text: /*
  **
  ** 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 the implementation for TRIGGERs
  */
  #include "sqliteInt.h"
  
  #ifndef SQLITE_OMIT_TRIGGER
  /*
  ** Delete a linked list of TriggerStep structures.
  */
  void sqlite3DeleteTriggerStep(sqlite3 *db, TriggerStep *pTriggerStep){
    while( pTriggerStep ){
      TriggerStep * pTmp = pTriggerStep;
      pTriggerStep = pTriggerStep->pNext;
  
      sqlite3ExprDelete(db, pTmp->pWhere);
      sqlite3ExprListDelete(db, pTmp->pExprList);
      sqlite3SelectDelete(db, pTmp->pSelect);
      sqlite3IdListDelete(db, pTmp->pIdList);
      sqlite3UpsertDelete(db, pTmp->pUpsert);
      sqlite3SrcListDelete(db, pTmp->pFrom);
      sqlite3DbFree(db, pTmp->zSpan);
  
      sqlite3DbFree(db, pTmp);
    }
  }
  
  /*
  ** Given table pTab, return a list of all the triggers attached to 
  ** the table. The list is connected by Trigger.pNext pointers.
  **
  ** All of the triggers on pTab that are in the same database as pTab
  ** are already attached to pTab->pTrigger.  But there might be additional
  ** triggers on pTab in the TEMP schema.  This routine prepends all
  ** TEMP triggers on pTab to the beginning of the pTab->pTrigger list
  ** and returns the combined list.
  **
  ** To state it another way:  This routine returns a list of all triggers
  ** that fire off of pTab.  The list will include any TEMP triggers on
  ** pTab as well as the triggers lised in pTab->pTrigger.
  */
  Trigger *sqlite3TriggerList(Parse *pParse, Table *pTab){
    Schema *pTmpSchema;       /* Schema of the pTab table */
    Trigger *pList;           /* List of triggers to return */
    HashElem *p;              /* Loop variable for TEMP triggers */
  
    if( pParse->disableTriggers ){
      return 0;
    }
    pTmpSchema = pParse->db->aDb[1].pSchema;
    p = sqliteHashFirst(&pTmpSchema->trigHash);
    pList = pTab->pTrigger;
    while( p ){
      Trigger *pTrig = (Trigger *)sqliteHashData(p);
      if( pTrig->pTabSchema==pTab->pSchema
       && pTrig->table
       && 0==sqlite3StrICmp(pTrig->table, pTab->zName)
       && pTrig->pTabSchema!=pTmpSchema
      ){
        pTrig->pNext = pList;
        pList = pTrig;
      }else if( pTrig->op==TK_RETURNING
  #ifndef SQLITE_OMIT_VIRTUALTABLE
                && pParse->db->pVtabCtx==0
  #endif
      ){
        assert( pParse->bReturning );
        assert( &(pParse->u1.pReturning->retTrig) == pTrig );
        pTrig->table = pTab->zName;
        pTrig->pTabSchema = pTab->pSchema;
        pTrig->pNext = pList;
        pList = pTrig;
      }        
      p = sqliteHashNext(p);    
    }
  #if 0
    if( pList ){
      Trigger *pX;
      printf("Triggers for %s:", pTab->zName);
      for(pX=pList; pX; pX=pX->pNext){
        printf(" %s", pX->zName);
      }
      printf("\n");
      fflush(stdout);
    }
  #endif
    return pList;  
  }
  
  /*
  ** This is called by the parser when it sees a CREATE TRIGGER statement
  ** up to the point of the BEGIN before the trigger actions.  A Trigger
  ** structure is generated based on the information available and stored
  ** in pParse->pNewTrigger.  After the trigger actions have been parsed, the
  ** sqlite3FinishTrigger() function is called to complete the trigger
  ** construction process.
  */
  void sqlite3BeginTrigger(
    Parse *pParse,      /* The parse context of the CREATE TRIGGER statement */
    Token *pName1,      /* The name of the trigger */
    Token *pName2,      /* The name of the trigger */
    int tr_tm,          /* One of TK_BEFORE, TK_AFTER, TK_INSTEAD */
    int op,             /* One of TK_INSERT, TK_UPDATE, TK_DELETE */
    IdList *pColumns,   /* column list if this is an UPDATE OF trigger */
    SrcList *pTableName,/* The name of the table/view the trigger applies to */
    Expr *pWhen,        /* WHEN clause */
    int isTemp,         /* True if the TEMPORARY keyword is present */
    int noErr           /* Suppress errors if the trigger already exists */
  ){
    Trigger *pTrigger = 0;  /* The new trigger */
    Table *pTab;            /* Table that the trigger fires off of */
    char *zName = 0;        /* Name of the trigger */
    sqlite3 *db = pParse->db;  /* The database connection */
    int iDb;                /* The database to store the trigger in */
    Token *pName;           /* The unqualified db name */
    DbFixer sFix;           /* State vector for the DB fixer */
  
    assert( pName1!=0 );   /* pName1->z might be NULL, but not pName1 itself */
    assert( pName2!=0 );
    assert( op==TK_INSERT || op==TK_UPDATE || op==TK_DELETE );
    assert( op>0 && op<0xff );
    if( isTemp ){
      /* If TEMP was specified, then the trigger name may not be qualified. */
      if( pName2->n>0 ){
        sqlite3ErrorMsg(pParse, "temporary trigger may not have qualified name");
        goto trigger_cleanup;
      }
      iDb = 1;
      pName = pName1;
    }else{
      /* Figure out the db that the trigger will be created in */
      iDb = sqlite3TwoPartName(pParse, pName1, pName2, &pName);
      if( iDb<0 ){
        goto trigger_cleanup;
      }
    }
    if( !pTableName || db->mallocFailed ){
      goto trigger_cleanup;
    }
  
    /* A long-standing parser bug is that this syntax was allowed:
    **
    **    CREATE TRIGGER attached.demo AFTER INSERT ON attached.tab ....
    **                                                 ^^^^^^^^
    **
    ** To maintain backwards compatibility, ignore the database
    ** name on pTableName if we are reparsing out of the schema table
    */
    if( db->init.busy && iDb!=1 ){
      sqlite3DbFree(db, pTableName->a[0].zDatabase);
      pTableName->a[0].zDatabase = 0;
    }
  
    /* If the trigger name was unqualified, and the table is a temp table,
    ** then set iDb to 1 to create the trigger in the temporary database.
    ** If sqlite3SrcListLookup() returns 0, indicating the table does not
    ** exist, the error is caught by the block below.
    */
    pTab = sqlite3SrcListLookup(pParse, pTableName);
    if( db->init.busy==0 && pName2->n==0 && pTab
          && pTab->pSchema==db->aDb[1].pSchema ){
      iDb = 1;
    }
  
    /* Ensure the table name matches database name and that the table exists */
    if( db->mallocFailed ) goto trigger_cleanup;
    assert( pTableName->nSrc==1 );
    sqlite3FixInit(&sFix, pParse, iDb, "trigger", pName);
    if( sqlite3FixSrcList(&sFix, pTableName) ){
      goto trigger_cleanup;
    }
    pTab = sqlite3SrcListLookup(pParse, pTableName);
    if( !pTab ){
      /* The table does not exist. */
      goto trigger_orphan_error;
    }
    if( IsVirtual(pTab) ){
      sqlite3ErrorMsg(pParse, "cannot create triggers on virtual tables");
      goto trigger_orphan_error;
    }
  
    /* Check that the trigger name is not reserved and that no trigger of the
    ** specified name exists */
    zName = sqlite3NameFromToken(db, pName);
    if( zName==0 ){
      assert( db->mallocFailed );
      goto trigger_cleanup;
    }
    if( sqlite3CheckObjectName(pParse, zName, "trigger", pTab->zName) ){
      goto trigger_cleanup;
    }
    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
    if( !IN_RENAME_OBJECT ){
      if( sqlite3HashFind(&(db->aDb[iDb].pSchema->trigHash),zName) ){
        if( !noErr ){
          sqlite3ErrorMsg(pParse, "trigger %T already exists", pName);
        }else{
          assert( !db->init.busy );
          sqlite3CodeVerifySchema(pParse, iDb);
        }
        goto trigger_cleanup;
      }
    }
  
    /* Do not create a trigger on a system table */
    if( sqlite3StrNICmp(pTab->zName, "sqlite_", 7)==0 ){
      sqlite3ErrorMsg(pParse, "cannot create trigger on system table");
      goto trigger_cleanup;
    }
  
    /* INSTEAD of triggers are only for views and views only support INSTEAD
    ** of triggers.
    */
    if( IsView(pTab) && tr_tm!=TK_INSTEAD ){
      sqlite3ErrorMsg(pParse, "cannot create %s trigger on view: %S", 
          (tr_tm == TK_BEFORE)?"BEFORE":"AFTER", pTableName->a);
      goto trigger_orphan_error;
    }
    if( !IsView(pTab) && tr_tm==TK_INSTEAD ){
      sqlite3ErrorMsg(pParse, "cannot create INSTEAD OF"
          " trigger on table: %S", pTableName->a);
      goto trigger_orphan_error;
    }
  
  #ifndef SQLITE_OMIT_AUTHORIZATION
    if( !IN_RENAME_OBJECT ){
      int iTabDb = sqlite3SchemaToIndex(db, pTab->pSchema);
      int code = SQLITE_CREATE_TRIGGER;
      const char *zDb = db->aDb[iTabDb].zDbSName;
      const char *zDbTrig = isTemp ? db->aDb[1].zDbSName : zDb;
      if( iTabDb==1 || isTemp ) code = SQLITE_CREATE_TEMP_TRIGGER;
      if( sqlite3AuthCheck(pParse, code, zName, pTab->zName, zDbTrig) ){
        goto trigger_cleanup;
      }
      if( sqlite3AuthCheck(pParse, SQLITE_INSERT, SCHEMA_TABLE(iTabDb),0,zDb)){
        goto trigger_cleanup;
      }
    }
  #endif
  
    /* INSTEAD OF triggers can only appear on views and BEFORE triggers
    ** cannot appear on views.  So we might as well translate every
    ** INSTEAD OF trigger into a BEFORE trigger.  It simplifies code
    ** elsewhere.
    */
    if (tr_tm == TK_INSTEAD){
      tr_tm = TK_BEFORE;
    }
  
    /* Build the Trigger object */
    pTrigger = (Trigger*)sqlite3DbMallocZero(db, sizeof(Trigger));
    if( pTrigger==0 ) goto trigger_cleanup;
    pTrigger->zName = zName;
    zName = 0;
    pTrigger->table = sqlite3DbStrDup(db, pTableName->a[0].zName);
    pTrigger->pSchema = db->aDb[iDb].pSchema;
    pTrigger->pTabSchema = pTab->pSchema;
    pTrigger->op = (u8)op;
    pTrigger->tr_tm = tr_tm==TK_BEFORE ? TRIGGER_BEFORE : TRIGGER_AFTER;
    if( IN_RENAME_OBJECT ){
      sqlite3RenameTokenRemap(pParse, pTrigger->table, pTableName->a[0].zName);
      pTrigger->pWhen = pWhen;
      pWhen = 0;
    }else{
      pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
    }
    pTrigger->pColumns = pColumns;
    pColumns = 0;
    assert( pParse->pNewTrigger==0 );
    pParse->pNewTrigger = pTrigger;
  
  trigger_cleanup:
    sqlite3DbFree(db, zName);
    sqlite3SrcListDelete(db, pTableName);
    sqlite3IdListDelete(db, pColumns);
    sqlite3ExprDelete(db, pWhen);
    if( !pParse->pNewTrigger ){
      sqlite3DeleteTrigger(db, pTrigger);
    }else{
      assert( pParse->pNewTrigger==pTrigger );
    }
    return;
  
  trigger_orphan_error:
    if( db->init.iDb==1 ){
      /* Ticket #3810.
      ** Normally, whenever a table is dropped, all associated triggers are
      ** dropped too.  But if a TEMP trigger is created on a non-TEMP table
      ** and the table is dropped by a different database connection, the
      ** trigger is not visible to the database connection that does the
      ** drop so the trigger cannot be dropped.  This results in an
      ** "orphaned trigger" - a trigger whose associated table is missing.
      **
      ** 2020-11-05 see also https://sqlite.org/forum/forumpost/157dc791df
      */
      db->init.orphanTrigger = 1;
    }
    goto trigger_cleanup;
  }
  
  /*
  ** This routine is called after all of the trigger actions have been parsed
  ** in order to complete the process of building the trigger.
  */
  void sqlite3FinishTrigger(
    Parse *pParse,          /* Parser context */
    TriggerStep *pStepList, /* The triggered program */
    Token *pAll             /* Token that describes the complete CREATE TRIGGER */
  ){
    Trigger *pTrig = pParse->pNewTrigger;   /* Trigger being finished */
    char *zName;                            /* Name of trigger */
    sqlite3 *db = pParse->db;               /* The database */
    DbFixer sFix;                           /* Fixer object */
    int iDb;                                /* Database containing the trigger */
    Token nameToken;                        /* Trigger name for error reporting */
  
    pParse->pNewTrigger = 0;
    if( NEVER(pParse->nErr) || !pTrig ) goto triggerfinish_cleanup;
    zName = pTrig->zName;
    iDb = sqlite3SchemaToIndex(pParse->db, pTrig->pSchema);
    pTrig->step_list = pStepList;
    while( pStepList ){
      pStepList->pTrig = pTrig;
      pStepList = pStepList->pNext;
    }
    sqlite3TokenInit(&nameToken, pTrig->zName);
    sqlite3FixInit(&sFix, pParse, iDb, "trigger", &nameToken);
    if( sqlite3FixTriggerStep(&sFix, pTrig->step_list) 
     || sqlite3FixExpr(&sFix, pTrig->pWhen) 
    ){
      goto triggerfinish_cleanup;
    }
  
  #ifndef SQLITE_OMIT_ALTERTABLE
    if( IN_RENAME_OBJECT ){
      assert( !db->init.busy );
      pParse->pNewTrigger = pTrig;
      pTrig = 0;
    }else
  #endif
  
    /* if we are not initializing,
    ** build the sqlite_schema entry
    */
    if( !db->init.busy ){
      Vdbe *v;
      char *z;
  
      /* Make an entry in the sqlite_schema table */
      v = sqlite3GetVdbe(pParse);
      if( v==0 ) goto triggerfinish_cleanup;
      sqlite3BeginWriteOperation(pParse, 0, iDb);
      z = sqlite3DbStrNDup(db, (char*)pAll->z, pAll->n);
      testcase( z==0 );
      sqlite3NestedParse(pParse,
         "INSERT INTO %Q." LEGACY_SCHEMA_TABLE
         " VALUES('trigger',%Q,%Q,0,'CREATE TRIGGER %q')",
         db->aDb[iDb].zDbSName, zName,
         pTrig->table, z);
      sqlite3DbFree(db, z);
      sqlite3ChangeCookie(pParse, iDb);
      sqlite3VdbeAddParseSchemaOp(v, iDb,
          sqlite3MPrintf(db, "type='trigger' AND name='%q'", zName), 0);
    }
  
    if( db->init.busy ){
      Trigger *pLink = pTrig;
      Hash *pHash = &db->aDb[iDb].pSchema->trigHash;
      assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
      assert( pLink!=0 );
      pTrig = sqlite3HashInsert(pHash, zName, pTrig);
      if( pTrig ){
        sqlite3OomFault(db);
      }else if( pLink->pSchema==pLink->pTabSchema ){
        Table *pTab;
        pTab = sqlite3HashFind(&pLink->pTabSchema->tblHash, pLink->table);
        assert( pTab!=0 );
        pLink->pNext = pTab->pTrigger;
        pTab->pTrigger = pLink;
      }
    }
  
  triggerfinish_cleanup:
    sqlite3DeleteTrigger(db, pTrig);
    assert( IN_RENAME_OBJECT || !pParse->pNewTrigger );
    sqlite3DeleteTriggerStep(db, pStepList);
  }
  
  /*
  ** Duplicate a range of text from an SQL statement, then convert all
  ** whitespace characters into ordinary space characters.
  */
  static char *triggerSpanDup(sqlite3 *db, const char *zStart, const char *zEnd){
    char *z = sqlite3DbSpanDup(db, zStart, zEnd);
    int i;
    if( z ) for(i=0; z[i]; i++) if( sqlite3Isspace(z[i]) ) z[i] = ' ';
    return z;
  }    
  
  /*
  ** Turn a SELECT statement (that the pSelect parameter points to) into
  ** a trigger step.  Return a pointer to a TriggerStep structure.
  **
  ** The parser calls this routine when it finds a SELECT statement in
  ** body of a TRIGGER.  
  */
  TriggerStep *sqlite3TriggerSelectStep(
    sqlite3 *db,                /* Database connection */
    Select *pSelect,            /* The SELECT statement */
    const char *zStart,         /* Start of SQL text */
    const char *zEnd            /* End of SQL text */
  ){
    TriggerStep *pTriggerStep = sqlite3DbMallocZero(db, sizeof(TriggerStep));
    if( pTriggerStep==0 ) {
      sqlite3SelectDelete(db, pSelect);
      return 0;
    }
    pTriggerStep->op = TK_SELECT;
    pTriggerStep->pSelect = pSelect;
    pTriggerStep->orconf = OE_Default;
    pTriggerStep->zSpan = triggerSpanDup(db, zStart, zEnd);
    return pTriggerStep;
  }
  
  /*
  ** Allocate space to hold a new trigger step.  The allocated space
  ** holds both the TriggerStep object and the TriggerStep.target.z string.
  **
  ** If an OOM error occurs, NULL is returned and db->mallocFailed is set.
  */
  static TriggerStep *triggerStepAllocate(
    Parse *pParse,              /* Parser context */
    u8 op,                      /* Trigger opcode */
    Token *pName,               /* The target name */
    const char *zStart,         /* Start of SQL text */
    const char *zEnd            /* End of SQL text */
  ){
    sqlite3 *db = pParse->db;
    TriggerStep *pTriggerStep;
  
    pTriggerStep = sqlite3DbMallocZero(db, sizeof(TriggerStep) + pName->n + 1);
    if( pTriggerStep ){
      char *z = (char*)&pTriggerStep[1];
      memcpy(z, pName->z, pName->n);
      sqlite3Dequote(z);
      pTriggerStep->zTarget = z;
      pTriggerStep->op = op;
      pTriggerStep->zSpan = triggerSpanDup(db, zStart, zEnd);
      if( IN_RENAME_OBJECT ){
        sqlite3RenameTokenMap(pParse, pTriggerStep->zTarget, pName);
      }
    }
    return pTriggerStep;
  }
  
  /*
  ** Build a trigger step out of an INSERT statement.  Return a pointer
  ** to the new trigger step.
  **
  ** The parser calls this routine when it sees an INSERT inside the
  ** body of a trigger.
  */
  TriggerStep *sqlite3TriggerInsertStep(
    Parse *pParse,      /* Parser */
    Token *pTableName,  /* Name of the table into which we insert */
    IdList *pColumn,    /* List of columns in pTableName to insert into */
    Select *pSelect,    /* A SELECT statement that supplies values */
    u8 orconf,          /* The conflict algorithm (OE_Abort, OE_Replace, etc.) */
    Upsert *pUpsert,    /* ON CONFLICT clauses for upsert */
    const char *zStart, /* Start of SQL text */
    const char *zEnd    /* End of SQL text */
  ){
    sqlite3 *db = pParse->db;
    TriggerStep *pTriggerStep;
  
    assert(pSelect != 0 || db->mallocFailed);
  
    pTriggerStep = triggerStepAllocate(pParse, TK_INSERT, pTableName,zStart,zEnd);
    if( pTriggerStep ){
      if( IN_RENAME_OBJECT ){
        pTriggerStep->pSelect = pSelect;
        pSelect = 0;
      }else{
        pTriggerStep->pSelect = sqlite3SelectDup(db, pSelect, EXPRDUP_REDUCE);
      }
      pTriggerStep->pIdList = pColumn;
      pTriggerStep->pUpsert = pUpsert;
      pTriggerStep->orconf = orconf;
      if( pUpsert ){
        sqlite3HasExplicitNulls(pParse, pUpsert->pUpsertTarget);
      }
    }else{
      testcase( pColumn );
      sqlite3IdListDelete(db, pColumn);
      testcase( pUpsert );
      sqlite3UpsertDelete(db, pUpsert);
    }
    sqlite3SelectDelete(db, pSelect);
  
    return pTriggerStep;
  }
  
  /*
  ** Construct a trigger step that implements an UPDATE statement and return
  ** a pointer to that trigger step.  The parser calls this routine when it
  ** sees an UPDATE statement inside the body of a CREATE TRIGGER.
  */
  TriggerStep *sqlite3TriggerUpdateStep(
    Parse *pParse,          /* Parser */
    Token *pTableName,   /* Name of the table to be updated */
    SrcList *pFrom,
    ExprList *pEList,    /* The SET clause: list of column and new values */
    Expr *pWhere,        /* The WHERE clause */
    u8 orconf,           /* The conflict algorithm. (OE_Abort, OE_Ignore, etc) */
    const char *zStart,  /* Start of SQL text */
    const char *zEnd     /* End of SQL text */
  ){
    sqlite3 *db = pParse->db;
    TriggerStep *pTriggerStep;
  
    pTriggerStep = triggerStepAllocate(pParse, TK_UPDATE, pTableName,zStart,zEnd);
    if( pTriggerStep ){
      if( IN_RENAME_OBJECT ){
        pTriggerStep->pExprList = pEList;
        pTriggerStep->pWhere = pWhere;
        pTriggerStep->pFrom = pFrom;
        pEList = 0;
        pWhere = 0;
        pFrom = 0;
      }else{
        pTriggerStep->pExprList = sqlite3ExprListDup(db, pEList, EXPRDUP_REDUCE);
        pTriggerStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
        pTriggerStep->pFrom = sqlite3SrcListDup(db, pFrom, EXPRDUP_REDUCE);
      }
      pTriggerStep->orconf = orconf;
    }
    sqlite3ExprListDelete(db, pEList);
    sqlite3ExprDelete(db, pWhere);
    sqlite3SrcListDelete(db, pFrom);
    return pTriggerStep;
  }
  
  /*
  ** Construct a trigger step that implements a DELETE statement and return
  ** a pointer to that trigger step.  The parser calls this routine when it
  ** sees a DELETE statement inside the body of a CREATE TRIGGER.
  */
  TriggerStep *sqlite3TriggerDeleteStep(
    Parse *pParse,          /* Parser */
    Token *pTableName,      /* The table from which rows are deleted */
    Expr *pWhere,           /* The WHERE clause */
    const char *zStart,     /* Start of SQL text */
    const char *zEnd        /* End of SQL text */
  ){
    sqlite3 *db = pParse->db;
    TriggerStep *pTriggerStep;
  
    pTriggerStep = triggerStepAllocate(pParse, TK_DELETE, pTableName,zStart,zEnd);
    if( pTriggerStep ){
      if( IN_RENAME_OBJECT ){
        pTriggerStep->pWhere = pWhere;
        pWhere = 0;
      }else{
        pTriggerStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
      }
      pTriggerStep->orconf = OE_Default;
    }
    sqlite3ExprDelete(db, pWhere);
    return pTriggerStep;
  }
  
  /* 
  ** Recursively delete a Trigger structure
  */
  void sqlite3DeleteTrigger(sqlite3 *db, Trigger *pTrigger){
    if( pTrigger==0 || pTrigger->bReturning ) return;
    sqlite3DeleteTriggerStep(db, pTrigger->step_list);
    sqlite3DbFree(db, pTrigger->zName);
    sqlite3DbFree(db, pTrigger->table);
    sqlite3ExprDelete(db, pTrigger->pWhen);
    sqlite3IdListDelete(db, pTrigger->pColumns);
    sqlite3DbFree(db, pTrigger);
  }
  
  /*
  ** This function is called to drop a trigger from the database schema. 
  **
  ** This may be called directly from the parser and therefore identifies
  ** the trigger by name.  The sqlite3DropTriggerPtr() routine does the
  ** same job as this routine except it takes a pointer to the trigger
  ** instead of the trigger name.
  **/
  void sqlite3DropTrigger(Parse *pParse, SrcList *pName, int noErr){
    Trigger *pTrigger = 0;
    int i;
    const char *zDb;
    const char *zName;
    sqlite3 *db = pParse->db;
  
    if( db->mallocFailed ) goto drop_trigger_cleanup;
    if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
      goto drop_trigger_cleanup;
    }
  
    assert( pName->nSrc==1 );
    zDb = pName->a[0].zDatabase;
    zName = pName->a[0].zName;
    assert( zDb!=0 || sqlite3BtreeHoldsAllMutexes(db) );
    for(i=OMIT_TEMPDB; i<db->nDb; i++){
      int j = (i<2) ? i^1 : i;  /* Search TEMP before MAIN */
      if( zDb && sqlite3DbIsNamed(db, j, zDb)==0 ) continue;
      assert( sqlite3SchemaMutexHeld(db, j, 0) );
      pTrigger = sqlite3HashFind(&(db->aDb[j].pSchema->trigHash), zName);
      if( pTrigger ) break;
    }
    if( !pTrigger ){
      if( !noErr ){
        sqlite3ErrorMsg(pParse, "no such trigger: %S", pName->a);
      }else{
        sqlite3CodeVerifyNamedSchema(pParse, zDb);
      }
      pParse->checkSchema = 1;
      goto drop_trigger_cleanup;
    }
    sqlite3DropTriggerPtr(pParse, pTrigger);
  
  drop_trigger_cleanup:
    sqlite3SrcListDelete(db, pName);
  }
  
  /*
  ** Return a pointer to the Table structure for the table that a trigger
  ** is set on.
  */
  static Table *tableOfTrigger(Trigger *pTrigger){
    return sqlite3HashFind(&pTrigger->pTabSchema->tblHash, pTrigger->table);
  }
  
  
  /*
  ** Drop a trigger given a pointer to that trigger. 
  */
  void sqlite3DropTriggerPtr(Parse *pParse, Trigger *pTrigger){
    Table   *pTable;
    Vdbe *v;
    sqlite3 *db = pParse->db;
    int iDb;
  
    iDb = sqlite3SchemaToIndex(pParse->db, pTrigger->pSchema);
    assert( iDb>=0 && iDb<db->nDb );
    pTable = tableOfTrigger(pTrigger);
    assert( (pTable && pTable->pSchema==pTrigger->pSchema) || iDb==1 );
  #ifndef SQLITE_OMIT_AUTHORIZATION
    if( pTable ){
      int code = SQLITE_DROP_TRIGGER;
      const char *zDb = db->aDb[iDb].zDbSName;
      const char *zTab = SCHEMA_TABLE(iDb);
      if( iDb==1 ) code = SQLITE_DROP_TEMP_TRIGGER;
      if( sqlite3AuthCheck(pParse, code, pTrigger->zName, pTable->zName, zDb) ||
        sqlite3AuthCheck(pParse, SQLITE_DELETE, zTab, 0, zDb) ){
        return;
      }
    }
  #endif
  
    /* Generate code to destroy the database record of the trigger.
    */
    if( (v = sqlite3GetVdbe(pParse))!=0 ){
      sqlite3NestedParse(pParse,
         "DELETE FROM %Q." LEGACY_SCHEMA_TABLE " WHERE name=%Q AND type='trigger'",
         db->aDb[iDb].zDbSName, pTrigger->zName
      );
      sqlite3ChangeCookie(pParse, iDb);
      sqlite3VdbeAddOp4(v, OP_DropTrigger, iDb, 0, 0, pTrigger->zName, 0);
    }
  }
  
  /*
  ** Remove a trigger from the hash tables of the sqlite* pointer.
  */
  void sqlite3UnlinkAndDeleteTrigger(sqlite3 *db, int iDb, const char *zName){
    Trigger *pTrigger;
    Hash *pHash;
  
    assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
    pHash = &(db->aDb[iDb].pSchema->trigHash);
    pTrigger = sqlite3HashInsert(pHash, zName, 0);
    if( ALWAYS(pTrigger) ){
      if( pTrigger->pSchema==pTrigger->pTabSchema ){
        Table *pTab = tableOfTrigger(pTrigger);
        if( pTab ){
          Trigger **pp;
          for(pp=&pTab->pTrigger; *pp; pp=&((*pp)->pNext)){
            if( *pp==pTrigger ){
              *pp = (*pp)->pNext;
              break;
            }
          }
        }
      }
      sqlite3DeleteTrigger(db, pTrigger);
      db->mDbFlags |= DBFLAG_SchemaChange;
    }
  }
  
  /*
  ** pEList is the SET clause of an UPDATE statement.  Each entry
  ** in pEList is of the format <id>=<expr>.  If any of the entries
  ** in pEList have an <id> which matches an identifier in pIdList,
  ** then return TRUE.  If pIdList==NULL, then it is considered a
  ** wildcard that matches anything.  Likewise if pEList==NULL then
  ** it matches anything so always return true.  Return false only
  ** if there is no match.
  */
  static int checkColumnOverlap(IdList *pIdList, ExprList *pEList){
    int e;
    if( pIdList==0 || NEVER(pEList==0) ) return 1;
    for(e=0; e<pEList->nExpr; e++){
      if( sqlite3IdListIndex(pIdList, pEList->a[e].zEName)>=0 ) return 1;
    }
    return 0; 
  }
  
  /*
  ** Return a list of all triggers on table pTab if there exists at least
  ** one trigger that must be fired when an operation of type 'op' is 
  ** performed on the table, and, if that operation is an UPDATE, if at
  ** least one of the columns in pChanges is being modified.
  */
  Trigger *sqlite3TriggersExist(
    Parse *pParse,          /* Parse context */
    Table *pTab,            /* The table the contains the triggers */
    int op,                 /* one of TK_DELETE, TK_INSERT, TK_UPDATE */
    ExprList *pChanges,     /* Columns that change in an UPDATE statement */
    int *pMask              /* OUT: Mask of TRIGGER_BEFORE|TRIGGER_AFTER */
  ){
    int mask = 0;
    Trigger *pList = 0;
    Trigger *p;
  
    pList = sqlite3TriggerList(pParse, pTab);
    assert( pList==0 || IsVirtual(pTab)==0 
             || (pList->bReturning && pList->pNext==0) );
    if( pList!=0 ){
      p = pList;
      if( (pParse->db->flags & SQLITE_EnableTrigger)==0
       && pTab->pTrigger!=0
      ){
        /* The SQLITE_DBCONFIG_ENABLE_TRIGGER setting is off.  That means that
        ** only TEMP triggers are allowed.  Truncate the pList so that it
        ** includes only TEMP triggers */
        if( pList==pTab->pTrigger ){
          pList = 0;
          goto exit_triggers_exist;
        }
        while( ALWAYS(p->pNext) && p->pNext!=pTab->pTrigger ) p = p->pNext;
        p->pNext = 0;
        p = pList;
      }
      do{
        if( p->op==op && checkColumnOverlap(p->pColumns, pChanges) ){
          mask |= p->tr_tm;
        }else if( p->op==TK_RETURNING ){
          /* The first time a RETURNING trigger is seen, the "op" value tells
          ** us what time of trigger it should be. */
          assert( sqlite3IsToplevel(pParse) );
          p->op = op;
          if( IsVirtual(pTab) ){
            if( op!=TK_INSERT ){
              sqlite3ErrorMsg(pParse,
                "%s RETURNING is not available on virtual tables",
                op==TK_DELETE ? "DELETE" : "UPDATE");
            }
            p->tr_tm = TRIGGER_BEFORE;
          }else{
            p->tr_tm = TRIGGER_AFTER;
          }
          mask |= p->tr_tm;
        }else if( p->bReturning && p->op==TK_INSERT && op==TK_UPDATE
                  && sqlite3IsToplevel(pParse) ){
          /* Also fire a RETURNING trigger for an UPSERT */
          mask |= p->tr_tm;
        }
        p = p->pNext;
      }while( p );
    }
  exit_triggers_exist:
    if( pMask ){
      *pMask = mask;
    }
    return (mask ? pList : 0);
  }
  
  /*
  ** Convert the pStep->zTarget string into a SrcList and return a pointer
  ** to that SrcList.
  **
  ** This routine adds a specific database name, if needed, to the target when
  ** forming the SrcList.  This prevents a trigger in one database from
  ** referring to a target in another database.  An exception is when the
  ** trigger is in TEMP in which case it can refer to any other database it
  ** wants.
  */
  SrcList *sqlite3TriggerStepSrc(
    Parse *pParse,       /* The parsing context */
    TriggerStep *pStep   /* The trigger containing the target token */
  ){
    sqlite3 *db = pParse->db;
    SrcList *pSrc;                  /* SrcList to be returned */
    char *zName = sqlite3DbStrDup(db, pStep->zTarget);
    pSrc = sqlite3SrcListAppend(pParse, 0, 0, 0);
    assert( pSrc==0 || pSrc->nSrc==1 );
    assert( zName || pSrc==0 );
    if( pSrc ){
      Schema *pSchema = pStep->pTrig->pSchema;
      pSrc->a[0].zName = zName;
      if( pSchema!=db->aDb[1].pSchema ){
        pSrc->a[0].pSchema = pSchema;
      }
      if( pStep->pFrom ){
        SrcList *pDup = sqlite3SrcListDup(db, pStep->pFrom, 0);
        pSrc = sqlite3SrcListAppendList(pParse, pSrc, pDup);
      }
    }else{
      sqlite3DbFree(db, zName);
    }
    return pSrc;
  }
  
  /*
  ** Return true if the pExpr term from the RETURNING clause argument
  ** list is of the form "*".  Raise an error if the terms if of the
  ** form "table.*".
  */
  static int isAsteriskTerm(
    Parse *pParse,      /* Parsing context */
    Expr *pTerm         /* A term in the RETURNING clause */
  ){
    assert( pTerm!=0 );
    if( pTerm->op==TK_ASTERISK ) return 1;
    if( pTerm->op!=TK_DOT ) return 0;
    assert( pTerm->pRight!=0 );
    assert( pTerm->pLeft!=0 );
    if( pTerm->pRight->op!=TK_ASTERISK ) return 0;
    sqlite3ErrorMsg(pParse, "RETURNING may not use \"TABLE.*\" wildcards");
    return 1;
  }
  
  /* The input list pList is the list of result set terms from a RETURNING
  ** clause.  The table that we are returning from is pTab.
  **
  ** This routine makes a copy of the pList, and at the same time expands
  ** any "*" wildcards to be the complete set of columns from pTab.
  */
  static ExprList *sqlite3ExpandReturning(
    Parse *pParse,        /* Parsing context */
    ExprList *pList,      /* The arguments to RETURNING */
    Table *pTab           /* The table being updated */
  ){
    ExprList *pNew = 0;
    sqlite3 *db = pParse->db;
    int i;
  
    for(i=0; i<pList->nExpr; i++){
      Expr *pOldExpr = pList->a[i].pExpr;
      if( NEVER(pOldExpr==0) ) continue;
      if( isAsteriskTerm(pParse, pOldExpr) ){
        int jj;
        for(jj=0; jj<pTab->nCol; jj++){
          Expr *pNewExpr;
          if( IsHiddenColumn(pTab->aCol+jj) ) continue;
          pNewExpr = sqlite3Expr(db, TK_ID, pTab->aCol[jj].zCnName);
          pNew = sqlite3ExprListAppend(pParse, pNew, pNewExpr);
          if( !db->mallocFailed ){
            struct ExprList_item *pItem = &pNew->a[pNew->nExpr-1];
            pItem->zEName = sqlite3DbStrDup(db, pTab->aCol[jj].zCnName);
            pItem->eEName = ENAME_NAME;
          }
        }
      }else{
        Expr *pNewExpr = sqlite3ExprDup(db, pOldExpr, 0);
        pNew = sqlite3ExprListAppend(pParse, pNew, pNewExpr);
        if( !db->mallocFailed && ALWAYS(pList->a[i].zEName!=0) ){
          struct ExprList_item *pItem = &pNew->a[pNew->nExpr-1];
          pItem->zEName = sqlite3DbStrDup(db, pList->a[i].zEName);
          pItem->eEName = pList->a[i].eEName;
        }
      }
    }
    return pNew;
  }
  
  /*
  ** Generate code for the RETURNING trigger.  Unlike other triggers
  ** that invoke a subprogram in the bytecode, the code for RETURNING
  ** is generated in-line.
  */
  static void codeReturningTrigger(
    Parse *pParse,       /* Parse context */
    Trigger *pTrigger,   /* The trigger step that defines the RETURNING */
    Table *pTab,         /* The table to code triggers from */
    int regIn            /* The first in an array of registers */
  ){
    Vdbe *v = pParse->pVdbe;
    sqlite3 *db = pParse->db;
    ExprList *pNew;
    Returning *pReturning;
    Select sSelect;
    SrcList sFrom;
  
    assert( v!=0 );
    assert( pParse->bReturning );
    pReturning = pParse->u1.pReturning;
    assert( pTrigger == &(pReturning->retTrig) );
    memset(&sSelect, 0, sizeof(sSelect));
    memset(&sFrom, 0, sizeof(sFrom));
    sSelect.pEList = sqlite3ExprListDup(db, pReturning->pReturnEL, 0);
    sSelect.pSrc = &sFrom;
    sFrom.nSrc = 1;
    sFrom.a[0].pTab = pTab;
    sFrom.a[0].iCursor = -1;
    sqlite3SelectPrep(pParse, &sSelect, 0);
    if( db->mallocFailed==0 && pParse->nErr==0 ){
      sqlite3GenerateColumnNames(pParse, &sSelect);
    }
    sqlite3ExprListDelete(db, sSelect.pEList);
    pNew = sqlite3ExpandReturning(pParse, pReturning->pReturnEL, pTab);
    if( pNew ){
      NameContext sNC;
      memset(&sNC, 0, sizeof(sNC));
      if( pReturning->nRetCol==0 ){
        pReturning->nRetCol = pNew->nExpr;
        pReturning->iRetCur = pParse->nTab++;
      }
      sNC.pParse = pParse;
      sNC.uNC.iBaseReg = regIn;
      sNC.ncFlags = NC_UBaseReg;
      pParse->eTriggerOp = pTrigger->op;
      pParse->pTriggerTab = pTab;
      if( sqlite3ResolveExprListNames(&sNC, pNew)==SQLITE_OK ){
        int i;
        int nCol = pNew->nExpr;
        int reg = pParse->nMem+1;
        pParse->nMem += nCol+2;
        pReturning->iRetReg = reg;
        for(i=0; i<nCol; i++){
          Expr *pCol = pNew->a[i].pExpr;
          sqlite3ExprCodeFactorable(pParse, pCol, reg+i);
        }
        sqlite3VdbeAddOp3(v, OP_MakeRecord, reg, i, reg+i);
        sqlite3VdbeAddOp2(v, OP_NewRowid, pReturning->iRetCur, reg+i+1);
        sqlite3VdbeAddOp3(v, OP_Insert, pReturning->iRetCur, reg+i, reg+i+1);
      }
      sqlite3ExprListDelete(db, pNew);
      pParse->eTriggerOp = 0;
      pParse->pTriggerTab = 0;
    }
  }
  
  
  
  /*
  ** Generate VDBE code for the statements inside the body of a single 
  ** trigger.
  */
  static int codeTriggerProgram(
    Parse *pParse,            /* The parser context */
    TriggerStep *pStepList,   /* List of statements inside the trigger body */
    int orconf                /* Conflict algorithm. (OE_Abort, etc) */  
  ){
    TriggerStep *pStep;
    Vdbe *v = pParse->pVdbe;
    sqlite3 *db = pParse->db;
  
    assert( pParse->pTriggerTab && pParse->pToplevel );
    assert( pStepList );
    assert( v!=0 );
    for(pStep=pStepList; pStep; pStep=pStep->pNext){
      /* Figure out the ON CONFLICT policy that will be used for this step
      ** of the trigger program. If the statement that caused this trigger
      ** to fire had an explicit ON CONFLICT, then use it. Otherwise, use
      ** the ON CONFLICT policy that was specified as part of the trigger
      ** step statement. Example:
      **
      **   CREATE TRIGGER AFTER INSERT ON t1 BEGIN;
      **     INSERT OR REPLACE INTO t2 VALUES(new.a, new.b);
      **   END;
      **
      **   INSERT INTO t1 ... ;            -- insert into t2 uses REPLACE policy
      **   INSERT OR IGNORE INTO t1 ... ;  -- insert into t2 uses IGNORE policy
      */
      pParse->eOrconf = (orconf==OE_Default)?pStep->orconf:(u8)orconf;
      assert( pParse->okConstFactor==0 );
  
  #ifndef SQLITE_OMIT_TRACE
      if( pStep->zSpan ){
        sqlite3VdbeAddOp4(v, OP_Trace, 0x7fffffff, 1, 0,
                          sqlite3MPrintf(db, "-- %s", pStep->zSpan),
                          P4_DYNAMIC);
      }
  #endif
  
      switch( pStep->op ){
        case TK_UPDATE: {
          sqlite3Update(pParse, 
            sqlite3TriggerStepSrc(pParse, pStep),
            sqlite3ExprListDup(db, pStep->pExprList, 0), 
            sqlite3ExprDup(db, pStep->pWhere, 0), 
            pParse->eOrconf, 0, 0, 0
          );
          sqlite3VdbeAddOp0(v, OP_ResetCount);
          break;
        }
        case TK_INSERT: {
          sqlite3Insert(pParse, 
            sqlite3TriggerStepSrc(pParse, pStep),
            sqlite3SelectDup(db, pStep->pSelect, 0), 
            sqlite3IdListDup(db, pStep->pIdList), 
            pParse->eOrconf,
            sqlite3UpsertDup(db, pStep->pUpsert)
          );
          sqlite3VdbeAddOp0(v, OP_ResetCount);
          break;
        }
        case TK_DELETE: {
          sqlite3DeleteFrom(pParse, 
            sqlite3TriggerStepSrc(pParse, pStep),
            sqlite3ExprDup(db, pStep->pWhere, 0), 0, 0
          );
          sqlite3VdbeAddOp0(v, OP_ResetCount);
          break;
        }
        default: assert( pStep->op==TK_SELECT ); {
          SelectDest sDest;
          Select *pSelect = sqlite3SelectDup(db, pStep->pSelect, 0);
          sqlite3SelectDestInit(&sDest, SRT_Discard, 0);
          sqlite3Select(pParse, pSelect, &sDest);
          sqlite3SelectDelete(db, pSelect);
          break;
        }
      } 
    }
  
    return 0;
  }
  
  #ifdef SQLITE_ENABLE_EXPLAIN_COMMENTS
  /*
  ** This function is used to add VdbeComment() annotations to a VDBE
  ** program. It is not used in production code, only for debugging.
  */
  static const char *onErrorText(int onError){
    switch( onError ){
      case OE_Abort:    return "abort";
      case OE_Rollback: return "rollback";
      case OE_Fail:     return "fail";
      case OE_Replace:  return "replace";
      case OE_Ignore:   return "ignore";
      case OE_Default:  return "default";
    }
    return "n/a";
  }
  #endif
  
  /*
  ** Parse context structure pFrom has just been used to create a sub-vdbe
  ** (trigger program). If an error has occurred, transfer error information
  ** from pFrom to pTo.
  */
  static void transferParseError(Parse *pTo, Parse *pFrom){
    assert( pFrom->zErrMsg==0 || pFrom->nErr );
    assert( pTo->zErrMsg==0 || pTo->nErr );
    if( pTo->nErr==0 ){
      pTo->zErrMsg = pFrom->zErrMsg;
      pTo->nErr = pFrom->nErr;
      pTo->rc = pFrom->rc;
    }else{
      sqlite3DbFree(pFrom->db, pFrom->zErrMsg);
    }
  }
  
  /*
  ** Create and populate a new TriggerPrg object with a sub-program 
  ** implementing trigger pTrigger with ON CONFLICT policy orconf.
  */
  static TriggerPrg *codeRowTrigger(
    Parse *pParse,       /* Current parse context */
    Trigger *pTrigger,   /* Trigger to code */
    Table *pTab,         /* The table pTrigger is attached to */
    int orconf           /* ON CONFLICT policy to code trigger program with */
  ){
    Parse *pTop = sqlite3ParseToplevel(pParse);
    sqlite3 *db = pParse->db;   /* Database handle */
    TriggerPrg *pPrg;           /* Value to return */
    Expr *pWhen = 0;            /* Duplicate of trigger WHEN expression */
    Vdbe *v;                    /* Temporary VM */
    NameContext sNC;            /* Name context for sub-vdbe */
    SubProgram *pProgram = 0;   /* Sub-vdbe for trigger program */
    Parse *pSubParse;           /* Parse context for sub-vdbe */
    int iEndTrigger = 0;        /* Label to jump to if WHEN is false */
  
    assert( pTrigger->zName==0 || pTab==tableOfTrigger(pTrigger) );
    assert( pTop->pVdbe );
  
    /* Allocate the TriggerPrg and SubProgram objects. To ensure that they
    ** are freed if an error occurs, link them into the Parse.pTriggerPrg 
    ** list of the top-level Parse object sooner rather than later.  */
    pPrg = sqlite3DbMallocZero(db, sizeof(TriggerPrg));
    if( !pPrg ) return 0;
    pPrg->pNext = pTop->pTriggerPrg;
    pTop->pTriggerPrg = pPrg;
    pPrg->pProgram = pProgram = sqlite3DbMallocZero(db, sizeof(SubProgram));
    if( !pProgram ) return 0;
    sqlite3VdbeLinkSubProgram(pTop->pVdbe, pProgram);
    pPrg->pTrigger = pTrigger;
    pPrg->orconf = orconf;
    pPrg->aColmask[0] = 0xffffffff;
    pPrg->aColmask[1] = 0xffffffff;
  
    /* Allocate and populate a new Parse context to use for coding the 
    ** trigger sub-program.  */
    pSubParse = sqlite3StackAllocZero(db, sizeof(Parse));
    if( !pSubParse ) return 0;
    memset(&sNC, 0, sizeof(sNC));
    sNC.pParse = pSubParse;
    pSubParse->db = db;
    pSubParse->pTriggerTab = pTab;
    pSubParse->pToplevel = pTop;
    pSubParse->zAuthContext = pTrigger->zName;
    pSubParse->eTriggerOp = pTrigger->op;
    pSubParse->nQueryLoop = pParse->nQueryLoop;
    pSubParse->disableVtab = pParse->disableVtab;
  
    v = sqlite3GetVdbe(pSubParse);
    if( v ){
      VdbeComment((v, "Start: %s.%s (%s %s%s%s ON %s)", 
        pTrigger->zName, onErrorText(orconf),
        (pTrigger->tr_tm==TRIGGER_BEFORE ? "BEFORE" : "AFTER"),
          (pTrigger->op==TK_UPDATE ? "UPDATE" : ""),
          (pTrigger->op==TK_INSERT ? "INSERT" : ""),
          (pTrigger->op==TK_DELETE ? "DELETE" : ""),
        pTab->zName
      ));
  #ifndef SQLITE_OMIT_TRACE
      if( pTrigger->zName ){
        sqlite3VdbeChangeP4(v, -1, 
          sqlite3MPrintf(db, "-- TRIGGER %s", pTrigger->zName), P4_DYNAMIC
        );
      }
  #endif
  
      /* If one was specified, code the WHEN clause. If it evaluates to false
      ** (or NULL) the sub-vdbe is immediately halted by jumping to the 
      ** OP_Halt inserted at the end of the program.  */
      if( pTrigger->pWhen ){
        pWhen = sqlite3ExprDup(db, pTrigger->pWhen, 0);
        if( db->mallocFailed==0
         && SQLITE_OK==sqlite3ResolveExprNames(&sNC, pWhen) 
        ){
          iEndTrigger = sqlite3VdbeMakeLabel(pSubParse);
          sqlite3ExprIfFalse(pSubParse, pWhen, iEndTrigger, SQLITE_JUMPIFNULL);
        }
        sqlite3ExprDelete(db, pWhen);
      }
  
      /* Code the trigger program into the sub-vdbe. */
      codeTriggerProgram(pSubParse, pTrigger->step_list, orconf);
  
      /* Insert an OP_Halt at the end of the sub-program. */
      if( iEndTrigger ){
        sqlite3VdbeResolveLabel(v, iEndTrigger);
      }
      sqlite3VdbeAddOp0(v, OP_Halt);
      VdbeComment((v, "End: %s.%s", pTrigger->zName, onErrorText(orconf)));
  
      transferParseError(pParse, pSubParse);
      if( db->mallocFailed==0 && pParse->nErr==0 ){
        pProgram->aOp = sqlite3VdbeTakeOpArray(v, &pProgram->nOp, &pTop->nMaxArg);
      }
      pProgram->nMem = pSubParse->nMem;
      pProgram->nCsr = pSubParse->nTab;
      pProgram->token = (void *)pTrigger;
      pPrg->aColmask[0] = pSubParse->oldmask;
      pPrg->aColmask[1] = pSubParse->newmask;
      sqlite3VdbeDelete(v);
    }
  
    assert( !pSubParse->pTriggerPrg && !pSubParse->nMaxArg );
    sqlite3ParserReset(pSubParse);
    sqlite3StackFree(db, pSubParse);
  
    return pPrg;
  }
      
  /*
  ** Return a pointer to a TriggerPrg object containing the sub-program for
  ** trigger pTrigger with default ON CONFLICT algorithm orconf. If no such
  ** TriggerPrg object exists, a new object is allocated and populated before
  ** being returned.
  */
  static TriggerPrg *getRowTrigger(
    Parse *pParse,       /* Current parse context */
    Trigger *pTrigger,   /* Trigger to code */
    Table *pTab,         /* The table trigger pTrigger is attached to */
    int orconf           /* ON CONFLICT algorithm. */
  ){
    Parse *pRoot = sqlite3ParseToplevel(pParse);
    TriggerPrg *pPrg;
  
    assert( pTrigger->zName==0 || pTab==tableOfTrigger(pTrigger) );
  
    /* It may be that this trigger has already been coded (or is in the
    ** process of being coded). If this is the case, then an entry with
    ** a matching TriggerPrg.pTrigger field will be present somewhere
    ** in the Parse.pTriggerPrg list. Search for such an entry.  */
    for(pPrg=pRoot->pTriggerPrg; 
        pPrg && (pPrg->pTrigger!=pTrigger || pPrg->orconf!=orconf); 
        pPrg=pPrg->pNext
    );
  
    /* If an existing TriggerPrg could not be located, create a new one. */
    if( !pPrg ){
      pPrg = codeRowTrigger(pParse, pTrigger, pTab, orconf);
    }
  
    return pPrg;
  }
  
  /*
  ** Generate code for the trigger program associated with trigger p on 
  ** table pTab. The reg, orconf and ignoreJump parameters passed to this
  ** function are the same as those described in the header function for
  ** sqlite3CodeRowTrigger()
  */
  void sqlite3CodeRowTriggerDirect(
    Parse *pParse,       /* Parse context */
    Trigger *p,          /* Trigger to code */
    Table *pTab,         /* The table to code triggers from */
    int reg,             /* Reg array containing OLD.* and NEW.* values */
    int orconf,          /* ON CONFLICT policy */
    int ignoreJump       /* Instruction to jump to for RAISE(IGNORE) */
  ){
    Vdbe *v = sqlite3GetVdbe(pParse); /* Main VM */
    TriggerPrg *pPrg;
    pPrg = getRowTrigger(pParse, p, pTab, orconf);
    assert( pPrg || pParse->nErr || pParse->db->mallocFailed );
  
    /* Code the OP_Program opcode in the parent VDBE. P4 of the OP_Program 
    ** is a pointer to the sub-vdbe containing the trigger program.  */
    if( pPrg ){
      int bRecursive = (p->zName && 0==(pParse->db->flags&SQLITE_RecTriggers));
  
      sqlite3VdbeAddOp4(v, OP_Program, reg, ignoreJump, ++pParse->nMem,
                        (const char *)pPrg->pProgram, P4_SUBPROGRAM);
      VdbeComment(
          (v, "Call: %s.%s", (p->zName?p->zName:"fkey"), onErrorText(orconf)));
  
      /* Set the P5 operand of the OP_Program instruction to non-zero if
      ** recursive invocation of this trigger program is disallowed. Recursive
      ** invocation is disallowed if (a) the sub-program is really a trigger,
      ** not a foreign key action, and (b) the flag to enable recursive triggers
      ** is clear.  */
      sqlite3VdbeChangeP5(v, (u8)bRecursive);
    }
  }
  
  /*
  ** This is called to code the required FOR EACH ROW triggers for an operation
  ** on table pTab. The operation to code triggers for (INSERT, UPDATE or DELETE)
  ** is given by the op parameter. The tr_tm parameter determines whether the
  ** BEFORE or AFTER triggers are coded. If the operation is an UPDATE, then
  ** parameter pChanges is passed the list of columns being modified.
  **
  ** If there are no triggers that fire at the specified time for the specified
  ** operation on pTab, this function is a no-op.
  **
  ** The reg argument is the address of the first in an array of registers 
  ** that contain the values substituted for the new.* and old.* references
  ** in the trigger program. If N is the number of columns in table pTab
  ** (a copy of pTab->nCol), then registers are populated as follows:
  **
  **   Register       Contains
  **   ------------------------------------------------------
  **   reg+0          OLD.rowid
  **   reg+1          OLD.* value of left-most column of pTab
  **   ...            ...
  **   reg+N          OLD.* value of right-most column of pTab
  **   reg+N+1        NEW.rowid
  **   reg+N+2        NEW.* value of left-most column of pTab
  **   ...            ...
  **   reg+N+N+1      NEW.* value of right-most column of pTab
  **
  ** For ON DELETE triggers, the registers containing the NEW.* values will
  ** never be accessed by the trigger program, so they are not allocated or 
  ** populated by the caller (there is no data to populate them with anyway). 
  ** Similarly, for ON INSERT triggers the values stored in the OLD.* registers
  ** are never accessed, and so are not allocated by the caller. So, for an
  ** ON INSERT trigger, the value passed to this function as parameter reg
  ** is not a readable register, although registers (reg+N) through 
  ** (reg+N+N+1) are.
  **
  ** Parameter orconf is the default conflict resolution algorithm for the
  ** trigger program to use (REPLACE, IGNORE etc.). Parameter ignoreJump
  ** is the instruction that control should jump to if a trigger program
  ** raises an IGNORE exception.
  */
  void sqlite3CodeRowTrigger(
    Parse *pParse,       /* Parse context */
    Trigger *pTrigger,   /* List of triggers on table pTab */
    int op,              /* One of TK_UPDATE, TK_INSERT, TK_DELETE */
    ExprList *pChanges,  /* Changes list for any UPDATE OF triggers */
    int tr_tm,           /* One of TRIGGER_BEFORE, TRIGGER_AFTER */
    Table *pTab,         /* The table to code triggers from */
    int reg,             /* The first in an array of registers (see above) */
    int orconf,          /* ON CONFLICT policy */
    int ignoreJump       /* Instruction to jump to for RAISE(IGNORE) */
  ){
    Trigger *p;          /* Used to iterate through pTrigger list */
  
    assert( op==TK_UPDATE || op==TK_INSERT || op==TK_DELETE );
    assert( tr_tm==TRIGGER_BEFORE || tr_tm==TRIGGER_AFTER );
    assert( (op==TK_UPDATE)==(pChanges!=0) );
  
    for(p=pTrigger; p; p=p->pNext){
  
      /* Sanity checking:  The schema for the trigger and for the table are
      ** always defined.  The trigger must be in the same schema as the table
      ** or else it must be a TEMP trigger. */
      assert( p->pSchema!=0 );
      assert( p->pTabSchema!=0 );
      assert( p->pSchema==p->pTabSchema 
           || p->pSchema==pParse->db->aDb[1].pSchema );
  
      /* Determine whether we should code this trigger.  One of two choices:
      **   1. The trigger is an exact match to the current DML statement
      **   2. This is a RETURNING trigger for INSERT but we are currently
      **      doing the UPDATE part of an UPSERT.
      */
      if( (p->op==op || (p->bReturning && p->op==TK_INSERT && op==TK_UPDATE))
       && p->tr_tm==tr_tm 
       && checkColumnOverlap(p->pColumns, pChanges)
      ){
        if( !p->bReturning ){
          sqlite3CodeRowTriggerDirect(pParse, p, pTab, reg, orconf, ignoreJump);
        }else if( sqlite3IsToplevel(pParse) ){
          codeReturningTrigger(pParse, p, pTab, reg);
        }
      }
    }
  }
  
  /*
  ** Triggers may access values stored in the old.* or new.* pseudo-table. 
  ** This function returns a 32-bit bitmask indicating which columns of the 
  ** old.* or new.* tables actually are used by triggers. This information 
  ** may be used by the caller, for example, to avoid having to load the entire
  ** old.* record into memory when executing an UPDATE or DELETE command.
  **
  ** Bit 0 of the returned mask is set if the left-most column of the
  ** table may be accessed using an [old|new].<col> reference. Bit 1 is set if
  ** the second leftmost column value is required, and so on. If there
  ** are more than 32 columns in the table, and at least one of the columns
  ** with an index greater than 32 may be accessed, 0xffffffff is returned.
  **
  ** It is not possible to determine if the old.rowid or new.rowid column is 
  ** accessed by triggers. The caller must always assume that it is.
  **
  ** Parameter isNew must be either 1 or 0. If it is 0, then the mask returned
  ** applies to the old.* table. If 1, the new.* table.
  **
  ** Parameter tr_tm must be a mask with one or both of the TRIGGER_BEFORE
  ** and TRIGGER_AFTER bits set. Values accessed by BEFORE triggers are only
  ** included in the returned mask if the TRIGGER_BEFORE bit is set in the
  ** tr_tm parameter. Similarly, values accessed by AFTER triggers are only
  ** included in the returned mask if the TRIGGER_AFTER bit is set in tr_tm.
  */
  u32 sqlite3TriggerColmask(
    Parse *pParse,       /* Parse context */
    Trigger *pTrigger,   /* List of triggers on table pTab */
    ExprList *pChanges,  /* Changes list for any UPDATE OF triggers */
    int isNew,           /* 1 for new.* ref mask, 0 for old.* ref mask */
    int tr_tm,           /* Mask of TRIGGER_BEFORE|TRIGGER_AFTER */
    Table *pTab,         /* The table to code triggers from */
    int orconf           /* Default ON CONFLICT policy for trigger steps */
  ){
    const int op = pChanges ? TK_UPDATE : TK_DELETE;
    u32 mask = 0;
    Trigger *p;
  
    assert( isNew==1 || isNew==0 );
    for(p=pTrigger; p; p=p->pNext){
      if( p->op==op
       && (tr_tm&p->tr_tm)
       && checkColumnOverlap(p->pColumns,pChanges)
      ){
        if( p->bReturning ){
          mask = 0xffffffff;
        }else{
          TriggerPrg *pPrg;
          pPrg = getRowTrigger(pParse, p, pTab, orconf);
          if( pPrg ){
            mask |= pPrg->aColmask[isNew];
          }
        }
      }
    }
  
    return mask;
  }
  
  #endif /* !defined(SQLITE_OMIT_TRIGGER) */
  