var.c

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/*-------------------------------------------------------------------------
 *
 * var.c
 *	  Var node manipulation routines
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/util/var.c,v 1.73 2008/01/01 19:45:50 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup.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;
} flatten_join_alias_vars_context;

static bool pull_varnos_walker(Node *node,
				   pull_varnos_context *context);
static bool pull_varattnos_walker(Node *node, Bitmapset **varattnos);
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, CurrentOfExpr))
	{
		CurrentOfExpr *cexpr = (CurrentOfExpr *) node;

		if (context->sublevels_up == 0)
			context->varnos = bms_add_member(context->varnos, cexpr->cvarno);
		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 that reference RTE 1 of 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 subqueries nor expressions containing
 * references to multiple tables; not needed since it's only applied to
 * index expressions and predicates.
 */
void
pull_varattnos(Node *node, Bitmapset **varattnos)
{
	(void) pull_varattnos_walker(node, varattnos);
}

static bool
pull_varattnos_walker(Node *node, Bitmapset **varattnos)
{
	if (node == NULL)
		return false;
	if (IsA(node, Var))
	{
		Var		   *var = (Var *) node;

		Assert(var->varno == 1);
		*varattnos = bms_add_member(*varattnos,
						 var->varattno - FirstLowInvalidHeapAttributeNumber);
		return false;
	}
	/* Should not find a subquery or subplan */
	Assert(!IsA(node, Query));
	Assert(!is_subplan(node));

	return expression_tree_walker(node, pull_varattnos_walker,
								  (void *) varattnos);
}


/*
 *		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;
	}
	if (IsA(node, CurrentOfExpr))
		return true;
	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, 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)