text: /*-------------------------------------------------------------------------
   *
   * var.c
   *	  Var node manipulation routines
   *
   * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  $PostgreSQL: pgsql/src/backend/optimizer/util/var.c,v 1.68.2.1 2010/07/08 00:14:22 tgl Exp $
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include "optimizer/clauses.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
  {
  	int			varno;
  	int			varattno;
  	int			sublevels_up;
  } contain_var_reference_context;
  
  typedef struct
  {
  	int			min_varlevel;
  	int			sublevels_up;
  } find_minimum_var_level_context;
  
  typedef struct
  {
  	List	   *varlist;
  	bool		includeUpperVars;
  } 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 contain_var_reference_walker(Node *node,
  							 contain_var_reference_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 contain_vars_above_level_walker(Node *node, int *sublevels_up);
  static bool find_minimum_var_level_walker(Node *node,
  							  find_minimum_var_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;
  
  	/*
  	 * 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, 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);
  }
  
  
  /*
   *		contain_var_reference
   *
   *		Detect whether a parsetree contains any references to a specified
   *		attribute of a specified rtable entry.
   *
   * 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 entry!	But when we find a completed
   * SubPlan, we only need to look at the parameters passed to the subplan.
   */
  bool
  contain_var_reference(Node *node, int varno, int varattno, int levelsup)
  {
  	contain_var_reference_context context;
  
  	context.varno = varno;
  	context.varattno = varattno;
  	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.
  	 */
  	return query_or_expression_tree_walker(node,
  										   contain_var_reference_walker,
  										   (void *) &context,
  										   0);
  }
  
  static bool
  contain_var_reference_walker(Node *node,
  							 contain_var_reference_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		Var		   *var = (Var *) node;
  
  		if (var->varno == context->varno &&
  			var->varattno == context->varattno &&
  			var->varlevelsup == context->sublevels_up)
  			return true;
  		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,
  								   contain_var_reference_walker,
  								   (void *) context, 0);
  		context->sublevels_up--;
  		return result;
  	}
  	return expression_tree_walker(node, contain_var_reference_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;
  	}
  	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 */
  	}
  	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);
  }
  
  /*
   * contain_vars_above_level
   *	  Recursively scan a clause to discover whether it contains any Var nodes
   *	  above the specified query level.	(For example, pass zero to detect
   *	  all nonlocal Vars.)
   *
   *	  Returns true if any such Var found.
   *
   * Will recurse into sublinks.	Also, may be invoked directly on a Query.
   */
  bool
  contain_vars_above_level(Node *node, int levelsup)
  {
  	int			sublevels_up = levelsup;
  
  	return query_or_expression_tree_walker(node,
  										   contain_vars_above_level_walker,
  										   (void *) &sublevels_up,
  										   0);
  }
  
  static bool
  contain_vars_above_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 */
  	}
  	if (IsA(node, Query))
  	{
  		/* Recurse into subselects */
  		bool		result;
  
  		(*sublevels_up)++;
  		result = query_tree_walker((Query *) node,
  								   contain_vars_above_level_walker,
  								   (void *) sublevels_up,
  								   0);
  		(*sublevels_up)--;
  		return result;
  	}
  	return expression_tree_walker(node,
  								  contain_vars_above_level_walker,
  								  (void *) sublevels_up);
  }
  
  
  /*
   * find_minimum_var_level
   *	  Recursively scan a clause to find the lowest variable level it
   *	  contains --- for example, zero is returned if there are any local
   *	  variables, one if there are no local variables but there are
   *	  one-level-up outer references, etc.  Subqueries are scanned to see
   *	  if they possess relevant outer references.  (But any local variables
   *	  within subqueries are not relevant.)
   *
   *	  -1 is returned if the clause has no variables at all.
   *
   * Will recurse into sublinks.	Also, may be invoked directly on a Query.
   */
  int
  find_minimum_var_level(Node *node)
  {
  	find_minimum_var_level_context context;
  
  	context.min_varlevel = -1;	/* signifies nothing found yet */
  	context.sublevels_up = 0;
  
  	(void) query_or_expression_tree_walker(node,
  										   find_minimum_var_level_walker,
  										   (void *) &context,
  										   0);
  
  	return context.min_varlevel;
  }
  
  static bool
  find_minimum_var_level_walker(Node *node,
  							  find_minimum_var_level_context *context)
  {
  	if (node == NULL)
  		return false;
  	if (IsA(node, Var))
  	{
  		int			varlevelsup = ((Var *) node)->varlevelsup;
  
  		/* convert levelsup to frame of reference of original query */
  		varlevelsup -= context->sublevels_up;
  		/* ignore local vars of subqueries */
  		if (varlevelsup >= 0)
  		{
  			if (context->min_varlevel < 0 ||
  				context->min_varlevel > varlevelsup)
  			{
  				context->min_varlevel = varlevelsup;
  
  				/*
  				 * As soon as we find a local variable, we can abort the tree
  				 * traversal, since min_varlevel is then certainly 0.
  				 */
  				if (varlevelsup == 0)
  					return true;
  			}
  		}
  	}
  
  	/*
  	 * An Aggref must be treated like a Var of its level.  Normally we'd get
  	 * the same result from looking at the Vars in the aggregate's argument,
  	 * but this fails in the case of a Var-less aggregate call (COUNT(*)).
  	 */
  	if (IsA(node, Aggref))
  	{
  		int			agglevelsup = ((Aggref *) node)->agglevelsup;
  
  		/* convert levelsup to frame of reference of original query */
  		agglevelsup -= context->sublevels_up;
  		/* ignore local aggs of subqueries */
  		if (agglevelsup >= 0)
  		{
  			if (context->min_varlevel < 0 ||
  				context->min_varlevel > agglevelsup)
  			{
  				context->min_varlevel = agglevelsup;
  
  				/*
  				 * As soon as we find a local aggregate, we can abort the tree
  				 * traversal, since min_varlevel is then certainly 0.
  				 */
  				if (agglevelsup == 0)
  					return true;
  			}
  		}
  	}
  	if (IsA(node, Query))
  	{
  		/* Recurse into subselects */
  		bool		result;
  
  		context->sublevels_up++;
  		result = query_tree_walker((Query *) node,
  								   find_minimum_var_level_walker,
  								   (void *) context,
  								   0);
  		context->sublevels_up--;
  		return result;
  	}
  	return expression_tree_walker(node,
  								  find_minimum_var_level_walker,
  								  (void *) context);
  }
  
  
  /*
   * pull_var_clause
   *	  Recursively pulls all var nodes from an expression clause.
   *
   *	  Upper-level vars (with varlevelsup > 0) are included only
   *	  if includeUpperVars is true.	Most callers probably want
   *	  to ignore upper-level vars.
   *
   *	  Returns list of varnodes found.  Note the varnodes 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, bool includeUpperVars)
  {
  	pull_var_clause_context context;
  
  	context.varlist = NIL;
  	context.includeUpperVars = includeUpperVars;
  
  	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 || context->includeUpperVars)
  			context->varlist = lappend(context->varlist, node);
  		return false;
  	}
  	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.
   *
   * 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 a Query node.
   */
  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;
  			AttrNumber	attnum;
  			ListCell   *l;
  
  			attnum = 0;
  			foreach(l, rte->joinaliasvars)
  			{
  				newvar = (Node *) lfirst(l);
  				attnum++;
  				/* Ignore dropped columns */
  				if (IsA(newvar, Const))
  					continue;
  
  				/*
  				 * If we are expanding an alias carried down from an upper
  				 * query, must adjust its varlevelsup fields.
  				 */
  				if (context->sublevels_up != 0)
  				{
  					newvar = copyObject(newvar);
  					IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
  				}
  				/* 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);
  			}
  			rowexpr = makeNode(RowExpr);
  			rowexpr->args = fields;
  			rowexpr->row_typeid = var->vartype;
  			rowexpr->row_format = COERCE_IMPLICIT_CAST;
  
  			return (Node *) rowexpr;
  		}
  
  		/* Expand join alias reference */
  		Assert(var->varattno > 0);
  		newvar = (Node *) list_nth(rte->joinaliasvars, var->varattno - 1);
  
  		/*
  		 * If we are expanding an alias carried down from an upper query, must
  		 * adjust its varlevelsup fields.
  		 */
  		if (context->sublevels_up != 0)
  		{
  			newvar = copyObject(newvar);
  			IncrementVarSublevelsUp(newvar, context->sublevels_up, 0);
  		}
  
  		/* 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, InClauseInfo))
  	{
  		/* Copy the InClauseInfo node with correct mutation of subnodes */
  		InClauseInfo *ininfo;
  
  		ininfo = (InClauseInfo *) expression_tree_mutator(node,
  											 flatten_join_alias_vars_mutator,
  														  (void *) context);
  		/* now fix InClauseInfo's relid sets */
  		if (context->sublevels_up == 0)
  		{
  			ininfo->lefthand = alias_relid_set(context->root,
  											   ininfo->lefthand);
  			ininfo->righthand = alias_relid_set(context->root,
  												ininfo->righthand);
  		}
  		return (Node *) ininfo;
  	}
  
  	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(!is_subplan(node));
  
  	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;
  	Relids		tmprelids;
  	int			rtindex;
  
  	tmprelids = bms_copy(relids);
  	while ((rtindex = bms_first_member(tmprelids)) >= 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);
  	}
  	bms_free(tmprelids);
  	return result;
  }
  