fg.isCorrelated==0 ){
          CteUse *pCteUse = pItem->u2.pCteUse;
          pCteUse->addrM9e = pItem->addrFillSub;
          pCteUse->regRtn = pItem->regReturn;
          pCteUse->iCur = pItem->iCursor;
          pCteUse->nRowEst = pSub->nSelectRow;
        }
      }
      if( db->mallocFailed ) goto select_end;
      pParse->nHeight -= sqlite3SelectExprHeight(p);
      pParse->zAuthContext = zSavedAuthContext;
  #endif
    }
  
    /* Various elements of the SELECT copied into local variables for
    ** convenience */
    pEList = p->pEList;
    pWhere = p->pWhere;
    pGroupBy = p->pGroupBy;
    pHaving = p->pHaving;
    sDistinct.isTnct = (p->selFlags & SF_Distinct)!=0;
  
  #if SELECTTRACE_ENABLED
    if( sqlite3SelectTrace & 0x400 ){
      SELECTTRACE(0x400,pParse,p,("After all FROM-clause analysis:\n"));
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
  
    /* If the query is DISTINCT with an ORDER BY but is not an aggregate, and 
    ** if the select-list is the same as the ORDER BY list, then this query
    ** can be rewritten as a GROUP BY. In other words, this:
    **
    **     SELECT DISTINCT xyz FROM ... ORDER BY xyz
    **
    ** is transformed to:
    **
    **     SELECT xyz FROM ... GROUP BY xyz ORDER BY xyz
    **
    ** The second form is preferred as a single index (or temp-table) may be 
    ** used for both the ORDER BY and DISTINCT processing. As originally 
    ** written the query must use a temp-table for at least one of the ORDER 
    ** BY and DISTINCT, and an index or separate temp-table for the other.
    */
    if( (p->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct 
     && sqlite3ExprListCompare(sSort.pOrderBy, pEList, -1)==0
  #ifndef SQLITE_OMIT_WINDOWFUNC
     && p->pWin==0
  #endif
    ){
      p->selFlags &= ~SF_Distinct;
      pGroupBy = p->pGroupBy = sqlite3ExprListDup(db, pEList, 0);
      p->selFlags |= SF_Aggregate;
      /* Notice that even thought SF_Distinct has been cleared from p->selFlags,
      ** the sDistinct.isTnct is still set.  Hence, isTnct represents the
      ** original setting of the SF_Distinct flag, not the current setting */
      assert( sDistinct.isTnct );
  
  #if SELECTTRACE_ENABLED
      if( sqlite3SelectTrace & 0x400 ){
        SELECTTRACE(0x400,pParse,p,("Transform DISTINCT into GROUP BY:\n"));
        sqlite3TreeViewSelect(0, p, 0);
      }
  #endif
    }
  
    /* If there is an ORDER BY clause, then create an ephemeral index to
    ** do the sorting.  But this sorting ephemeral index might end up
    ** being unused if the data can be extracted in pre-sorted order.
    ** If that is the case, then the OP_OpenEphemeral instruction will be
    ** changed to an OP_Noop once we figure out that the sorting index is
    ** not needed.  The sSort.addrSortIndex variable is used to facilitate
    ** that change.
    */
    if( sSort.pOrderBy ){
      KeyInfo *pKeyInfo;
      pKeyInfo = sqlite3KeyInfoFromExprList(
          pParse, sSort.pOrderBy, 0, pEList->nExpr);
      sSort.iECursor = pParse->nTab++;
      sSort.addrSortIndex =
        sqlite3VdbeAddOp4(v, OP_OpenEphemeral,
            sSort.iECursor, sSort.pOrderBy->nExpr+1+pEList->nExpr, 0,
            (char*)pKeyInfo, P4_KEYINFO
        );
    }else{
      sSort.addrSortIndex = -1;
    }
  
    /* If the output is destined for a temporary table, open that table.
    */
    if( pDest->eDest==SRT_EphemTab ){
      sqlite3VdbeAddOp2(v, OP_OpenEphemeral, pDest->iSDParm, pEList->nExpr);
    }
  
    /* Set the limiter.
    */
    iEnd = sqlite3VdbeMakeLabel(pParse);
    if( (p->selFlags & SF_FixedLimit)==0 ){
      p->nSelectRow = 320;  /* 4 billion rows */
    }
    computeLimitRegisters(pParse, p, iEnd);
    if( p->iLimit==0 && sSort.addrSortIndex>=0 ){
      sqlite3VdbeChangeOpcode(v, sSort.addrSortIndex, OP_SorterOpen);
      sSort.sortFlags |= SORTFLAG_UseSorter;
    }
  
    /* Open an ephemeral index to use for the distinct set.
    */
    if( p->selFlags & SF_Distinct ){
      sDistinct.tabTnct = pParse->nTab++;
      sDistinct.addrTnct = sqlite3VdbeAddOp4(v, OP_OpenEphemeral,
                         sDistinct.tabTnct, 0, 0,
                         (char*)sqlite3KeyInfoFromExprList(pParse, p->pEList,0,0),
                         P4_KEYINFO);
      sqlite3VdbeChangeP5(v, BTREE_UNORDERED);
      sDistinct.eTnctType = WHERE_DISTINCT_UNORDERED;
    }else{
      sDistinct.eTnctType = WHERE_DISTINCT_NOOP;
    }
  
    if( !isAgg && pGroupBy==0 ){
      /* No aggregate functions and no GROUP BY clause */
      u16 wctrlFlags = (sDistinct.isTnct ? WHERE_WANT_DISTINCT : 0)
                     | (p->selFlags & SF_FixedLimit);
  #ifndef SQLITE_OMIT_WINDOWFUNC
      Window *pWin = p->pWin;      /* Main window object (or NULL) */
      if( pWin ){
        sqlite3WindowCodeInit(pParse, p);
      }
  #endif
      assert( WHERE_USE_LIMIT==SF_FixedLimit );
  
  
      /* Begin the database scan. */
      SELECTTRACE(1,pParse,p,("WhereBegin\n"));
      pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, sSort.pOrderBy,
                                 p->pEList, wctrlFlags, p->nSelectRow);
      if( pWInfo==0 ) goto select_end;
      if( sqlite3WhereOutputRowCount(pWInfo) < p->nSelectRow ){
        p->nSelectRow = sqlite3WhereOutputRowCount(pWInfo);
      }
      if( sDistinct.isTnct && sqlite3WhereIsDistinct(pWInfo) ){
        sDistinct.eTnctType = sqlite3WhereIsDistinct(pWInfo);
      }
      if( sSort.pOrderBy ){
        sSort.nOBSat = sqlite3WhereIsOrdered(pWInfo);
        sSort.labelOBLopt = sqlite3WhereOrderByLimitOptLabel(pWInfo);
        if( sSort.nOBSat==sSort.pOrderBy->nExpr ){
          sSort.pOrderBy = 0;
        }
      }
      SELECTTRACE(1,pParse,p,("WhereBegin returns\n"));
  
      /* If sorting index that was created by a prior OP_OpenEphemeral 
      ** instruction ended up not being needed, then change the OP_OpenEphemeral
      ** into an OP_Noop.
      */
      if( sSort.addrSortIndex>=0 && sSort.pOrderBy==0 ){
        sqlite3VdbeChangeToNoop(v, sSort.addrSortIndex);
      }
  
      assert( p->pEList==pEList );
  #ifndef SQLITE_OMIT_WINDOWFUNC
      if( pWin ){
        int addrGosub = sqlite3VdbeMakeLabel(pParse);
        int iCont = sqlite3VdbeMakeLabel(pParse);
        int iBreak = sqlite3VdbeMakeLabel(pParse);
        int regGosub = ++pParse->nMem;
  
        sqlite3WindowCodeStep(pParse, p, pWInfo, regGosub, addrGosub);
  
        sqlite3VdbeAddOp2(v, OP_Goto, 0, iBreak);
        sqlite3VdbeResolveLabel(v, addrGosub);
        VdbeNoopComment((v, "inner-loop subroutine"));
        sSort.labelOBLopt = 0;
        selectInnerLoop(pParse, p, -1, &sSort, &sDistinct, pDest, iCont, iBreak);
        sqlite3VdbeResolveLabel(v, iCont);
        sqlite3VdbeAddOp1(v, OP_Return, regGosub);
        VdbeComment((v, "end inner-loop subroutine"));
        sqlite3VdbeResolveLabel(v, iBreak);
      }else
  #endif /* SQLITE_OMIT_WINDOWFUNC */
      {
        /* Use the standard inner loop. */
        selectInnerLoop(pParse, p, -1, &sSort, &sDistinct, pDest,
            sqlite3WhereContinueLabel(pWInfo),
            sqlite3WhereBreakLabel(pWInfo));
  
        /* End the database scan loop.
        */
        SELECTTRACE(1,pParse,p,("WhereEnd\n"));
        sqlite3WhereEnd(pWInfo);
      }
    }else{
      /* This case when there exist aggregate functions or a GROUP BY clause
      ** or both */
      NameContext sNC;    /* Name context for processing aggregate information */
      int iAMem;          /* First Mem address for storing current GROUP BY */
      int iBMem;          /* First Mem address for previous GROUP BY */
      int iUseFlag;       /* Mem address holding flag indicating that at least
                          ** one row of the input to the aggregator has been
                          ** processed */
      int iAbortFlag;     /* Mem address which causes query abort if positive */
      int groupBySort;    /* Rows come from source in GROUP BY order */
      int addrEnd;        /* End of processing for this SELECT */
      int sortPTab = 0;   /* Pseudotable used to decode sorting results */
      int sortOut = 0;    /* Output register from the sorter */
      int orderByGrp = 0; /* True if the GROUP BY and ORDER BY are the same */
  
      /* Remove any and all aliases between the result set and the
      ** GROUP BY clause.
      */
      if( pGroupBy ){
        int k;                        /* Loop counter */
        struct ExprList_item *pItem;  /* For looping over expression in a list */
  
        for(k=p->pEList->nExpr, pItem=p->pEList->a; k>0; k--, pItem++){
          pItem->u.x.iAlias = 0;
        }
        for(k=pGroupBy->nExpr, pItem=pGroupBy->a; k>0; k--, pItem++){
          pItem->u.x.iAlias = 0;
        }
        assert( 66==sqlite3LogEst(100) );
        if( p->nSelectRow>66 ) p->nSelectRow = 66;
  
        /* If there is both a GROUP BY and an ORDER BY clause and they are
        ** identical, then it may be possible to disable the ORDER BY clause 
        ** on the grounds that the GROUP BY will cause elements to come out 
        ** in the correct order. It also may not - the GROUP BY might use a
        ** database index that causes rows to be grouped together as required
        ** but not actually sorted. Either way, record the fact that the
        ** ORDER BY and GROUP BY clauses are the same by setting the orderByGrp
        ** variable.  */
        if( sSort.pOrderBy && pGroupBy->nExpr==sSort.pOrderBy->nExpr ){
          int ii;
          /* The GROUP BY processing doesn't care whether rows are delivered in
          ** ASC or DESC order - only that each group is returned contiguously.
          ** So set the ASC/DESC flags in the GROUP BY to match those in the 
          ** ORDER BY to maximize the chances of rows being delivered in an 
          ** order that makes the ORDER BY redundant.  */
          for(ii=0; ii<pGroupBy->nExpr; ii++){
            u8 sortFlags = sSort.pOrderBy->a[ii].sortFlags & KEYINFO_ORDER_DESC;
            pGroupBy->a[ii].sortFlags = sortFlags;
          }
          if( sqlite3ExprListCompare(pGroupBy, sSort.pOrderBy, -1)==0 ){
            orderByGrp = 1;
          }
        }
      }else{
        assert( 0==sqlite3LogEst(1) );
        p->nSelectRow = 0;
      }
  
      /* Create a label to jump to when we want to abort the query */
      addrEnd = sqlite3VdbeMakeLabel(pParse);
  
      /* Convert TK_COLUMN nodes into TK_AGG_COLUMN and make entries in
      ** sAggInfo for all TK_AGG_FUNCTION nodes in expressions of the
      ** SELECT statement.
      */
      pAggInfo = sqlite3DbMallocZero(db, sizeof(*pAggInfo) );
      if( pAggInfo ){
        sqlite3ParserAddCleanup(pParse,
            (void(*)(sqlite3*,void*))agginfoFree, pAggInfo);
        testcase( pParse->earlyCleanup );
      }
      if( db->mallocFailed ){
        goto select_end;
      }
      pAggInfo->selId = p->selId;
      memset(&sNC, 0, sizeof(sNC));
      sNC.pParse = pParse;
      sNC.pSrcList = pTabList;
      sNC.uNC.pAggInfo = pAggInfo;
      VVA_ONLY( sNC.ncFlags = NC_UAggInfo; )
      pAggInfo->mnReg = pParse->nMem+1;
      pAggInfo->nSortingColumn = pGroupBy ? pGroupBy->nExpr : 0;
      pAggInfo->pGroupBy = pGroupBy;
      sqlite3ExprAnalyzeAggList(&sNC, pEList);
      sqlite3ExprAnalyzeAggList(&sNC, sSort.pOrderBy);
      if( pHaving ){
        if( pGroupBy ){
          assert( pWhere==p->pWhere );
          assert( pHaving==p->pHaving );
          assert( pGroupBy==p->pGroupBy );
          havingToWhere(pParse, p);
          pWhere = p->pWhere;
        }
        sqlite3ExprAnalyzeAggregates(&sNC, pHaving);
      }
      pAggInfo->nAccumulator = pAggInfo->nColumn;
      if( p->pGroupBy==0 && p->pHaving==0 && pAggInfo->nFunc==1 ){
        minMaxFlag = minMaxQuery(db, pAggInfo->aFunc[0].pFExpr, &pMinMaxOrderBy);
      }else{
        minMaxFlag = WHERE_ORDERBY_NORMAL;
      }
      for(i=0; i<pAggInfo->nFunc; i++){
        Expr *pExpr = pAggInfo->aFunc[i].pFExpr;
        assert( !ExprHasProperty(pExpr, EP_xIsSelect) );
        sNC.ncFlags |= NC_InAggFunc;
        sqlite3ExprAnalyzeAggList(&sNC, pExpr->x.pList);
  #ifndef SQLITE_OMIT_WINDOWFUNC
        assert( !IsWindowFunc(pExpr) );
        if( ExprHasProperty(pExpr, EP_WinFunc) ){
          sqlite3ExprAnalyzeAggregates(&sNC, pExpr->y.pWin->pFilter);
        }
  #endif
        sNC.ncFlags &= ~NC_InAggFunc;
      }
      pAggInfo->mxReg = pParse->nMem;
      if( db->mallocFailed ) goto select_end;
  #if SELECTTRACE_ENABLED
      if( sqlite3SelectTrace & 0x400 ){
        int ii;
        SELECTTRACE(0x400,pParse,p,("After aggregate analysis %p:\n", pAggInfo));
        sqlite3TreeViewSelect(0, p, 0);
        if( minMaxFlag ){
          sqlite3DebugPrintf("MIN/MAX Optimization (0x%02x) adds:\n", minMaxFlag);
          sqlite3TreeViewExprList(0, pMinMaxOrderBy, 0, "ORDERBY");
        }
        for(ii=0; ii<pAggInfo->nColumn; ii++){
          sqlite3DebugPrintf("agg-column[%d] iMem=%d\n",
              ii, pAggInfo->aCol[ii].iMem);
          sqlite3TreeViewExpr(0, pAggInfo->aCol[ii].pCExpr, 0);
        }
        for(ii=0; ii<pAggInfo->nFunc; ii++){
          sqlite3DebugPrintf("agg-func[%d]: iMem=%d\n",
              ii, pAggInfo->aFunc[ii].iMem);
          sqlite3TreeViewExpr(0, pAggInfo->aFunc[ii].pFExpr, 0);
        }
      }
  #endif
  
  
      /* Processing for aggregates with GROUP BY is very different and
      ** much more complex than aggregates without a GROUP BY.
      */
      if( pGroupBy ){
        KeyInfo *pKeyInfo;  /* Keying information for the group by clause */
        int addr1;          /* A-vs-B comparision jump */
        int addrOutputRow;  /* Start of subroutine that outputs a result row */
        int regOutputRow;   /* Return address register for output subroutine */
        int addrSetAbort;   /* Set the abort flag and return */
        int addrTopOfLoop;  /* Top of the input loop */
        int addrSortingIdx; /* The OP_OpenEphemeral for the sorting index */
        int addrReset;      /* Subroutine for resetting the accumulator */
        int regReset;       /* Return address register for reset subroutine */
        ExprList *pDistinct = 0;
        u16 distFlag = 0;
        int eDist = WHERE_DISTINCT_NOOP;
  
        if( pAggInfo->nFunc==1 
         && pAggInfo->aFunc[0].iDistinct>=0
         && pAggInfo->aFunc[0].pFExpr->x.pList
        ){
          Expr *pExpr = pAggInfo->aFunc[0].pFExpr->x.pList->a[0].pExpr;
          pExpr = sqlite3ExprDup(db, pExpr, 0);
          pDistinct = sqlite3ExprListDup(db, pGroupBy, 0);
          pDistinct = sqlite3ExprListAppend(pParse, pDistinct, pExpr);
          distFlag = pDistinct ? (WHERE_WANT_DISTINCT|WHERE_AGG_DISTINCT) : 0;
        }
  
        /* If there is a GROUP BY clause we might need a sorting index to
        ** implement it.  Allocate that sorting index now.  If it turns out
        ** that we do not need it after all, the OP_SorterOpen instruction
        ** will be converted into a Noop.  
        */
        pAggInfo->sortingIdx = pParse->nTab++;
        pKeyInfo = sqlite3KeyInfoFromExprList(pParse, pGroupBy,
                                              0, pAggInfo->nColumn);
        addrSortingIdx = sqlite3VdbeAddOp4(v, OP_SorterOpen, 
            pAggInfo->sortingIdx, pAggInfo->nSortingColumn, 
            0, (char*)pKeyInfo, P4_KEYINFO);
  
        /* Initialize memory locations used by GROUP BY aggregate processing
        */
        iUseFlag = ++pParse->nMem;
        iAbortFlag = ++pParse->nMem;
        regOutputRow = ++pParse->nMem;
        addrOutputRow = sqlite3VdbeMakeLabel(pParse);
        regReset = ++pParse->nMem;
        addrReset = sqlite3VdbeMakeLabel(pParse);
        iAMem = pParse->nMem + 1;
        pParse->nMem += pGroupBy->nExpr;
        iBMem = pParse->nMem + 1;
        pParse->nMem += pGroupBy->nExpr;
        sqlite3VdbeAddOp2(v, OP_Integer, 0, iAbortFlag);
        VdbeComment((v, "clear abort flag"));
        sqlite3VdbeAddOp3(v, OP_Null, 0, iAMem, iAMem+pGroupBy->nExpr-1);
  
        /* Begin a loop that will extract all source rows in GROUP BY order.
        ** This might involve two separate loops with an OP_Sort in between, or
        ** it might be a single loop that uses an index to extract information
        ** in the right order to begin with.
        */
        sqlite3VdbeAddOp2(v, OP_Gosub, regReset, addrReset);
        SELECTTRACE(1,pParse,p,("WhereBegin\n"));
        pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, pGroupBy, pDistinct,
            WHERE_GROUPBY | (orderByGrp ? WHERE_SORTBYGROUP : 0) | distFlag, 0
        );
        if( pWInfo==0 ){
          sqlite3ExprListDelete(db, pDistinct);
          goto select_end;
        }
        eDist = sqlite3WhereIsDistinct(pWInfo);
        SELECTTRACE(1,pParse,p,("WhereBegin returns\n"));
        if( sqlite3WhereIsOrdered(pWInfo)==pGroupBy->nExpr ){
          /* The optimizer is able to deliver rows in group by order so
          ** we do not have to sort.  The OP_OpenEphemeral table will be
          ** cancelled later because we still need to use the pKeyInfo
          */
          groupBySort = 0;
        }else{
          /* Rows are coming out in undetermined order.  We have to push
          ** each row into a sorting index, terminate the first loop,
          ** then loop over the sorting index in order to get the output
          ** in sorted order
          */
          int regBase;
          int regRecord;
          int nCol;
          int nGroupBy;
  
          explainTempTable(pParse, 
              (sDistinct.isTnct && (p->selFlags&SF_Distinct)==0) ?
                      "DISTINCT" : "GROUP BY");
  
          groupBySort = 1;
          nGroupBy = pGroupBy->nExpr;
          nCol = nGroupBy;
          j = nGroupBy;
          for(i=0; i<pAggInfo->nColumn; i++){
            if( pAggInfo->aCol[i].iSorterColumn>=j ){
              nCol++;
              j++;
            }
          }
          regBase = sqlite3GetTempRange(pParse, nCol);
          sqlite3ExprCodeExprList(pParse, pGroupBy, regBase, 0, 0);
          j = nGroupBy;
          for(i=0; i<pAggInfo->nColumn; i++){
            struct AggInfo_col *pCol = &pAggInfo->aCol[i];
            if( pCol->iSorterColumn>=j ){
              int r1 = j + regBase;
              sqlite3ExprCodeGetColumnOfTable(v,
                                 pCol->pTab, pCol->iTable, pCol->iColumn, r1);
              j++;
            }
          }
          regRecord = sqlite3GetTempReg(pParse);
          sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase, nCol, regRecord);
          sqlite3VdbeAddOp2(v, OP_SorterInsert, pAggInfo->sortingIdx, regRecord);
          sqlite3ReleaseTempReg(pParse, regRecord);
          sqlite3ReleaseTempRange(pParse, regBase, nCol);
          SELECTTRACE(1,pParse,p,("WhereEnd\n"));
          sqlite3WhereEnd(pWInfo);
          pAggInfo->sortingIdxPTab = sortPTab = pParse->nTab++;
          sortOut = sqlite3GetTempReg(pParse);
          sqlite3VdbeAddOp3(v, OP_OpenPseudo, sortPTab, sortOut, nCol);
          sqlite3VdbeAddOp2(v, OP_SorterSort, pAggInfo->sortingIdx, addrEnd);
          VdbeComment((v, "GROUP BY sort")); VdbeCoverage(v);
          pAggInfo->useSortingIdx = 1;
        }
  
        /* If the index or temporary table used by the GROUP BY sort
        ** will naturally deliver rows in the order required by the ORDER BY
        ** clause, cancel the ephemeral table open coded earlier.
        **
        ** This is an optimization - the correct answer should result regardless.
        ** Use the SQLITE_GroupByOrder flag with SQLITE_TESTCTRL_OPTIMIZER to 
        ** disable this optimization for testing purposes.  */
        if( orderByGrp && OptimizationEnabled(db, SQLITE_GroupByOrder) 
         && (groupBySort || sqlite3WhereIsSorted(pWInfo))
        ){
          sSort.pOrderBy = 0;
          sqlite3VdbeChangeToNoop(v, sSort.addrSortIndex);
        }
  
        /* Evaluate the current GROUP BY terms and store in b0, b1, b2...
        ** (b0 is memory location iBMem+0, b1 is iBMem+1, and so forth)
        ** Then compare the current GROUP BY terms against the GROUP BY terms
        ** from the previous row currently stored in a0, a1, a2...
        */
        addrTopOfLoop = sqlite3VdbeCurrentAddr(v);
        if( groupBySort ){
          sqlite3VdbeAddOp3(v, OP_SorterData, pAggInfo->sortingIdx,
                            sortOut, sortPTab);
        }
        for(j=0; j<pGroupBy->nExpr; j++){
          if( groupBySort ){
            sqlite3VdbeAddOp3(v, OP_Column, sortPTab, j, iBMem+j);
          }else{
            pAggInfo->directMode = 1;
            sqlite3ExprCode(pParse, pGroupBy->a[j].pExpr, iBMem+j);
          }
        }
        sqlite3VdbeAddOp4(v, OP_Compare, iAMem, iBMem, pGroupBy->nExpr,
                            (char*)sqlite3KeyInfoRef(pKeyInfo), P4_KEYINFO);
        addr1 = sqlite3VdbeCurrentAddr(v);
        sqlite3VdbeAddOp3(v, OP_Jump, addr1+1, 0, addr1+1); VdbeCoverage(v);
  
        /* Generate code that runs whenever the GROUP BY changes.
        ** Changes in the GROUP BY are detected by the previous code
        ** block.  If there were no changes, this block is skipped.
        **
        ** This code copies current group by terms in b0,b1,b2,...
        ** over to a0,a1,a2.  It then calls the output subroutine
        ** and resets the aggregate accumulator registers in preparation
        ** for the next GROUP BY batch.
        */
        sqlite3ExprCodeMove(pParse, iBMem, iAMem, pGroupBy->nExpr);
        sqlite3VdbeAddOp2(v, OP_Gosub, regOutputRow, addrOutputRow);
        VdbeComment((v, "output one row"));
        sqlite3VdbeAddOp2(v, OP_IfPos, iAbortFlag, addrEnd); VdbeCoverage(v);
        VdbeComment((v, "check abort flag"));
        sqlite3VdbeAddOp2(v, OP_Gosub, regReset, addrReset);
        VdbeComment((v, "reset accumulator"));
  
        /* Update the aggregate accumulators based on the content of
        ** the current row
        */
        sqlite3VdbeJumpHere(v, addr1);
        updateAccumulator(pParse, iUseFlag, pAggInfo, eDist);
        sqlite3VdbeAddOp2(v, OP_Integer, 1, iUseFlag);
        VdbeComment((v, "indicate data in accumulator"));
  
        /* End of the loop
        */
        if( groupBySort ){
          sqlite3VdbeAddOp2(v, OP_SorterNext, pAggInfo->sortingIdx,addrTopOfLoop);
          VdbeCoverage(v);
        }else{
          SELECTTRACE(1,pParse,p,("WhereEnd\n"));
          sqlite3WhereEnd(pWInfo);
          sqlite3VdbeChangeToNoop(v, addrSortingIdx);
        }
        sqlite3ExprListDelete(db, pDistinct);
  
        /* Output the final row of result
        */
        sqlite3VdbeAddOp2(v, OP_Gosub, regOutputRow, addrOutputRow);
        VdbeComment((v, "output final row"));
  
        /* Jump over the subroutines
        */
        sqlite3VdbeGoto(v, addrEnd);
  
        /* Generate a subroutine that outputs a single row of the result
        ** set.  This subroutine first looks at the iUseFlag.  If iUseFlag
        ** is less than or equal to zero, the subroutine is a no-op.  If
        ** the processing calls for the query to abort, this subroutine
        ** increments the iAbortFlag memory location before returning in
        ** order to signal the caller to abort.
        */
        addrSetAbort = sqlite3VdbeCurrentAddr(v);
        sqlite3VdbeAddOp2(v, OP_Integer, 1, iAbortFlag);
        VdbeComment((v, "set abort flag"));
        sqlite3VdbeAddOp1(v, OP_Return, regOutputRow);
        sqlite3VdbeResolveLabel(v, addrOutputRow);
        addrOutputRow = sqlite3VdbeCurrentAddr(v);
        sqlite3VdbeAddOp2(v, OP_IfPos, iUseFlag, addrOutputRow+2);
        VdbeCoverage(v);
        VdbeComment((v, "Groupby result generator entry point"));
        sqlite3VdbeAddOp1(v, OP_Return, regOutputRow);
        finalizeAggFunctions(pParse, pAggInfo);
        sqlite3ExprIfFalse(pParse, pHaving, addrOutputRow+1, SQLITE_JUMPIFNULL);
        selectInnerLoop(pParse, p, -1, &sSort,
                        &sDistinct, pDest,
                        addrOutputRow+1, addrSetAbort);
        sqlite3VdbeAddOp1(v, OP_Return, regOutputRow);
        VdbeComment((v, "end groupby result generator"));
  
        /* Generate a subroutine that will reset the group-by accumulator
        */
        sqlite3VdbeResolveLabel(v, addrReset);
        resetAccumulator(pParse, pAggInfo);
        sqlite3VdbeAddOp2(v, OP_Integer, 0, iUseFlag);
        VdbeComment((v, "indicate accumulator empty"));
        sqlite3VdbeAddOp1(v, OP_Return, regReset);
  
        if( eDist!=WHERE_DISTINCT_NOOP ){
          struct AggInfo_func *pF = &pAggInfo->aFunc[0];
          fixDistinctOpenEph(pParse, eDist, pF->iDistinct, pF->iDistAddr);
        }
      } /* endif pGroupBy.  Begin aggregate queries without GROUP BY: */
      else {
        Table *pTab;
        if( (pTab = isSimpleCount(p, pAggInfo))!=0 ){
          /* If isSimpleCount() returns a pointer to a Table structure, then
          ** the SQL statement is of the form:
          **
          **   SELECT count(*) FROM <tbl>
          **
          ** where the Table structure returned represents table <tbl>.
          **
          ** This statement is so common that it is optimized specially. The
          ** OP_Count instruction is executed either on the intkey table that
          ** contains the data for table <tbl> or on one of its indexes. It
          ** is better to execute the op on an index, as indexes are almost
          ** always spread across less pages than their corresponding tables.
          */
          const int iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
          const int iCsr = pParse->nTab++;     /* Cursor to scan b-tree */
          Index *pIdx;                         /* Iterator variable */
          KeyInfo *pKeyInfo = 0;               /* Keyinfo for scanned index */
          Index *pBest = 0;                    /* Best index found so far */
          Pgno iRoot = pTab->tnum;             /* Root page of scanned b-tree */
  
          sqlite3CodeVerifySchema(pParse, iDb);
          sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);
  
          /* Search for the index that has the lowest scan cost.
          **
          ** (2011-04-15) Do not do a full scan of an unordered index.
          **
          ** (2013-10-03) Do not count the entries in a partial index.
          **
          ** In practice the KeyInfo structure will not be used. It is only 
          ** passed to keep OP_OpenRead happy.
          */
          if( !HasRowid(pTab) ) pBest = sqlite3PrimaryKeyIndex(pTab);
          if( !p->pSrc->a[0].fg.notIndexed ){
            for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
              if( pIdx->bUnordered==0
               && pIdx->szIdxRow<pTab->szTabRow
               && pIdx->pPartIdxWhere==0
               && (!pBest || pIdx->szIdxRow<pBest->szIdxRow)
              ){
                pBest = pIdx;
              }
            }
          }
          if( pBest ){
            iRoot = pBest->tnum;
            pKeyInfo = sqlite3KeyInfoOfIndex(pParse, pBest);
          }
  
          /* Open a read-only cursor, execute the OP_Count, close the cursor. */
          sqlite3VdbeAddOp4Int(v, OP_OpenRead, iCsr, (int)iRoot, iDb, 1);
          if( pKeyInfo ){
            sqlite3VdbeChangeP4(v, -1, (char *)pKeyInfo, P4_KEYINFO);
          }
          sqlite3VdbeAddOp2(v, OP_Count, iCsr, pAggInfo->aFunc[0].iMem);
          sqlite3VdbeAddOp1(v, OP_Close, iCsr);
          explainSimpleCount(pParse, pTab, pBest);
        }else{
          int regAcc = 0;           /* "populate accumulators" flag */
          ExprList *pDistinct = 0;
          u16 distFlag = 0;
          int eDist;
  
          /* If there are accumulator registers but no min() or max() functions
          ** without FILTER clauses, allocate register regAcc. Register regAcc
          ** will contain 0 the first time the inner loop runs, and 1 thereafter.
          ** The code generated by updateAccumulator() uses this to ensure
          ** that the accumulator registers are (a) updated only once if
          ** there are no min() or max functions or (b) always updated for the
          ** first row visited by the aggregate, so that they are updated at
          ** least once even if the FILTER clause means the min() or max() 
          ** function visits zero rows.  */
          if( pAggInfo->nAccumulator ){
            for(i=0; i<pAggInfo->nFunc; i++){
              if( ExprHasProperty(pAggInfo->aFunc[i].pFExpr, EP_WinFunc) ){
                continue;
              }
              if( pAggInfo->aFunc[i].pFunc->funcFlags&SQLITE_FUNC_NEEDCOLL ){
                break;
              }
            }
            if( i==pAggInfo->nFunc ){
              regAcc = ++pParse->nMem;
              sqlite3VdbeAddOp2(v, OP_Integer, 0, regAcc);
            }
          }else if( pAggInfo->nFunc==1 && pAggInfo->aFunc[0].iDistinct>=0 ){
            pDistinct = pAggInfo->aFunc[0].pFExpr->x.pList;
            distFlag = pDistinct ? (WHERE_WANT_DISTINCT|WHERE_AGG_DISTINCT) : 0;
          }
  
          /* This case runs if the aggregate has no GROUP BY clause.  The
          ** processing is much simpler since there is only a single row
          ** of output.
          */
          assert( p->pGroupBy==0 );
          resetAccumulator(pParse, pAggInfo);
  
          /* If this query is a candidate for the min/max optimization, then
          ** minMaxFlag will have been previously set to either
          ** WHERE_ORDERBY_MIN or WHERE_ORDERBY_MAX and pMinMaxOrderBy will
          ** be an appropriate ORDER BY expression for the optimization.
          */
          assert( minMaxFlag==WHERE_ORDERBY_NORMAL || pMinMaxOrderBy!=0 );
          assert( pMinMaxOrderBy==0 || pMinMaxOrderBy->nExpr==1 );
  
          SELECTTRACE(1,pParse,p,("WhereBegin\n"));
          pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, pMinMaxOrderBy,
                                     pDistinct, minMaxFlag|distFlag, 0);
          if( pWInfo==0 ){
            goto select_end;
          }
          SELECTTRACE(1,pParse,p,("WhereBegin returns\n"));
          eDist = sqlite3WhereIsDistinct(pWInfo);
          updateAccumulator(pParse, regAcc, pAggInfo, eDist);
          if( eDist!=WHERE_DISTINCT_NOOP ){
            struct AggInfo_func *pF = &pAggInfo->aFunc[0];
            fixDistinctOpenEph(pParse, eDist, pF->iDistinct, pF->iDistAddr);
          }
  
          if( regAcc ) sqlite3VdbeAddOp2(v, OP_Integer, 1, regAcc);
          if( minMaxFlag ){
            sqlite3WhereMinMaxOptEarlyOut(v, pWInfo);
          }
          SELECTTRACE(1,pParse,p,("WhereEnd\n"));
          sqlite3WhereEnd(pWInfo);
          finalizeAggFunctions(pParse, pAggInfo);
        }
  
        sSort.pOrderBy = 0;
        sqlite3ExprIfFalse(pParse, pHaving, addrEnd, SQLITE_JUMPIFNULL);
        selectInnerLoop(pParse, p, -1, 0, 0, 
                        pDest, addrEnd, addrEnd);
      }
      sqlite3VdbeResolveLabel(v, addrEnd);
      
    } /* endif aggregate query */
  
    if( sDistinct.eTnctType==WHERE_DISTINCT_UNORDERED ){
      explainTempTable(pParse, "DISTINCT");
    }
  
    /* If there is an ORDER BY clause, then we need to sort the results
    ** and send them to the callback one by one.
    */
    if( sSort.pOrderBy ){
      explainTempTable(pParse,
                       sSort.nOBSat>0 ? "RIGHT PART OF ORDER BY":"ORDER BY");
      assert( p->pEList==pEList );
      generateSortTail(pParse, p, &sSort, pEList->nExpr, pDest);
    }
  
    /* Jump here to skip this query
    */
    sqlite3VdbeResolveLabel(v, iEnd);
  
    /* The SELECT has been coded. If there is an error in the Parse structure,
    ** set the return code to 1. Otherwise 0. */
    rc = (pParse->nErr>0);
  
    /* Control jumps to here if an error is encountered above, or upon
    ** successful coding of the SELECT.
    */
  select_end:
    assert( db->mallocFailed==0 || db->mallocFailed==1 );
    pParse->nErr += db->mallocFailed;
    sqlite3ExprListDelete(db, pMinMaxOrderBy);
  #ifdef SQLITE_DEBUG
    if( pAggInfo && !db->mallocFailed ){
      for(i=0; i<pAggInfo->nColumn; i++){
        Expr *pExpr = pAggInfo->aCol[i].pCExpr;
        assert( pExpr!=0 );
        assert( pExpr->pAggInfo==pAggInfo );
        assert( pExpr->iAgg==i );
      }
      for(i=0; i<pAggInfo->nFunc; i++){
        Expr *pExpr = pAggInfo->aFunc[i].pFExpr;
        assert( pExpr!=0 );
        assert( pExpr->pAggInfo==pAggInfo );
        assert( pExpr->iAgg==i );
      }
    }
  #endif
  
  #if SELECTTRACE_ENABLED
    SELECTTRACE(0x1,pParse,p,("end processing\n"));
    if( (sqlite3SelectTrace & 0x2000)!=0 && ExplainQueryPlanParent(pParse)==0 ){
      sqlite3TreeViewSelect(0, p, 0);
    }
  #endif
    ExplainQueryPlanPop(pParse);
    return rc;
  }
  