path: root/src/backend/optimizer/plan/subselect.c

/*-------------------------------------------------------------------------
 *
 * subselect.c
 *	  Planning routines for subselects and parameters.
 *
 * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/subselect.c,v 1.126 2007/11/15 21:14:36 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/subselect.h"
#include "optimizer/var.h"
#include "parser/parse_expr.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


typedef struct convert_testexpr_context
{
	PlannerInfo *root;
	int			rtindex;		/* RT index for Vars, or 0 for Params */
	List	   *righthandIds;	/* accumulated list of Vars or Param IDs */
} convert_testexpr_context;

typedef struct process_sublinks_context
{
	PlannerInfo *root;
	bool		isTopQual;
}	process_sublinks_context;

typedef struct finalize_primnode_context
{
	PlannerInfo *root;
	Bitmapset  *paramids;		/* Set of PARAM_EXEC paramids found */
	Bitmapset  *outer_params;	/* Set of accessible outer paramids */
} finalize_primnode_context;


static Node *convert_testexpr(PlannerInfo *root,
				 Node *testexpr,
				 int rtindex,
				 List **righthandIds);
static Node *convert_testexpr_mutator(Node *node,
						 convert_testexpr_context *context);
static bool subplan_is_hashable(SubLink *slink, SubPlan *node, Plan *plan);
static bool hash_ok_operator(OpExpr *expr);
static Node *replace_correlation_vars_mutator(Node *node, PlannerInfo *root);
static Node *process_sublinks_mutator(Node *node,
						 process_sublinks_context * context);
static Bitmapset *finalize_plan(PlannerInfo *root,
			  Plan *plan,
			  Bitmapset *outer_params,
			  Bitmapset *valid_params);
static bool finalize_primnode(Node *node, finalize_primnode_context *context);


/*
 * Generate a Param node to replace the given Var,
 * which is expected to have varlevelsup > 0 (ie, it is not local).
 */
static Param *
replace_outer_var(PlannerInfo *root, Var *var)
{
	Param	   *retval;
	ListCell   *ppl;
	PlannerParamItem *pitem;
	Index		abslevel;
	int			i;

	Assert(var->varlevelsup > 0 && var->varlevelsup < root->query_level);
	abslevel = root->query_level - var->varlevelsup;

	/*
	 * If there's already a paramlist entry for this same Var, just use it.
	 * NOTE: in sufficiently complex querytrees, it is possible for the same
	 * varno/abslevel to refer to different RTEs in different parts of the
	 * parsetree, so that different fields might end up sharing the same Param
	 * number.	As long as we check the vartype as well, I believe that this
	 * sort of aliasing will cause no trouble. The correct field should get
	 * stored into the Param slot at execution in each part of the tree.
	 *
	 * We also need to demand a match on vartypmod.  This does not matter for
	 * the Param itself, since those are not typmod-dependent, but it does
	 * matter when make_subplan() instantiates a modified copy of the Var for
	 * a subplan's args list.
	 */
	i = 0;
	foreach(ppl, root->glob->paramlist)
	{
		pitem = (PlannerParamItem *) lfirst(ppl);
		if (pitem->abslevel == abslevel && IsA(pitem->item, Var))
		{
			Var		   *pvar = (Var *) pitem->item;

			if (pvar->varno == var->varno &&
				pvar->varattno == var->varattno &&
				pvar->vartype == var->vartype &&
				pvar->vartypmod == var->vartypmod)
				break;
		}
		i++;
	}

	if (!ppl)
	{
		/* Nope, so make a new one */
		var = (Var *) copyObject(var);
		var->varlevelsup = 0;

		pitem = makeNode(PlannerParamItem);
		pitem->item = (Node *) var;
		pitem->abslevel = abslevel;

		root->glob->paramlist = lappend(root->glob->paramlist, pitem);
		/* i is already the correct index for the new item */
	}

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = i;
	retval->paramtype = var->vartype;
	retval->paramtypmod = var->vartypmod;

	return retval;
}

/*
 * Generate a Param node to replace the given Aggref
 * which is expected to have agglevelsup > 0 (ie, it is not local).
 */
static Param *
replace_outer_agg(PlannerInfo *root, Aggref *agg)
{
	Param	   *retval;
	PlannerParamItem *pitem;
	Index		abslevel;
	int			i;

	Assert(agg->agglevelsup > 0 && agg->agglevelsup < root->query_level);
	abslevel = root->query_level - agg->agglevelsup;

	/*
	 * It does not seem worthwhile to try to match duplicate outer aggs. Just
	 * make a new slot every time.
	 */
	agg = (Aggref *) copyObject(agg);
	IncrementVarSublevelsUp((Node *) agg, -((int) agg->agglevelsup), 0);
	Assert(agg->agglevelsup == 0);

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) agg;
	pitem->abslevel = abslevel;

	root->glob->paramlist = lappend(root->glob->paramlist, pitem);
	i = list_length(root->glob->paramlist) - 1;

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = i;
	retval->paramtype = agg->aggtype;
	retval->paramtypmod = -1;

	return retval;
}

/*
 * Generate a new Param node that will not conflict with any other.
 *
 * This is used to allocate PARAM_EXEC slots for subplan outputs.
 */
static Param *
generate_new_param(PlannerInfo *root, Oid paramtype, int32 paramtypmod)
{
	Param	   *retval;
	PlannerParamItem *pitem;

	retval = makeNode(Param);
	retval->paramkind = PARAM_EXEC;
	retval->paramid = list_length(root->glob->paramlist);
	retval->paramtype = paramtype;
	retval->paramtypmod = paramtypmod;

	pitem = makeNode(PlannerParamItem);
	pitem->item = (Node *) retval;
	pitem->abslevel = root->query_level;

	root->glob->paramlist = lappend(root->glob->paramlist, pitem);

	return retval;
}

/*
 * Get the datatype of the first column of the plan's output.
 *
 * This is stored for ARRAY_SUBLINK and for exprType(), which doesn't have any
 * way to get at the plan associated with a SubPlan node.  We really only need
 * the value for EXPR_SUBLINK and ARRAY_SUBLINK subplans, but for consistency
 * we set it always.
 */
static Oid
get_first_col_type(Plan *plan)
{
	TargetEntry *tent = (TargetEntry *) linitial(plan->targetlist);

	Assert(IsA(tent, TargetEntry));
	Assert(!tent->resjunk);
	return exprType((Node *) tent->expr);
}

/*
 * Convert a SubLink (as created by the parser) into a SubPlan.
 *
 * We are given the original SubLink and the already-processed testexpr
 * (use this instead of the SubLink's own field).  We are also told if
 * this expression appears at top level of a WHERE/HAVING qual.
 *
 * The result is whatever we need to substitute in place of the SubLink
 * node in the executable expression.  This will be either the SubPlan
 * node (if we have to do the subplan as a subplan), or a Param node
 * representing the result of an InitPlan, or a row comparison expression
 * tree containing InitPlan Param nodes.
 */
static Node *
make_subplan(PlannerInfo *root, SubLink *slink, Node *testexpr, bool isTopQual)
{
	Query	   *subquery = (Query *) (slink->subselect);
	double		tuple_fraction;
	SubPlan    *splan;
	Plan	   *plan;
	PlannerInfo *subroot;
	bool		isInitPlan;
	Bitmapset  *tmpset;
	int			paramid;
	Node	   *result;

	/*
	 * Copy the source Query node.	This is a quick and dirty kluge to resolve
	 * the fact that the parser can generate trees with multiple links to the
	 * same sub-Query node, but the planner wants to scribble on the Query.
	 * Try to clean this up when we do querytree redesign...
	 */
	subquery = (Query *) copyObject(subquery);

	/*
	 * For an EXISTS subplan, tell lower-level planner to expect that only the
	 * first tuple will be retrieved.  For ALL and ANY subplans, we will be
	 * able to stop evaluating if the test condition fails, so very often not
	 * all the tuples will be retrieved; for lack of a better idea, specify
	 * 50% retrieval.  For EXPR and ROWCOMPARE subplans, use default behavior
	 * (we're only expecting one row out, anyway).
	 *
	 * NOTE: if you change these numbers, also change cost_qual_eval_walker()
	 * and get_initplan_cost() in path/costsize.c.
	 *
	 * XXX If an ALL/ANY subplan is uncorrelated, we may decide to hash or
	 * materialize its result below.  In that case it would've been better to
	 * specify full retrieval.	At present, however, we can only detect
	 * correlation or lack of it after we've made the subplan :-(. Perhaps
	 * detection of correlation should be done as a separate step. Meanwhile,
	 * we don't want to be too optimistic about the percentage of tuples
	 * retrieved, for fear of selecting a plan that's bad for the
	 * materialization case.
	 */
	if (slink->subLinkType == EXISTS_SUBLINK)
		tuple_fraction = 1.0;	/* just like a LIMIT 1 */
	else if (slink->subLinkType == ALL_SUBLINK ||
			 slink->subLinkType == ANY_SUBLINK)
		tuple_fraction = 0.5;	/* 50% */
	else
		tuple_fraction = 0.0;	/* default behavior */

	/*
	 * Generate the plan for the subquery.
	 */
	plan = subquery_planner(root->glob, subquery,
							root->query_level + 1,
							tuple_fraction,
							&subroot);

	/*
	 * Initialize the SubPlan node.  Note plan_id isn't set yet.
	 */
	splan = makeNode(SubPlan);
	splan->subLinkType = slink->subLinkType;
	splan->testexpr = NULL;
	splan->paramIds = NIL;
	splan->firstColType = get_first_col_type(plan);
	splan->useHashTable = false;
	/* At top level of a qual, can treat UNKNOWN the same as FALSE */
	splan->unknownEqFalse = isTopQual;
	splan->setParam = NIL;
	splan->parParam = NIL;
	splan->args = NIL;

	/*
	 * Make parParam list of params that current query level will pass to this
	 * child plan.
	 */
	tmpset = bms_copy(plan->extParam);
	while ((paramid = bms_first_member(tmpset)) >= 0)
	{
		PlannerParamItem *pitem = list_nth(root->glob->paramlist, paramid);

		if (pitem->abslevel == root->query_level)
			splan->parParam = lappend_int(splan->parParam, paramid);
	}
	bms_free(tmpset);

	/*
	 * Un-correlated or undirect correlated plans of EXISTS, EXPR, ARRAY, or
	 * ROWCOMPARE types can be used as initPlans.  For EXISTS, EXPR, or ARRAY,
	 * we just produce a Param referring to the result of evaluating the
	 * initPlan.  For ROWCOMPARE, we must modify the testexpr tree to contain
	 * PARAM_EXEC Params instead of the PARAM_SUBLINK Params emitted by the
	 * parser.
	 */
	if (splan->parParam == NIL && slink->subLinkType == EXISTS_SUBLINK)
	{
		Param	   *prm;

		prm = generate_new_param(root, BOOLOID, -1);
		splan->setParam = list_make1_int(prm->paramid);
		isInitPlan = true;
		result = (Node *) prm;
	}
	else if (splan->parParam == NIL && slink->subLinkType == EXPR_SUBLINK)
	{
		TargetEntry *te = linitial(plan->targetlist);
		Param	   *prm;

		Assert(!te->resjunk);
		prm = generate_new_param(root,
								 exprType((Node *) te->expr),
								 exprTypmod((Node *) te->expr));
		splan->setParam = list_make1_int(prm->paramid);
		isInitPlan = true;
		result = (Node *) prm;
	}
	else if (splan->parParam == NIL && slink->subLinkType == ARRAY_SUBLINK)
	{
		TargetEntry *te = linitial(plan->targetlist);
		Oid			arraytype;
		Param	   *prm;

		Assert(!te->resjunk);
		arraytype = get_array_type(exprType((Node *) te->expr));
		if (!OidIsValid(arraytype))
			elog(ERROR, "could not find array type for datatype %s",
				 format_type_be(exprType((Node *) te->expr)));
		prm = generate_new_param(root,
								 arraytype,
								 exprTypmod((Node *) te->expr));
		splan->setParam = list_make1_int(prm->paramid);
		isInitPlan = true;
		result = (Node *) prm;
	}
	else if (splan->parParam == NIL && slink->subLinkType == ROWCOMPARE_SUBLINK)
	{
		/* Adjust the Params */
		result = convert_testexpr(root,
								  testexpr,
								  0,
								  &splan->paramIds);
		splan->setParam = list_copy(splan->paramIds);
		isInitPlan = true;

		/*
		 * The executable expression is returned to become part of the outer
		 * plan's expression tree; it is not kept in the initplan node.
		 */
	}
	else
	{
		List	   *args;
		ListCell   *l;

		/* Adjust the Params */
		splan->testexpr = convert_testexpr(root,
										   testexpr,
										   0,
										   &splan->paramIds);

		/*
		 * We can't convert subplans of ALL_SUBLINK or ANY_SUBLINK types to
		 * initPlans, even when they are uncorrelated or undirect correlated,
		 * because we need to scan the output of the subplan for each outer
		 * tuple.  But if it's an IN (= ANY) test, we might be able to use a
		 * hashtable to avoid comparing all the tuples.
		 */
		if (subplan_is_hashable(slink, splan, plan))
			splan->useHashTable = true;

		/*
		 * Otherwise, we have the option to tack a MATERIAL node onto the top
		 * of the subplan, to reduce the cost of reading it repeatedly.  This
		 * is pointless for a direct-correlated subplan, since we'd have to
		 * recompute its results each time anyway.	For uncorrelated/undirect
		 * correlated subplans, we add MATERIAL unless the subplan's top plan
		 * node would materialize its output anyway.
		 */
		else if (splan->parParam == NIL)
		{
			bool		use_material;

			switch (nodeTag(plan))
			{
				case T_Material:
				case T_FunctionScan:
				case T_Sort:
					use_material = false;
					break;
				default:
					use_material = true;
					break;
			}
			if (use_material)
				plan = materialize_finished_plan(plan);
		}

		/*
		 * Make splan->args from parParam.
		 */
		args = NIL;
		foreach(l, splan->parParam)
		{
			PlannerParamItem *pitem = list_nth(root->glob->paramlist,
											   lfirst_int(l));

			/*
			 * The Var or Aggref has already been adjusted to have the correct
			 * varlevelsup or agglevelsup.	We probably don't even need to
			 * copy it again, but be safe.
			 */
			args = lappend(args, copyObject(pitem->item));
		}
		splan->args = args;

		result = (Node *) splan;
		isInitPlan = false;
	}

	/*
	 * Add the subplan and its rtable to the global lists.
	 */
	root->glob->subplans = lappend(root->glob->subplans,
								   plan);
	root->glob->subrtables = lappend(root->glob->subrtables,
									 subroot->parse->rtable);
	splan->plan_id = list_length(root->glob->subplans);

	if (isInitPlan)
		root->init_plans = lappend(root->init_plans, splan);

	/*
	 * A parameterless subplan (not initplan) should be prepared to handle
	 * REWIND efficiently.	If it has direct parameters then there's no point
	 * since it'll be reset on each scan anyway; and if it's an initplan then
	 * there's no point since it won't get re-run without parameter changes
	 * anyway.	The input of a hashed subplan doesn't need REWIND either.
	 */
	if (splan->parParam == NIL && !isInitPlan && !splan->useHashTable)
		root->glob->rewindPlanIDs = bms_add_member(root->glob->rewindPlanIDs,
												   splan->plan_id);

	return result;
}

/*
 * convert_testexpr: convert the testexpr given by the parser into
 * actually executable form.  This entails replacing PARAM_SUBLINK Params
 * with Params or Vars representing the results of the sub-select:
 *
 * If rtindex is 0, we build Params to represent the sub-select outputs.
 * The paramids of the Params created are returned in the *righthandIds list.
 *
 * If rtindex is not 0, we build Vars using that rtindex as varno.	Copies
 * of the Var nodes are returned in *righthandIds (this is a bit of a type
 * cheat, but we can get away with it).
 *
 * The given testexpr has already been recursively processed by
 * process_sublinks_mutator.  Hence it can no longer contain any
 * PARAM_SUBLINK Params for lower SubLink nodes; we can safely assume that
 * any we find are for our own level of SubLink.
 */
static Node *
convert_testexpr(PlannerInfo *root,
				 Node *testexpr,
				 int rtindex,
				 List **righthandIds)
{
	Node	   *result;
	convert_testexpr_context context;

	context.root = root;
	context.rtindex = rtindex;
	context.righthandIds = NIL;
	result = convert_testexpr_mutator(testexpr, &context);
	*righthandIds = context.righthandIds;
	return result;
}

static Node *
convert_testexpr_mutator(Node *node,
						 convert_testexpr_context *context)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, Param))
	{
		Param	   *param = (Param *) node;

		if (param->paramkind == PARAM_SUBLINK)
		{
			/*
			 * We expect to encounter the Params in column-number sequence. We
			 * could handle non-sequential order if necessary, but for now
			 * there's no need.  (This is also a useful cross-check that we
			 * aren't finding any unexpected Params.)
			 */
			if (param->paramid != list_length(context->righthandIds) + 1)
				elog(ERROR, "unexpected PARAM_SUBLINK ID: %d", param->paramid);

			if (context->rtindex)
			{
				/* Make the Var node representing the subplan's result */
				Var		   *newvar;

				newvar = makeVar(context->rtindex,
								 param->paramid,
								 param->paramtype,
								 param->paramtypmod,
								 0);

				/*
				 * Copy it for caller.	NB: we need a copy to avoid having
				 * doubly-linked substructure in the modified parse tree.
				 */
				context->righthandIds = lappend(context->righthandIds,
												copyObject(newvar));
				return (Node *) newvar;
			}
			else
			{
				/* Make the Param node representing the subplan's result */
				Param	   *newparam;

				newparam = generate_new_param(context->root,
											  param->paramtype,
											  param->paramtypmod);
				/* Record its ID */
				context->righthandIds = lappend_int(context->righthandIds,
													newparam->paramid);
				return (Node *) newparam;
			}
		}
	}
	return expression_tree_mutator(node,
								   convert_testexpr_mutator,
								   (void *) context);
}

/*
 * subplan_is_hashable: decide whether we can implement a subplan by hashing
 *
 * Caution: the SubPlan node is not completely filled in yet.  We can rely
 * on its plan and parParam fields, however.
 */
static bool
subplan_is_hashable(SubLink *slink, SubPlan *node, Plan *plan)
{
	double		subquery_size;
	ListCell   *l;

	/*
	 * The sublink type must be "= ANY" --- that is, an IN operator.  We
	 * expect that the test expression will be either a single OpExpr, or an
	 * AND-clause containing OpExprs.  (If it's anything else then the parser
	 * must have determined that the operators have non-equality-like
	 * semantics.  In the OpExpr case we can't be sure what the operator's
	 * semantics are like, but the test below for hashability will reject
	 * anything that's not equality.)
	 */
	if (slink->subLinkType != ANY_SUBLINK)
		return false;
	if (slink->testexpr == NULL ||
		(!IsA(slink->testexpr, OpExpr) &&
		 !and_clause(slink->testexpr)))
		return false;

	/*
	 * The subplan must not have any direct correlation vars --- else we'd
	 * have to recompute its output each time, so that the hashtable wouldn't
	 * gain anything.
	 */
	if (node->parParam != NIL)
		return false;

	/*
	 * The estimated size of the subquery result must fit in work_mem. (Note:
	 * we use sizeof(HeapTupleHeaderData) here even though the tuples will
	 * actually be stored as MinimalTuples; this provides some fudge factor
	 * for hashtable overhead.)
	 */
	subquery_size = plan->plan_rows *
		(MAXALIGN(plan->plan_width) + MAXALIGN(sizeof(HeapTupleHeaderData)));
	if (subquery_size > work_mem * 1024L)
		return false;

	/*
	 * The combining operators must be hashable and strict. The need for
	 * hashability is obvious, since we want to use hashing. Without
	 * strictness, behavior in the presence of nulls is too unpredictable.	We
	 * actually must assume even more than plain strictness: they can't yield
	 * NULL for non-null inputs, either (see nodeSubplan.c).  However, hash
	 * indexes and hash joins assume that too.
	 */
	if (IsA(slink->testexpr, OpExpr))
	{
		if (!hash_ok_operator((OpExpr *) slink->testexpr))
			return false;
	}
	else
	{
		foreach(l, ((BoolExpr *) slink->testexpr)->args)
		{
			Node	   *andarg = (Node *) lfirst(l);

			if (!IsA(andarg, OpExpr))
				return false;	/* probably can't happen */
			if (!hash_ok_operator((OpExpr *) andarg))
				return false;
		}
	}

	return true;
}

static bool
hash_ok_operator(OpExpr *expr)
{
	Oid			opid = expr->opno;
	HeapTuple	tup;
	Form_pg_operator optup;

	tup = SearchSysCache(OPEROID,
						 ObjectIdGetDatum(opid),
						 0, 0, 0);
	if (!HeapTupleIsValid(tup))
		elog(ERROR, "cache lookup failed for operator %u", opid);
	optup = (Form_pg_operator) GETSTRUCT(tup);
	if (!optup->oprcanhash || !func_strict(optup->oprcode))
	{
		ReleaseSysCache(tup);
		return false;
	}
	ReleaseSysCache(tup);
	return true;
}

/*
 * convert_IN_to_join: can we convert an IN SubLink to join style?
 *
 * The caller has found a SubLink at the top level of WHERE, but has not
 * checked the properties of the SubLink at all.  Decide whether it is
 * appropriate to process this SubLink in join style.  If not, return NULL.
 * If so, build the qual clause(s) to replace the SubLink, and return them.
 *
 * Side effects of a successful conversion include adding the SubLink's
 * subselect to the query's rangetable and adding an InClauseInfo node to
 * its in_info_list.
 */
Node *
convert_IN_to_join(PlannerInfo *root, SubLink *sublink)
{
	Query	   *parse = root->parse;
	Query	   *subselect = (Query *) sublink->subselect;
	List	   *in_operators;
	Relids		left_varnos;
	int			rtindex;
	RangeTblEntry *rte;
	RangeTblRef *rtr;
	InClauseInfo *ininfo;
	Node	   *result;

	/*
	 * The sublink type must be "= ANY" --- that is, an IN operator.  We
	 * expect that the test expression will be either a single OpExpr, or an
	 * AND-clause containing OpExprs.  (If it's anything else then the parser
	 * must have determined that the operators have non-equality-like
	 * semantics.  In the OpExpr case we can't be sure what the operator's
	 * semantics are like, and must check for ourselves.)
	 */
	if (sublink->subLinkType != ANY_SUBLINK)
		return NULL;
	if (sublink->testexpr && IsA(sublink->testexpr, OpExpr))
	{
		Oid			opno = ((OpExpr *) sublink->testexpr)->opno;
		List	   *opfamilies;
		List	   *opstrats;

		get_op_btree_interpretation(opno, &opfamilies, &opstrats);
		if (!list_member_int(opstrats, ROWCOMPARE_EQ))
			return NULL;
		in_operators = list_make1_oid(opno);
	}
	else if (and_clause(sublink->testexpr))
	{
		ListCell   *lc;

		/* OK, but we need to extract the per-column operator OIDs */
		in_operators = NIL;
		foreach(lc, ((BoolExpr *) sublink->testexpr)->args)
		{
			OpExpr	   *op = (OpExpr *) lfirst(lc);

			if (!IsA(op, OpExpr))		/* probably shouldn't happen */
				return NULL;
			in_operators = lappend_oid(in_operators, op->opno);
		}
	}
	else
		return NULL;

	/*
	 * The sub-select must not refer to any Vars of the parent query. (Vars of
	 * higher levels should be okay, though.)
	 */
	if (contain_vars_of_level((Node *) subselect, 1))
		return NULL;

	/*
	 * The left-hand expressions must contain some Vars of the current query,
	 * else it's not gonna be a join.
	 */
	left_varnos = pull_varnos(sublink->testexpr);
	if (bms_is_empty(left_varnos))
		return NULL;

	/*
	 * The combining operators and left-hand expressions mustn't be volatile.
	 */
	if (contain_volatile_functions(sublink->testexpr))
		return NULL;

	/*
	 * Okay, pull up the sub-select into top range table and jointree.
	 *
	 * We rely here on the assumption that the outer query has no references
	 * to the inner (necessarily true, other than the Vars that we build
	 * below). Therefore this is a lot easier than what pull_up_subqueries has
	 * to go through.
	 */
	rte = addRangeTableEntryForSubquery(NULL,
										subselect,
										makeAlias("IN_subquery", NIL),
										false);
	parse->rtable = lappend(parse->rtable, rte);
	rtindex = list_length(parse->rtable);
	rtr = makeNode(RangeTblRef);
	rtr->rtindex = rtindex;
	parse->jointree->fromlist = lappend(parse->jointree->fromlist, rtr);

	/*
	 * Now build the InClauseInfo node.
	 */
	ininfo = makeNode(InClauseInfo);
	ininfo->lefthand = left_varnos;
	ininfo->righthand = bms_make_singleton(rtindex);
	ininfo->in_operators = in_operators;

	/*
	 * Build the result qual expression.  As a side effect,
	 * ininfo->sub_targetlist is filled with a list of Vars representing the
	 * subselect outputs.
	 */
	result = convert_testexpr(root,
							  sublink->testexpr,
							  rtindex,
							  &ininfo->sub_targetlist);

	Assert(list_length(in_operators) == list_length(ininfo->sub_targetlist));

	/* Add the completed node to the query's list */
	root->in_info_list = lappend(root->in_info_list, ininfo);

	return result;
}

/*
 * Replace correlation vars (uplevel vars) with Params.
 *
 * Uplevel aggregates are replaced, too.
 *
 * Note: it is critical that this runs immediately after SS_process_sublinks.
 * Since we do not recurse into the arguments of uplevel aggregates, they will
 * get copied to the appropriate subplan args list in the parent query with
 * uplevel vars not replaced by Params, but only adjusted in level (see
 * replace_outer_agg).	That's exactly what we want for the vars of the parent
 * level --- but if an aggregate's argument contains any further-up variables,
 * they have to be replaced with Params in their turn.	That will happen when
 * the parent level runs SS_replace_correlation_vars.  Therefore it must do
 * so after expanding its sublinks to subplans.  And we don't want any steps
 * in between, else those steps would never get applied to the aggregate
 * argument expressions, either in the parent or the child level.
 */
Node *
SS_replace_correlation_vars(PlannerInfo *root, Node *expr)
{
	/* No setup needed for tree walk, so away we go */
	return replace_correlation_vars_mutator(expr, root);
}

static Node *
replace_correlation_vars_mutator(Node *node, PlannerInfo *root)
{
	if (node == NULL)
		return NULL;
	if (IsA(node, Var))
	{
		if (((Var *) node)->varlevelsup > 0)
			return (Node *) replace_outer_var(root, (Var *) node);
	}
	if (IsA(node, Aggref))
	{
		if (((Aggref *) node)->agglevelsup > 0)
			return (Node *) replace_outer_agg(root, (Aggref *) node);
	}
	return expression_tree_mutator(node,
								   replace_correlation_vars_mutator,
								   (void *) root);
}

/*
 * Expand SubLinks to SubPlans in the given expression.
 *
 * The isQual argument tells whether or not this expression is a WHERE/HAVING
 * qualifier expression.  If it is, any sublinks appearing at top level need
 * not distinguish FALSE from UNKNOWN return values.
 */
Node *
SS_process_sublinks(PlannerInfo *root, Node *expr, bool isQual)
{
	process_sublinks_context context;

	context.root = root;
	context.isTopQual = isQual;
	return process_sublinks_mutator(expr, &context);
}

static Node *
process_sublinks_mutator(Node *node, process_sublinks_context * context)
{
	process_sublinks_context locContext;

	locContext.root = context->root;

	if (node == NULL)
		return NULL;
	if (IsA(node, SubLink))
	{
		SubLink    *sublink = (SubLink *) node;
		Node	   *testexpr;

		/*
		 * First, recursively process the lefthand-side expressions, if any.
		 * They're not top-level anymore.
		 */
		locContext.isTopQual = false;
		testexpr = process_sublinks_mutator(sublink->testexpr, &locContext);

		/*
		 * Now build the SubPlan node and make the expr to return.
		 */
		return make_subplan(context->root,
							sublink,
							testexpr,
							context->isTopQual);
	}

	/*
	 * We should never see a SubPlan expression in the input (since this is
	 * the very routine that creates 'em to begin with).  We shouldn't find
	 * ourselves invoked directly on a Query, either.
	 */
	Assert(!is_subplan(node));
	Assert(!IsA(node, Query));

	/*
	 * Because make_subplan() could return an AND or OR clause, we have to
	 * take steps to preserve AND/OR flatness of a qual.  We assume the input
	 * has been AND/OR flattened and so we need no recursion here.
	 *
	 * If we recurse down through anything other than an AND node, we are
	 * definitely not at top qual level anymore.  (Due to the coding here, we
	 * will not get called on the List subnodes of an AND, so no check is
	 * needed for List.)
	 */
	if (and_clause(node))
	{
		List	   *newargs = NIL;
		ListCell   *l;

		/* Still at qual top-level */
		locContext.isTopQual = context->isTopQual;

		foreach(l, ((BoolExpr *) node)->args)
		{
			Node	   *newarg;

			newarg = process_sublinks_mutator(lfirst(l), &locContext);
			if (and_clause(newarg))
				newargs = list_concat(newargs, ((BoolExpr *) newarg)->args);
			else
				newargs = lappend(newargs, newarg);
		}
		return (Node *) make_andclause(newargs);
	}

	/* otherwise not at qual top-level */
	locContext.isTopQual = false;

	if (or_clause(node))
	{
		List	   *newargs = NIL;
		ListCell   *l;

		foreach(l, ((BoolExpr *) node)->args)
		{
			Node	   *newarg;

			newarg = process_sublinks_mutator(lfirst(l), &locContext);
			if (or_clause(newarg))
				newargs = list_concat(newargs, ((BoolExpr *) newarg)->args);
			else
				newargs = lappend(newargs, newarg);
		}
		return (Node *) make_orclause(newargs);
	}

	return expression_tree_mutator(node,
								   process_sublinks_mutator,
								   (void *) &locContext);
}

/*
 * SS_finalize_plan - do final sublink processing for a completed Plan.
 *
 * This recursively computes the extParam and allParam sets for every Plan
 * node in the given plan tree.  It also attaches any generated InitPlans
 * to the top plan node.
 */
void
SS_finalize_plan(PlannerInfo *root, Plan *plan)
{
	Bitmapset  *outer_params,
			   *valid_params,
			   *initExtParam,
			   *initSetParam;
	Cost		initplan_cost;
	int			paramid;
	ListCell   *l;

	/*
	 * First, scan the param list to discover the sets of params that are
	 * available from outer query levels and my own query level. We do this
	 * once to save time in the per-plan recursion steps.
	 */
	outer_params = valid_params = NULL;
	paramid = 0;
	foreach(l, root->glob->paramlist)
	{
		PlannerParamItem *pitem = (PlannerParamItem *) lfirst(l);

		if (pitem->abslevel < root->query_level)
		{
			/* valid outer-level parameter */
			outer_params = bms_add_member(outer_params, paramid);
			valid_params = bms_add_member(valid_params, paramid);
		}
		else if (pitem->abslevel == root->query_level &&
				 IsA(pitem->item, Param))
		{
			/* valid local parameter (i.e., a setParam of my child) */
			valid_params = bms_add_member(valid_params, paramid);
		}

		paramid++;
	}

	/*
	 * Now recurse through plan tree.
	 */
	(void) finalize_plan(root, plan, outer_params, valid_params);

	bms_free(outer_params);
	bms_free(valid_params);

	/*
	 * Finally, attach any initPlans to the topmost plan node, and add their
	 * extParams to the topmost node's, too.  However, any setParams of the
	 * initPlans should not be present in the topmost node's extParams, only
	 * in its allParams.  (As of PG 8.1, it's possible that some initPlans
	 * have extParams that are setParams of other initPlans, so we have to
	 * take care of this situation explicitly.)
	 *
	 * We also add the eval cost of each initPlan to the startup cost of the
	 * top node.  This is a conservative overestimate, since in fact each
	 * initPlan might be executed later than plan startup, or even not at all.
	 */
	plan->initPlan = root->init_plans;
	root->init_plans = NIL;		/* make sure they're not attached twice */

	initExtParam = initSetParam = NULL;
	initplan_cost = 0;
	foreach(l, plan->initPlan)
	{
		SubPlan    *initsubplan = (SubPlan *) lfirst(l);
		Plan	   *initplan = planner_subplan_get_plan(root, initsubplan);
		ListCell   *l2;

		initExtParam = bms_add_members(initExtParam, initplan->extParam);
		foreach(l2, initsubplan->setParam)
		{
			initSetParam = bms_add_member(initSetParam, lfirst_int(l2));
		}
		initplan_cost += get_initplan_cost(root, initsubplan);
	}
	/* allParam must include all these params */
	plan->allParam = bms_add_members(plan->allParam, initExtParam);
	plan->allParam = bms_add_members(plan->allParam, initSetParam);
	/* but extParam shouldn't include any setParams */
	initExtParam = bms_del_members(initExtParam, initSetParam);
	/* empty test ensures extParam is exactly NULL if it's empty */
	if (!bms_is_empty(initExtParam))
		plan->extParam = bms_join(plan->extParam, initExtParam);

	plan->startup_cost += initplan_cost;
	plan->total_cost += initplan_cost;
}

/*
 * Recursive processing of all nodes in the plan tree
 *
 * The return value is the computed allParam set for the given Plan node.
 * This is just an internal notational convenience.
 */
static Bitmapset *
finalize_plan(PlannerInfo *root, Plan *plan,
			  Bitmapset *outer_params, Bitmapset *valid_params)
{
	finalize_primnode_context context;

	if (plan == NULL)
		return NULL;

	context.root = root;
	context.paramids = NULL;	/* initialize set to empty */
	context.outer_params = outer_params;

	/*
	 * When we call finalize_primnode, context.paramids sets are automatically
	 * merged together.  But when recursing to self, we have to do it the hard
	 * way.  We want the paramids set to include params in subplans as well as
	 * at this level.
	 */

	/* Find params in targetlist and qual */
	finalize_primnode((Node *) plan->targetlist, &context);
	finalize_primnode((Node *) plan->qual, &context);

	/* Check additional node-type-specific fields */
	switch (nodeTag(plan))
	{
		case T_Result:
			finalize_primnode(((Result *) plan)->resconstantqual,
							  &context);
			break;

		case T_IndexScan:
			finalize_primnode((Node *) ((IndexScan *) plan)->indexqual,
							  &context);

			/*
			 * we need not look at indexqualorig, since it will have the same
			 * param references as indexqual.
			 */
			break;

		case T_BitmapIndexScan:
			finalize_primnode((Node *) ((BitmapIndexScan *) plan)->indexqual,
							  &context);

			/*
			 * we need not look at indexqualorig, since it will have the same
			 * param references as indexqual.
			 */
			break;

		case T_BitmapHeapScan:
			finalize_primnode((Node *) ((BitmapHeapScan *) plan)->bitmapqualorig,
							  &context);
			break;

		case T_TidScan:
			finalize_primnode((Node *) ((TidScan *) plan)->tidquals,
							  &context);
			break;

		case T_SubqueryScan:

			/*
			 * In a SubqueryScan, SS_finalize_plan has already been run on the
			 * subplan by the inner invocation of subquery_planner, so there's
			 * no need to do it again.	Instead, just pull out the subplan's
			 * extParams list, which represents the params it needs from my
			 * level and higher levels.
			 */
			context.paramids = bms_add_members(context.paramids,
								 ((SubqueryScan *) plan)->subplan->extParam);
			break;

		case T_FunctionScan:
			finalize_primnode(((FunctionScan *) plan)->funcexpr,
							  &context);
			break;

		case T_ValuesScan:
			finalize_primnode((Node *) ((ValuesScan *) plan)->values_lists,
							  &context);
			break;

		case T_Append:
			{
				ListCell   *l;

				foreach(l, ((Append *) plan)->appendplans)
				{
					context.paramids =
						bms_add_members(context.paramids,
										finalize_plan(root,
													  (Plan *) lfirst(l),
													  outer_params,
													  valid_params));
				}
			}
			break;

		case T_BitmapAnd:
			{
				ListCell   *l;

				foreach(l, ((BitmapAnd *) plan)->bitmapplans)
				{
					context.paramids =
						bms_add_members(context.paramids,
										finalize_plan(root,
													  (Plan *) lfirst(l),
													  outer_params,
													  valid_params));
				}
			}
			break;

		case T_BitmapOr:
			{
				ListCell   *l;

				foreach(l, ((BitmapOr *) plan)->bitmapplans)
				{
					context.paramids =
						bms_add_members(context.paramids,
										finalize_plan(root,
													  (Plan *) lfirst(l),
													  outer_params,
													  valid_params));
				}
			}
			break;

		case T_NestLoop:
			finalize_primnode((Node *) ((Join *) plan)->joinqual,
							  &context);
			break;

		case T_MergeJoin:
			finalize_primnode((Node *) ((Join *) plan)->joinqual,
							  &context);
			finalize_primnode((Node *) ((MergeJoin *) plan)->mergeclauses,
							  &context);
			break;

		case T_HashJoin:
			finalize_primnode((Node *) ((Join *) plan)->joinqual,
							  &context);
			finalize_primnode((Node *) ((HashJoin *) plan)->hashclauses,
							  &context);
			break;

		case T_Limit:
			finalize_primnode(((Limit *) plan)->limitOffset,
							  &context);
			finalize_primnode(((Limit *) plan)->limitCount,
							  &context);
			break;

		case T_Hash:
		case T_Agg:
		case T_SeqScan:
		case T_Material:
		case T_Sort:
		case T_Unique:
		case T_SetOp:
		case T_Group:
			break;

		default:
			elog(ERROR, "unrecognized node type: %d",
				 (int) nodeTag(plan));
	}

	/* Process left and right child plans, if any */
	context.paramids = bms_add_members(context.paramids,
									   finalize_plan(root,
													 plan->lefttree,
													 outer_params,
													 valid_params));

	context.paramids = bms_add_members(context.paramids,
									   finalize_plan(root,
													 plan->righttree,
													 outer_params,
													 valid_params));

	/* Now we have all the paramids */

	if (!bms_is_subset(context.paramids, valid_params))
		elog(ERROR, "plan should not reference subplan's variable");

	plan->extParam = bms_intersect(context.paramids, outer_params);
	plan->allParam = context.paramids;

	/*
	 * For speed at execution time, make sure extParam/allParam are actually
	 * NULL if they are empty sets.
	 */
	if (bms_is_empty(plan->extParam))
	{
		bms_free(plan->extParam);
		plan->extParam = NULL;
	}
	if (bms_is_empty(plan->allParam))
	{
		bms_free(plan->allParam);
		plan->allParam = NULL;
	}

	return plan->allParam;
}

/*
 * finalize_primnode: add IDs of all PARAM_EXEC params appearing in the given
 * expression tree to the result set.
 */
static bool
finalize_primnode(Node *node, finalize_primnode_context *context)
{
	if (node == NULL)
		return false;
	if (IsA(node, Param))
	{
		if (((Param *) node)->paramkind == PARAM_EXEC)
		{
			int			paramid = ((Param *) node)->paramid;

			context->paramids = bms_add_member(context->paramids, paramid);
		}
		return false;			/* no more to do here */
	}
	if (is_subplan(node))
	{
		SubPlan    *subplan = (SubPlan *) node;
		Plan	   *plan = planner_subplan_get_plan(context->root, subplan);

		/* Add outer-level params needed by the subplan to paramids */
		context->paramids = bms_join(context->paramids,
									 bms_intersect(plan->extParam,
												   context->outer_params));
		/* fall through to recurse into subplan args */
	}
	return expression_tree_walker(node, finalize_primnode,
								  (void *) context);
}

/*
 * SS_make_initplan_from_plan - given a plan tree, make it an InitPlan
 *
 * The plan is expected to return a scalar value of the indicated type.
 * We build an EXPR_SUBLINK SubPlan node and put it into the initplan
 * list for the current query level.  A Param that represents the initplan's
 * output is returned.
 *
 * We assume the plan hasn't been put through SS_finalize_plan.
 */
Param *
SS_make_initplan_from_plan(PlannerInfo *root, Plan *plan,
						   Oid resulttype, int32 resulttypmod)
{
	List	   *saved_init_plans;
	SubPlan    *node;
	Param	   *prm;

	/*
	 * We must run SS_finalize_plan(), since that's normally done before a
	 * subplan gets put into the initplan list.  However it will try to attach
	 * any pre-existing initplans to this one, which we don't want (they are
	 * siblings not children of this initplan).  So, a quick kluge to hide
	 * them.  (This is something else that could perhaps be cleaner if we did
	 * extParam/allParam processing in setrefs.c instead of here?  See notes
	 * for materialize_finished_plan.)
	 */
	saved_init_plans = root->init_plans;
	root->init_plans = NIL;

	/*
	 * Build extParam/allParam sets for plan nodes.
	 */
	SS_finalize_plan(root, plan);

	/* Restore outer initplan list */
	root->init_plans = saved_init_plans;

	/*
	 * Add the subplan and its rtable to the global lists.
	 */
	root->glob->subplans = lappend(root->glob->subplans,
								   plan);
	root->glob->subrtables = lappend(root->glob->subrtables,
									 root->parse->rtable);

	/*
	 * Create a SubPlan node and add it to the outer list of InitPlans.
	 */
	node = makeNode(SubPlan);
	node->subLinkType = EXPR_SUBLINK;
	node->firstColType = get_first_col_type(plan);
	node->plan_id = list_length(root->glob->subplans);

	root->init_plans = lappend(root->init_plans, node);

	/*
	 * The node can't have any inputs (since it's an initplan), so the
	 * parParam and args lists remain empty.
	 */

	/*
	 * Make a Param that will be the subplan's output.
	 */
	prm = generate_new_param(root, resulttype, resulttypmod);
	node->setParam = list_make1_int(prm->paramid);

	return prm;
}