text: /*-------------------------------------------------------------------------
   *
   * var.c
   *	  Var node manipulation routines
   *
   * Note: for most purposes, PlaceHolderVar is considered a Var too,
   * even if its contained expression is variable-free.  Also, CurrentOfExpr
   * is treated as a Var for purposes of determining whether an expression
   * contains variables.
   *
   *
   * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/optimizer/util/var.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "access/sysattr.h"
  #include "nodes/nodeFuncs.h"
  #include "optimizer/prep.h"
  #include "optimizer/var.h"
  #include "parser/parsetree.h"
  #include "rewrite/rewriteManip.h"
  
  
  typedef struct
  {
  	Relids		varnos;
  	int			sublevels_up;
  } pull_varnos_context;
  
  typedef struct
  {
  	Bitmapset  *varattnos;
  	Index		varno;
  } pull_varattnos_context;
  
  typedef struct
  {
  	List	   *vars;
  	int			sublevels_up;
  } pull_vars_context;
  
  typedef struct
  {
  	int			var_location;
  	int			sublevels_up;
  } locate_var_of_level_context;
  
  typedef struct
  {
  	List	   *varlist;
  	int			flags;
  } pull_var_clause_context;
  
  typedef struct
  {
  	PlannerInfo *root;
  	int			sublevels_up;
  	bool		possible_sublink;	/* could aliases include a SubLink? */
  	bool		inserted_sublink;	/* have we inserted a SubLink? */
  } flatten_join_alias_vars_context;
  
  static bool pull_varnos_walker(Node *node,
  				   pull_varnos_context *context);
  static bool pull_varattnos_walker(Node *node, pull_varattnos_context *context);
  static bool pull_vars_walker(Node *node, pull_vars_context *context);
  static bool contain_var_clause_walker(Node *node, void *context);
  static bool contain_vars_of_level_walker(Node *node, int *sublevels_up);
  static bool locate_var_of_level_walker(Node *node,
  						   locate_var_of_level_context *context);
  static bool pull_var_clause_walker(Node *node,
  					   pull_var_clause_context *context);
  static Node *flatten_join_alias_vars_mutator(Node *node,
  								flatten_join_alias_vars_context *context);
  static Relids alias_relid_set(PlannerInfo *root, Relids relids);
  
  
  /*
   * pull_varnos
   *		Create a set of all the distinct varnos present in a parsetree.
   *		Only varnos that reference level-zero rtable entries are considered.
   *
   * NOTE: this is used on not-yet-planned expressions.  It may therefore find
   * bare SubLinks, and if so it needs to recurse into them to look for uplevel
   * references to the desired rtable level!	But when we find a completed
   * SubPlan, we only need to look at the parameters passed to the subplan.
   */
  Relids
  pull_varnos(Node *node)
  {
  	pull_varnos_context context;
  
  	context.varnos = NULL;
  	context.sublevels_up = 0; // 本层的 Var
  
  	/*
  	 * Must be prepared to start with a Query or a bare expression tree; if
  	 * it's a Query, we don't want to increment sublevels_up.
  	 */
  	query_or_expression_tree_walker(node,
  									pull_varnos_walker,
  									(void *) &context,
  									0);
  
  	return context.varnos;
  }
  
  /*
   * pull_varnos_of_level
   *		Create a set of all the distinct varnos present in a parsetree.
   *		Only Vars of the specified level are considered.
   */
  Relids
  pull_varnos_of_level(Node *node, int levelsup)
  {
  	pull_varnos_context context;
  
  	context.varnos = NULL;
  	context.sublevels_up = levelsup;
  
  	/*
  	 * Must be prepared to start with a Query or a bare expression tree; if
  	 * it's a Query, we don't want to increment sublevels_up.
  	 */
  	query_or_expression_tree_walker(node,
  									pull_varnos_walker,
  									(void *) &context,
  									0);
  
  	return context.varnos;
  }
  
  static bool
  pull_varnos_walker(Node *node, pull_varnos_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  
  		if (var->varlevelsup == context->sublevels_up)
  			context->varnos = bms_add_member(context->varnos, var->varno);
  		return false;
  	}
  	if (IsA(node, CurrentOfExpr))
  	{
  		CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
  
  		if (context->sublevels_up == 0)
  			context->varnos = bms_add_member(context->varnos, cexpr->cvarno);
  		return false;
  	}
  	if (IsA(node, PlaceHolderVar))
  	{
  		/*
  		 * A PlaceHolderVar acts as a variable of its syntactic scope, or
  		 * lower than that if it references only a subset of the rels in its
  		 * syntactic scope.  It might also contain lateral references, but we
  		 * should ignore such references when computing the set of varnos in
  		 * an expression tree.  Also, if the PHV contains no variables within
  		 * its syntactic scope, it will be forced to be evaluated exactly at
  		 * the syntactic scope, so take that as the relid set.
  		 */
  		PlaceHolderVar *phv = (PlaceHolderVar *) node;
  		pull_varnos_context subcontext;
  
  		subcontext.varnos = NULL;
  		subcontext.sublevels_up = context->sublevels_up;
  		(void) pull_varnos_walker((Node *) phv->phexpr, &subcontext);
  		if (phv->phlevelsup == context->sublevels_up)
  		{
  			subcontext.varnos = bms_int_members(subcontext.varnos,
  												phv->phrels);
  			if (bms_is_empty(subcontext.varnos))
  				context->varnos = bms_add_members(context->varnos,
  												  phv->phrels);
  		}
  		context->varnos = bms_join(context->varnos, subcontext.varnos);
  		return false;
  	}
  	if (IsA(node, Query))
  	{
  		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
  		bool		result;
  
  		context->sublevels_up++;
  		result = query_tree_walker((Query *) node, pull_varnos_walker,
  								   (void *) context, 0);
  		context->sublevels_up--;
  		return result;
  	}
  	return expression_tree_walker(node, pull_varnos_walker,
  								  (void *) context);
  }
  
  
  /*
   * pull_varattnos
   *		Find all the distinct attribute numbers present in an expression tree,
   *		and add them to the initial contents of *varattnos.
   *		Only Vars of the given varno and rtable level zero are considered.
   *
   * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
   * we can include system attributes (e.g., OID) in the bitmap representation.
   *
   * Currently, this does not support unplanned subqueries; that is not needed
   * for current uses.  It will handle already-planned SubPlan nodes, though,
   * looking into only the "testexpr" and the "args" list.  (The subplan cannot
   * contain any other references to Vars of the current level.)
   */
  void
  pull_varattnos(Node *node, Index varno, Bitmapset **varattnos)
  {
  	pull_varattnos_context context;
  
  	context.varattnos = *varattnos;
  	context.varno = varno;
  
  	(void) pull_varattnos_walker(node, &context);
  
  	*varattnos = context.varattnos;
  }
  
  static bool
  pull_varattnos_walker(Node *node, pull_varattnos_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  
  		if (var->varno == context->varno && var->varlevelsup == 0)
  			context->varattnos =
  				bms_add_member(context->varattnos,
  							   var->varattno - FirstLowInvalidHeapAttributeNumber);
  		return false;
  	}
  
  	/* Should not find an unplanned subquery */
  	Assert(!IsA(node, Query));
  
  	return expression_tree_walker(node, pull_varattnos_walker,
  								  (void *) context);
  }
  
  
  /*
   * pull_vars_of_level
   *		Create a list of all Vars (and PlaceHolderVars) referencing the
   *		specified query level in the given parsetree.
   *
   * Caution: the Vars are not copied, only linked into the list.
   */
  List *
  pull_vars_of_level(Node *node, int levelsup)
  {
  	pull_vars_context context;
  
  	context.vars = NIL;
  	context.sublevels_up = levelsup;
  
  	/*
  	 * Must be prepared to start with a Query or a bare expression tree; if
  	 * it's a Query, we don't want to increment sublevels_up.
  	 */
  	query_or_expression_tree_walker(node,
  									pull_vars_walker,
  									(void *) &context,
  									0);
  
  	return context.vars;
  }
  
  static bool
  pull_vars_walker(Node *node, pull_vars_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  
  		if (var->varlevelsup == context->sublevels_up)
  			context->vars = lappend(context->vars, var);
  		return false;
  	}
  	if (IsA(node, PlaceHolderVar))
  	{
  		PlaceHolderVar *phv = (PlaceHolderVar *) node;
  
  		if (phv->phlevelsup == context->sublevels_up)
  			context->vars = lappend(context->vars, phv);
  		/* we don't want to look into the contained expression */
  		return false;
  	}
  	if (IsA(node, Query))
  	{
  		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
  		bool		result;
  
  		context->sublevels_up++;
  		result = query_tree_walker((Query *) node, pull_vars_walker,
  								   (void *) context, 0);
  		context->sublevels_up--;
  		return result;
  	}
  	return expression_tree_walker(node, pull_vars_walker,
  								  (void *) context);
  }
  
  
  /*
   * contain_var_clause
   *	  Recursively scan a clause to discover whether it contains any Var nodes
   *	  (of the current query level).
   *
   *	  Returns true if any varnode found.
   *
   * Does not examine subqueries, therefore must only be used after reduction
   * of sublinks to subplans!
   */
  bool
  contain_var_clause(Node *node)
  {
  	return contain_var_clause_walker(node, NULL);
  }
  
  static bool
  contain_var_clause_walker(Node *node, void *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		if (((Var *) node)->varlevelsup == 0)
  			return true;		/* abort the tree traversal and return true */
  		return false;
  	}
  	if (IsA(node, CurrentOfExpr))
  		return true;
  	if (IsA(node, PlaceHolderVar))
  	{
  		if (((PlaceHolderVar *) node)->phlevelsup == 0)
  			return true;		/* abort the tree traversal and return true */
  		/* else fall through to check the contained expr */
  	}
  	return expression_tree_walker(node, contain_var_clause_walker, context);
  }
  
  
  /*
   * contain_vars_of_level
   *	  Recursively scan a clause to discover whether it contains any Var nodes
   *	  of the specified query level.
   *
   *	  Returns true if any such Var found.
   *
   * Will recurse into sublinks.  Also, may be invoked directly on a Query.
   */
  bool
  contain_vars_of_level(Node *node, int levelsup)
  {
  	int			sublevels_up = levelsup;
  
  	return query_or_expression_tree_walker(node,
  										   contain_vars_of_level_walker,
  										   (void *) &sublevels_up,
  										   0);
  }
  
  static bool
  contain_vars_of_level_walker(Node *node, int *sublevels_up)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		if (((Var *) node)->varlevelsup == *sublevels_up)
  			return true;		/* abort tree traversal and return true */
  		return false;
  	}
  	if (IsA(node, CurrentOfExpr))
  	{
  		if (*sublevels_up == 0)
  			return true;
  		return false;
  	}
  	if (IsA(node, PlaceHolderVar))
  	{
  		if (((PlaceHolderVar *) node)->phlevelsup == *sublevels_up)
  			return true;		/* abort the tree traversal and return true */
  		/* else fall through to check the contained expr */
  	}
  	if (IsA(node, Query))
  	{
  		/* Recurse into subselects */
  		bool		result;
  
  		(*sublevels_up)++;
  		result = query_tree_walker((Query *) node,
  								   contain_vars_of_level_walker,
  								   (void *) sublevels_up,
  								   0);
  		(*sublevels_up)--;
  		return result;
  	}
  	return expression_tree_walker(node,
  								  contain_vars_of_level_walker,
  								  (void *) sublevels_up);
  }
  
  
  /*
   * locate_var_of_level
   *	  Find the parse location of any Var of the specified query level.
   *
   * Returns -1 if no such Var is in the querytree, or if they all have
   * unknown parse location.  (The former case is probably caller error,
   * but we don't bother to distinguish it from the latter case.)
   *
   * Will recurse into sublinks.  Also, may be invoked directly on a Query.
   *
   * Note: it might seem appropriate to merge this functionality into
   * contain_vars_of_level, but that would complicate that function's API.
   * Currently, the only uses of this function are for error reporting,
   * and so shaving cycles probably isn't very important.
   */
  int
  locate_var_of_level(Node *node, int levelsup)
  {
  	locate_var_of_level_context context;
  
  	context.var_location = -1;	/* in case we find nothing */
  	context.sublevels_up = levelsup;
  
  	(void) query_or_expression_tree_walker(node,
  										   locate_var_of_level_walker,
  										   (void *) &context,
  										   0);
  
  	return context.var_location;
  }
  
  static bool
  locate_var_of_level_walker(Node *node,
  						   locate_var_of_level_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  
  		if (var->varlevelsup == context->sublevels_up &&
  			var->location >= 0)
  		{
  			context->var_location = var->location;
  			return true;		/* abort tree traversal and return true */
  		}
  		return false;
  	}
  	if (IsA(node, CurrentOfExpr))
  	{
  		/* since CurrentOfExpr doesn't carry location, nothing we can do */
  		return false;
  	}
  	/* No extra code needed for PlaceHolderVar; just look in contained expr */
  	if (IsA(node, Query))
  	{
  		/* Recurse into subselects */
  		bool		result;
  
  		context->sublevels_up++;
  		result = query_tree_walker((Query *) node,
  								   locate_var_of_level_walker,
  								   (void *) context,
  								   0);
  		context->sublevels_up--;
  		return result;
  	}
  	return expression_tree_walker(node,
  								  locate_var_of_level_walker,
  								  (void *) context);
  }
  
  
  /*
   * pull_var_clause
   *	  Recursively pulls all Var nodes from an expression clause.
   *
   *	  Aggrefs are handled according to these bits in 'flags':
   *		PVC_INCLUDE_AGGREGATES		include Aggrefs in output list
   *		PVC_RECURSE_AGGREGATES		recurse into Aggref arguments
   *		neither flag				throw error if Aggref found
   *	  Vars within an Aggref's expression are included in the result only
   *	  when PVC_RECURSE_AGGREGATES is specified.
   *
   *	  WindowFuncs are handled according to these bits in 'flags':
   *		PVC_INCLUDE_WINDOWFUNCS		include WindowFuncs in output list
   *		PVC_RECURSE_WINDOWFUNCS		recurse into WindowFunc arguments
   *		neither flag				throw error if WindowFunc found
   *	  Vars within a WindowFunc's expression are included in the result only
   *	  when PVC_RECURSE_WINDOWFUNCS is specified.
   *
   *	  PlaceHolderVars are handled according to these bits in 'flags':
   *		PVC_INCLUDE_PLACEHOLDERS	include PlaceHolderVars in output list
   *		PVC_RECURSE_PLACEHOLDERS	recurse into PlaceHolderVar arguments
   *		neither flag				throw error if PlaceHolderVar found
   *	  Vars within a PHV's expression are included in the result only
   *	  when PVC_RECURSE_PLACEHOLDERS is specified.
   *
   *	  GroupingFuncs are treated mostly like Aggrefs, and so do not need
   *	  their own flag bits.
   *
   *	  CurrentOfExpr nodes are ignored in all cases.
   *
   *	  Upper-level vars (with varlevelsup > 0) should not be seen here,
   *	  likewise for upper-level Aggrefs and PlaceHolderVars.
   *
   *	  Returns list of nodes found.  Note the nodes themselves are not
   *	  copied, only referenced.
   *
   * Does not examine subqueries, therefore must only be used after reduction
   * of sublinks to subplans!
   */
  List *
  pull_var_clause(Node *node, int flags)
  {
  	pull_var_clause_context context;
  
  	/* Assert that caller has not specified inconsistent flags */
  	Assert((flags & (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES))
  		   != (PVC_INCLUDE_AGGREGATES | PVC_RECURSE_AGGREGATES));
  	Assert((flags & (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS))
  		   != (PVC_INCLUDE_WINDOWFUNCS | PVC_RECURSE_WINDOWFUNCS));
  	Assert((flags & (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS))
  		   != (PVC_INCLUDE_PLACEHOLDERS | PVC_RECURSE_PLACEHOLDERS));
  
  	context.varlist = NIL;
  	context.flags = flags;
  
  	pull_var_clause_walker(node, &context);
  	return context.varlist;
  }
  
  static bool
  pull_var_clause_walker(Node *node, pull_var_clause_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		if (((Var *) node)->varlevelsup != 0)
  			elog(ERROR, "Upper-level Var found where not expected");
  		context->varlist = lappend(context->varlist, node);
  		return false;
  	}
  	else if (IsA(node, Aggref))
  	{
  		if (((Aggref *) node)->agglevelsup != 0)
  			elog(ERROR, "Upper-level Aggref found where not expected");
  		if (context->flags & PVC_INCLUDE_AGGREGATES)
  		{
  			context->varlist = lappend(context->varlist, node);
  			/* we do NOT descend into the contained expression */
  			return false;
  		}
  		else if (context->flags & PVC_RECURSE_AGGREGATES)
  		{
  			/* fall through to recurse into the aggregate's arguments */
  		}
  		else
  			elog(ERROR, "Aggref found where not expected");
  	}
  	else if (IsA(node, GroupingFunc))
  	{
  		if (((GroupingFunc *) node)->agglevelsup != 0)
  			elog(ERROR, "Upper-level GROUPING found where not expected");
  		if (context->flags & PVC_INCLUDE_AGGREGATES)
  		{
  			context->varlist = lappend(context->varlist, node);
  			/* we do NOT descend into the contained expression */
  			return false;
  		}
  		else if (context->flags & PVC_RECURSE_AGGREGATES)
  		{
  			/*
  			 * We do NOT descend into the contained expression, even if the
  			 * caller asked for it, because we never actually evaluate it -
  			 * the result is driven entirely off the associated GROUP BY
  			 * clause, so we never need to extract the actual Vars here.
  			 */
  			return false;
  		}
  		else
  			elog(ERROR, "GROUPING found where not expected");
  	}
  	else if (IsA(node, WindowFunc))
  	{
  		/* WindowFuncs have no levelsup field to check ... */
  		if (context->flags & PVC_INCLUDE_WINDOWFUNCS)
  		{
  			context->varlist = lappend(context->varlist, node);
  			/* we do NOT descend into the contained expressions */
  			return false;
  		}
  		else if (context->flags & PVC_RECURSE_WINDOWFUNCS)
  		{
  			/* fall through to recurse into the windowfunc's arguments */
  		}
  		else
  			elog(ERROR, "WindowFunc found where not expected");
  	}
  	else if (IsA(node, PlaceHolderVar))
  	{
  		if (((PlaceHolderVar *) node)->phlevelsup != 0)
  			elog(ERROR, "Upper-level PlaceHolderVar found where not expected");
  		if (context->flags & PVC_INCLUDE_PLACEHOLDERS)
  		{
  			context->varlist = lappend(context->varlist, node);
  			/* we do NOT descend into the contained expression */
  			return false;
  		}
  		else if (context->flags & PVC_RECURSE_PLACEHOLDERS)
  		{
  			/* fall through to recurse into the placeholder's expression */
  		}
  		else
  			elog(ERROR, "PlaceHolderVar found where not expected");
  	}
  	return expression_tree_walker(node, pull_var_clause_walker,
  								  (void *) context);
  }
  
  
  /*
   * flatten_join_alias_vars
   *	  Replace Vars that reference JOIN outputs with references to the original
   *	  relation variables instead.  This allows quals involving such vars to be
   *	  pushed down.  Whole-row Vars that reference JOIN relations are expanded
   *	  into RowExpr constructs that name the individual output Vars.  This
   *	  is necessary since we will not scan the JOIN as a base relation, which
   *	  is the only way that the executor can directly handle whole-row Vars.
   *
   * This also adjusts relid sets found in some expression node types to
   * substitute the contained base rels for any join relid.
   *
   * If a JOIN contains sub-selects that have been flattened, its join alias
   * entries might now be arbitrary expressions, not just Vars.  This affects
   * this function in one important way: we might find ourselves inserting
   * SubLink expressions into subqueries, and we must make sure that their
   * Query.hasSubLinks fields get set to TRUE if so.  If there are any
   * SubLinks in the join alias lists, the outer Query should already have
   * hasSubLinks = TRUE, so this is only relevant to un-flattened subqueries.
   *
   * NOTE: this is used on not-yet-planned expressions.  We do not expect it
   * to be applied directly to the whole Query, so if we see a Query to start
   * with, we do want to increment sublevels_up (this occurs for LATERAL
   * subqueries).
   */
  Node *
  flatten_join_alias_vars(PlannerInfo *root, Node *node)
  {
  	flatten_join_alias_vars_context context;
  
  	context.root = root;
  	context.sublevels_up = 0;
  	/* flag whether join aliases could possibly contain SubLinks */
  	context.possible_sublink = root->parse->hasSubLinks;
  	/* if hasSubLinks is already true, no need to work hard */
  	context.inserted_sublink = root->parse->hasSubLinks;
  
  	return flatten_join_alias_vars_mutator(node, &context);
  }
  
  static Node *
  flatten_join_alias_vars_mutator(Node *node,
  								flatten_join_alias_vars_context *context)
  {
  	if (node == NULL)
  		return NULL;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  		RangeTblEntry *rte;
  		Node	   *newvar;
  
  		/* No change unless Var belongs to a JOIN of the target level */
  		if (var->varlevelsup != context->sublevels_up)
  			return node;		/* no need to copy, really */
  		rte = rt_fetch(var->varno, context->root->parse->rtable);
  		if (rte->rtekind != RTE_JOIN)
  			return node;
  		if (var->varattno == InvalidAttrNumber)
  		{
  			/* Must expand whole-row reference */
  			RowExpr    *rowexpr;
  			List	   *fields = NIL;
  			List	   *colnames = NIL;
  			AttrNumber	attnum;
  			ListCell   *lv;
  			ListCell   *ln;
  
  			attnum = 0;
  			Assert(list_length(rte->joinaliasvars) == list_length(rte->eref->colnames));
  			forboth(lv, rte->joinaliasvars, ln, rte->eref->colnames)
  			{
  				newvar = (Node *) lfirst(lv);
  				attnum++;
  				/* Ignore dropped columns */
  				if (newvar == NULL)
  					continue;
  				newvar = copyObject(newvar);
  
  				/*
  				 * If we are expanding an alias carried down from an upper
  				 * query, must adjust its varlevelsup fields.
  				 */
  				if (context->sublevels_up != 0)
  					IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
  				/* Preserve original Var's location, if possible */
  				if (IsA(newvar, Var))
  					((Var *) newvar)->location = var->location;
  				/* Recurse in case join input is itself a join */
  				/* (also takes care of setting inserted_sublink if needed) */
  				newvar = flatten_join_alias_vars_mutator(newvar, context);
  				fields = lappend(fields, newvar);
  				/* We need the names of non-dropped columns, too */
  				colnames = lappend(colnames, copyObject((Node *) lfirst(ln)));
  			}
  			rowexpr = makeNode(RowExpr);
  			rowexpr->args = fields;
  			rowexpr->row_typeid = var->vartype;
  			rowexpr->row_format = COERCE_IMPLICIT_CAST;
  			rowexpr->colnames = colnames;
  			rowexpr->location = var->location;
  
  			return (Node *) rowexpr;
  		}
  
  		/* Expand join alias reference */
  		Assert(var->varattno > 0);
  		newvar = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);
  		Assert(newvar != NULL);
  		newvar = copyObject(newvar);
  
  		/*
  		 * If we are expanding an alias carried down from an upper query, must
  		 * adjust its varlevelsup fields.
  		 */
  		if (context->sublevels_up != 0)
  			IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
  
  		/* Preserve original Var's location, if possible */
  		if (IsA(newvar, Var))
  			((Var *) newvar)->location = var->location;
  
  		/* Recurse in case join input is itself a join */
  		newvar = flatten_join_alias_vars_mutator(newvar, context);
  
  		/* Detect if we are adding a sublink to query */
  		if (context->possible_sublink && !context->inserted_sublink)
  			context->inserted_sublink = checkExprHasSubLink(newvar);
  
  		return newvar;
  	}
  	if (IsA(node, PlaceHolderVar))
  	{
  		/* Copy the PlaceHolderVar node with correct mutation of subnodes */
  		PlaceHolderVar *phv;
  
  		phv = (PlaceHolderVar *) expression_tree_mutator(node,
  														 flatten_join_alias_vars_mutator,
  														 (void *) context);
  		/* now fix PlaceHolderVar's relid sets */
  		if (phv->phlevelsup == context->sublevels_up)
  		{
  			phv->phrels = alias_relid_set(context->root,
  										  phv->phrels);
  		}
  		return (Node *) phv;
  	}
  
  	if (IsA(node, Query))
  	{
  		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
  		Query	   *newnode;
  		bool		save_inserted_sublink;
  
  		context->sublevels_up++;
  		save_inserted_sublink = context->inserted_sublink;
  		context->inserted_sublink = ((Query *) node)->hasSubLinks;
  		newnode = query_tree_mutator((Query *) node,
  									 flatten_join_alias_vars_mutator,
  									 (void *) context,
  									 QTW_IGNORE_JOINALIASES);
  		newnode->hasSubLinks |= context->inserted_sublink;
  		context->inserted_sublink = save_inserted_sublink;
  		context->sublevels_up--;
  		return (Node *) newnode;
  	}
  	/* Already-planned tree not supported */
  	Assert(!IsA(node, SubPlan));
  	/* Shouldn't need to handle these planner auxiliary nodes here */
  	Assert(!IsA(node, SpecialJoinInfo));
  	Assert(!IsA(node, PlaceHolderInfo));
  	Assert(!IsA(node, MinMaxAggInfo));
  
  	return expression_tree_mutator(node, flatten_join_alias_vars_mutator,
  								   (void *) context);
  }
  
  /*
   * alias_relid_set: in a set of RT indexes, replace joins by their
   * underlying base relids
   */
  static Relids
  alias_relid_set(PlannerInfo *root, Relids relids)
  {
  	Relids		result = NULL;
  	int			rtindex;
  
  	rtindex = -1;
  	while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
  	{
  		RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);
  
  		if (rte->rtekind == RTE_JOIN)
  			result = bms_join(result, get_relids_for_join(root, rtindex));
  		else
  			result = bms_add_member(result, rtindex);
  	}
  	return result;
  }
  