[postgresql] / 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 1.116 2007/01/05 22:19:32 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/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"


Index           PlannerQueryLevel;      /* level of current query */
List       *PlannerInitPlan;    /* init subplans for current query */
List       *PlannerParamList;   /* to keep track of cross-level Params */

int                     PlannerPlanId = 0;      /* to assign unique ID to subquery plans */

/*
 * PlannerParamList keeps track of the PARAM_EXEC slots that we have decided
 * we need for the query.  At runtime these slots are used to pass values
 * either down into subqueries (for outer references in subqueries) or up out
 * of subqueries (for the results of a subplan).  The n'th entry in the list
 * (n counts from 0) corresponds to Param->paramid = n.
 *
 * Each ParamList item shows the absolute query level it is associated with,
 * where the outermost query is level 1 and nested subqueries have higher
 * numbers.  The item the parameter slot represents can be one of three kinds:
 *
 * A Var: the slot represents a variable of that level that must be passed
 * down because subqueries have outer references to it.  The varlevelsup
 * value in the Var will always be zero.
 *
 * An Aggref (with an expression tree representing its argument): the slot
 * represents an aggregate expression that is an outer reference for some
 * subquery.  The Aggref itself has agglevelsup = 0, and its argument tree
 * is adjusted to match in level.
 *
 * A Param: the slot holds the result of a subplan (it is a setParam item
 * for that subplan).  The absolute level shown for such items corresponds
 * to the parent query of the subplan.
 *
 * Note: we detect duplicate Var parameters and coalesce them into one slot,
 * but we do not do this for Aggref or Param slots.
 */
typedef struct PlannerParamItem
{
        Node       *item;                       /* the Var, Aggref, or Param */
        Index           abslevel;               /* its absolute query level */
} PlannerParamItem;


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

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


static Node *convert_testexpr(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);
static bool hash_ok_operator(OpExpr *expr);
static Node *replace_correlation_vars_mutator(Node *node, void *context);
static Node *process_sublinks_mutator(Node *node, bool *isTopQual);
static Bitmapset *finalize_plan(Plan *plan, List *rtable,
                          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(Var *var)
{
        Param      *retval;
        ListCell   *ppl;
        PlannerParamItem *pitem;
        Index           abslevel;
        int                     i;

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

        /*
         * If there's already a PlannerParamList 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, PlannerParamList)
        {
                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 = (PlannerParamItem *) palloc(sizeof(PlannerParamItem));
                pitem->item = (Node *) var;
                pitem->abslevel = abslevel;

                PlannerParamList = lappend(PlannerParamList, 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(Aggref *agg)
{
        Param      *retval;
        PlannerParamItem *pitem;
        Index           abslevel;
        int                     i;

        Assert(agg->agglevelsup > 0 && agg->agglevelsup < PlannerQueryLevel);
        abslevel = PlannerQueryLevel - 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 = (PlannerParamItem *) palloc(sizeof(PlannerParamItem));
        pitem->item = (Node *) agg;
        pitem->abslevel = abslevel;

        PlannerParamList = lappend(PlannerParamList, pitem);
        i = list_length(PlannerParamList) - 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(Oid paramtype, int32 paramtypmod)
{
        Param      *retval;
        PlannerParamItem *pitem;

        retval = makeNode(Param);
        retval->paramkind = PARAM_EXEC;
        retval->paramid = list_length(PlannerParamList);
        retval->paramtype = paramtype;
        retval->paramtypmod = paramtypmod;

        pitem = (PlannerParamItem *) palloc(sizeof(PlannerParamItem));
        pitem->item = (Node *) retval;
        pitem->abslevel = PlannerQueryLevel;

        PlannerParamList = lappend(PlannerParamList, pitem);

        return retval;
}

/*
 * 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(SubLink *slink, Node *testexpr, bool isTopQual)
{
        SubPlan    *node = makeNode(SubPlan);
        Query      *subquery = (Query *) (slink->subselect);
        double          tuple_fraction;
        Plan       *plan;
        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()
         * 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.
         */
        node->plan = plan = subquery_planner(subquery, tuple_fraction, NULL);

        node->plan_id = PlannerPlanId++;        /* Assign unique ID to this SubPlan */

        node->rtable = subquery->rtable;

        /*
         * Initialize other fields of the SubPlan node.
         */
        node->subLinkType = slink->subLinkType;
        node->testexpr = NULL;
        node->paramIds = NIL;
        node->useHashTable = false;
        /* At top level of a qual, can treat UNKNOWN the same as FALSE */
        node->unknownEqFalse = isTopQual;
        node->setParam = NIL;
        node->parParam = NIL;
        node->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(PlannerParamList, paramid);

                if (pitem->abslevel == PlannerQueryLevel)
                        node->parParam = lappend_int(node->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 (node->parParam == NIL && slink->subLinkType == EXISTS_SUBLINK)
        {
                Param      *prm;

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

                Assert(!te->resjunk);
                prm = generate_new_param(exprType((Node *) te->expr),
                                                                 exprTypmod((Node *) te->expr));
                node->setParam = list_make1_int(prm->paramid);
                PlannerInitPlan = lappend(PlannerInitPlan, node);
                result = (Node *) prm;
        }
        else if (node->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(arraytype, exprTypmod((Node *) te->expr));
                node->setParam = list_make1_int(prm->paramid);
                PlannerInitPlan = lappend(PlannerInitPlan, node);
                result = (Node *) prm;
        }
        else if (node->parParam == NIL && slink->subLinkType == ROWCOMPARE_SUBLINK)
        {
                /* Adjust the Params */
                result = convert_testexpr(testexpr,
                                                                  0,
                                                                  &node->paramIds);
                node->setParam = list_copy(node->paramIds);
                PlannerInitPlan = lappend(PlannerInitPlan, node);

                /*
                 * 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 */
                node->testexpr = convert_testexpr(testexpr,
                                                                                  0,
                                                                                  &node->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, node))
                        node->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 (node->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)
                                node->plan = plan = materialize_finished_plan(plan);
                }

                /*
                 * Make node->args from parParam.
                 */
                args = NIL;
                foreach(l, node->parParam)
                {
                        PlannerParamItem *pitem = list_nth(PlannerParamList, 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));
                }
                node->args = args;

                result = (Node *) node;
        }

        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(Node *testexpr,
                                 int rtindex,
                                 List **righthandIds)
{
        Node       *result;
        convert_testexpr_context context;

        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(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)
{
        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 = node->plan->plan_rows *
                (MAXALIGN(node->plan->plan_width) + MAXALIGN(sizeof(HeapTupleHeaderData)));
        if (subquery_size > work_mem * 1024L)
                return false;

        /*
         * The combining operators must be hashable, strict, and self-commutative.
         * 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, see nodeSubplan.c for details.)  And commutativity ensures
         * that the left and right datatypes are the same; this allows us to
         * assume that the combining operators are equality for the righthand
         * datatype, so that they can be used to compare righthand tuples as well
         * as comparing lefthand to righthand tuples.  (This last restriction
         * could be relaxed by using two different sets of operators with the hash
         * table, but there is no obvious usefulness to that at present.)
         */
        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 || optup->oprcom != opid ||
                !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;
        Relids          left_varnos;
        int                     rtindex;
        RangeTblEntry *rte;
        RangeTblRef *rtr;
        InClauseInfo *ininfo;

        /*
         * 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))
        {
                List       *opfamilies;
                List       *opstrats;

                get_op_btree_interpretation(((OpExpr *) sublink->testexpr)->opno,
                                                                        &opfamilies, &opstrats);
                if (!list_member_int(opstrats, ROWCOMPARE_EQ))
                        return NULL;
        }
        else if (!and_clause(sublink->testexpr))
                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);
        root->in_info_list = lappend(root->in_info_list, ininfo);

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

/*
 * 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(Node *expr)
{
        /* No setup needed for tree walk, so away we go */
        return replace_correlation_vars_mutator(expr, NULL);
}

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

/*
 * 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(Node *expr, bool isQual)
{
        /* The only context needed is the initial are-we-in-a-qual flag */
        return process_sublinks_mutator(expr, &isQual);
}

static Node *
process_sublinks_mutator(Node *node, bool *isTopQual)
{
        bool            locTopQual;

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

                /*
                 * First, recursively process the lefthand-side expressions, if any.
                 */
                locTopQual = false;
                testexpr = process_sublinks_mutator(sublink->testexpr, &locTopQual);

                /*
                 * Now build the SubPlan node and make the expr to return.
                 */
                return make_subplan(sublink, testexpr, *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 */
                locTopQual = *isTopQual;

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

                        newarg = process_sublinks_mutator(lfirst(l),
                                                                                          (void *) &locTopQual);
                        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 */
        locTopQual = false;

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

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

                        newarg = process_sublinks_mutator(lfirst(l),
                                                                                          (void *) &locTopQual);
                        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 *) &locTopQual);
}

/*
 * 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(Plan *plan, List *rtable)
{
        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, PlannerParamList)
        {
                PlannerParamItem *pitem = (PlannerParamItem *) lfirst(l);

                if (pitem->abslevel < PlannerQueryLevel)
                {
                        /* valid outer-level parameter */
                        outer_params = bms_add_member(outer_params, paramid);
                        valid_params = bms_add_member(valid_params, paramid);
                }
                else if (pitem->abslevel == PlannerQueryLevel &&
                                 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(plan, rtable, 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 total_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 = PlannerInitPlan;
        PlannerInitPlan = NIL;          /* make sure they're not attached twice */

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

                initExtParam = bms_add_members(initExtParam,
                                                                           initplan->plan->extParam);
                foreach(l2, initplan->setParam)
                {
                        initSetParam = bms_add_member(initSetParam, lfirst_int(l2));
                }
                initplan_cost += initplan->plan->total_cost;
        }
        /* 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(Plan *plan, List *rtable,
                          Bitmapset *outer_params, Bitmapset *valid_params)
{
        finalize_primnode_context context;

        if (plan == NULL)
                return NULL;

        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:
                        {
                                RangeTblEntry *rte;

                                rte = rt_fetch(((FunctionScan *) plan)->scan.scanrelid,
                                                           rtable);
                                Assert(rte->rtekind == RTE_FUNCTION);
                                finalize_primnode(rte->funcexpr, &context);
                        }
                        break;

                case T_ValuesScan:
                        {
                                RangeTblEntry *rte;

                                rte = rt_fetch(((ValuesScan *) plan)->scan.scanrelid,
                                                           rtable);
                                Assert(rte->rtekind == RTE_VALUES);
                                finalize_primnode((Node *) rte->values_lists, &context);
                        }
                        break;

                case T_Append:
                        {
                                ListCell   *l;

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

                case T_BitmapAnd:
                        {
                                ListCell   *l;

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

                case T_BitmapOr:
                        {
                                ListCell   *l;

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

        context.paramids = bms_add_members(context.paramids,
                                                                           finalize_plan(plan->righttree,
                                                                                                         rtable,
                                                                                                         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;

                /* Add outer-level params needed by the subplan to paramids */
                context->paramids = bms_join(context->paramids,
                                                                         bms_intersect(subplan->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_initplan = PlannerInitPlan;
        SubPlan    *node;
        Param      *prm;

        /*
         * Set up for a new level of subquery.  This is just to keep
         * SS_finalize_plan from becoming confused.
         */
        PlannerQueryLevel++;
        PlannerInitPlan = NIL;

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

        /* Return to outer subquery context */
        PlannerQueryLevel--;
        PlannerInitPlan = saved_initplan;

        /*
         * Create a SubPlan node and add it to the outer list of InitPlans.
         */
        node = makeNode(SubPlan);
        node->subLinkType = EXPR_SUBLINK;
        node->plan = plan;
        node->plan_id = PlannerPlanId++;        /* Assign unique ID to this SubPlan */

        node->rtable = root->parse->rtable;

        PlannerInitPlan = lappend(PlannerInitPlan, 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(resulttype, resulttypmod);
        node->setParam = list_make1_int(prm->paramid);

        return prm;
}