nodeSubplan.c

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/*-------------------------------------------------------------------------
 *
 * nodeSubplan.c
 *    routines to support subselects
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeSubplan.c
 *
 *-------------------------------------------------------------------------
 */
/*
 *   INTERFACE ROUTINES
 *      ExecSubPlan  - process a subselect
 *      ExecInitSubPlan - initialize a subselect
 */
#include "postgres.h"

#include <limits.h>
#include <math.h>

#include "access/htup_details.h"
#include "executor/executor.h"
#include "executor/nodeSubplan.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "utils/array.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"


static Datum ExecSubPlan(SubPlanState *node,
            ExprContext *econtext,
            bool *isNull,
            ExprDoneCond *isDone);
static Datum ExecAlternativeSubPlan(AlternativeSubPlanState *node,
                       ExprContext *econtext,
                       bool *isNull,
                       ExprDoneCond *isDone);
static Datum ExecHashSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull);
static Datum ExecScanSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull);
static void buildSubPlanHash(SubPlanState *node, ExprContext *econtext);
static bool findPartialMatch(TupleHashTable hashtable, TupleTableSlot *slot,
                 FmgrInfo *eqfunctions);
static bool slotAllNulls(TupleTableSlot *slot);
static bool slotNoNulls(TupleTableSlot *slot);


/* ----------------------------------------------------------------
 *      ExecSubPlan
 * ----------------------------------------------------------------
 */
static Datum
ExecSubPlan(SubPlanState *node,
            ExprContext *econtext,
            bool *isNull,
            ExprDoneCond *isDone)
{
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;

    /* Set default values for result flags: non-null, not a set result */
    *isNull = false;
    if (isDone)
        *isDone = ExprSingleResult;

    /* Sanity checks */
    if (subplan->subLinkType == CTE_SUBLINK)
        elog(ERROR, "CTE subplans should not be executed via ExecSubPlan");
    if (subplan->setParam != NIL)
        elog(ERROR, "cannot set parent params from subquery");

    /* Select appropriate evaluation strategy */
    if (subplan->useHashTable)
        return ExecHashSubPlan(node, econtext, isNull);
    else
        return ExecScanSubPlan(node, econtext, isNull);
}

/*
 * ExecHashSubPlan: store subselect result in an in-memory hash table
 */
static Datum
ExecHashSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull)
{
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
    PlanState  *planstate = node->planstate;
    TupleTableSlot *slot;

    /* Shouldn't have any direct correlation Vars */
    if (subplan->parParam != NIL || node->args != NIL)
        elog(ERROR, "hashed subplan with direct correlation not supported");

    /*
     * If first time through or we need to rescan the subplan, build the hash
     * table.
     */
    if (node->hashtable == NULL || planstate->chgParam != NULL)
        buildSubPlanHash(node, econtext);

    /*
     * The result for an empty subplan is always FALSE; no need to evaluate
     * lefthand side.
     */
    *isNull = false;
    if (!node->havehashrows && !node->havenullrows)
        return BoolGetDatum(false);

    /*
     * Evaluate lefthand expressions and form a projection tuple. First we
     * have to set the econtext to use (hack alert!).
     */
    node->projLeft->pi_exprContext = econtext;
    slot = ExecProject(node->projLeft, NULL);

    /*
     * Note: because we are typically called in a per-tuple context, we have
     * to explicitly clear the projected tuple before returning. Otherwise,
     * we'll have a double-free situation: the per-tuple context will probably
     * be reset before we're called again, and then the tuple slot will think
     * it still needs to free the tuple.
     */

    /*
     * If the LHS is all non-null, probe for an exact match in the main hash
     * table.  If we find one, the result is TRUE. Otherwise, scan the
     * partly-null table to see if there are any rows that aren't provably
     * unequal to the LHS; if so, the result is UNKNOWN.  (We skip that part
     * if we don't care about UNKNOWN.) Otherwise, the result is FALSE.
     *
     * Note: the reason we can avoid a full scan of the main hash table is
     * that the combining operators are assumed never to yield NULL when both
     * inputs are non-null.  If they were to do so, we might need to produce
     * UNKNOWN instead of FALSE because of an UNKNOWN result in comparing the
     * LHS to some main-table entry --- which is a comparison we will not even
     * make, unless there's a chance match of hash keys.
     */
    if (slotNoNulls(slot))
    {
        if (node->havehashrows &&
            FindTupleHashEntry(node->hashtable,
                               slot,
                               node->cur_eq_funcs,
                               node->lhs_hash_funcs) != NULL)
        {
            ExecClearTuple(slot);
            return BoolGetDatum(true);
        }
        if (node->havenullrows &&
            findPartialMatch(node->hashnulls, slot, node->cur_eq_funcs))
        {
            ExecClearTuple(slot);
            *isNull = true;
            return BoolGetDatum(false);
        }
        ExecClearTuple(slot);
        return BoolGetDatum(false);
    }

    /*
     * When the LHS is partly or wholly NULL, we can never return TRUE. If we
     * don't care about UNKNOWN, just return FALSE.  Otherwise, if the LHS is
     * wholly NULL, immediately return UNKNOWN.  (Since the combining
     * operators are strict, the result could only be FALSE if the sub-select
     * were empty, but we already handled that case.) Otherwise, we must scan
     * both the main and partly-null tables to see if there are any rows that
     * aren't provably unequal to the LHS; if so, the result is UNKNOWN.
     * Otherwise, the result is FALSE.
     */
    if (node->hashnulls == NULL)
    {
        ExecClearTuple(slot);
        return BoolGetDatum(false);
    }
    if (slotAllNulls(slot))
    {
        ExecClearTuple(slot);
        *isNull = true;
        return BoolGetDatum(false);
    }
    /* Scan partly-null table first, since more likely to get a match */
    if (node->havenullrows &&
        findPartialMatch(node->hashnulls, slot, node->cur_eq_funcs))
    {
        ExecClearTuple(slot);
        *isNull = true;
        return BoolGetDatum(false);
    }
    if (node->havehashrows &&
        findPartialMatch(node->hashtable, slot, node->cur_eq_funcs))
    {
        ExecClearTuple(slot);
        *isNull = true;
        return BoolGetDatum(false);
    }
    ExecClearTuple(slot);
    return BoolGetDatum(false);
}

/*
 * ExecScanSubPlan: default case where we have to rescan subplan each time
 */
static Datum
ExecScanSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull)
{
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
    PlanState  *planstate = node->planstate;
    SubLinkType subLinkType = subplan->subLinkType;
    MemoryContext oldcontext;
    TupleTableSlot *slot;
    Datum       result;
    bool        found = false;  /* TRUE if got at least one subplan tuple */
    ListCell   *pvar;
    ListCell   *l;
    ArrayBuildState *astate = NULL;

    /*
     * We are probably in a short-lived expression-evaluation context. Switch
     * to the per-query context for manipulating the child plan's chgParam,
     * calling ExecProcNode on it, etc.
     */
    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);

    /*
     * Set Params of this plan from parent plan correlation values. (Any
     * calculation we have to do is done in the parent econtext, since the
     * Param values don't need to have per-query lifetime.)
     */
    Assert(list_length(subplan->parParam) == list_length(node->args));

    forboth(l, subplan->parParam, pvar, node->args)
    {
        int         paramid = lfirst_int(l);
        ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

        prm->value = ExecEvalExprSwitchContext((ExprState *) lfirst(pvar),
                                               econtext,
                                               &(prm->isnull),
                                               NULL);
        planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
    }

    /*
     * Now that we've set up its parameters, we can reset the subplan.
     */
    ExecReScan(planstate);

    /*
     * For all sublink types except EXPR_SUBLINK and ARRAY_SUBLINK, the result
     * is boolean as are the results of the combining operators. We combine
     * results across tuples (if the subplan produces more than one) using OR
     * semantics for ANY_SUBLINK or AND semantics for ALL_SUBLINK.
     * (ROWCOMPARE_SUBLINK doesn't allow multiple tuples from the subplan.)
     * NULL results from the combining operators are handled according to the
     * usual SQL semantics for OR and AND.  The result for no input tuples is
     * FALSE for ANY_SUBLINK, TRUE for ALL_SUBLINK, NULL for
     * ROWCOMPARE_SUBLINK.
     *
     * For EXPR_SUBLINK we require the subplan to produce no more than one
     * tuple, else an error is raised.  If zero tuples are produced, we return
     * NULL.  Assuming we get a tuple, we just use its first column (there can
     * be only one non-junk column in this case).
     *
     * For ARRAY_SUBLINK we allow the subplan to produce any number of tuples,
     * and form an array of the first column's values.  Note in particular
     * that we produce a zero-element array if no tuples are produced (this is
     * a change from pre-8.3 behavior of returning NULL).
     */
    result = BoolGetDatum(subLinkType == ALL_SUBLINK);
    *isNull = false;

    for (slot = ExecProcNode(planstate);
         !TupIsNull(slot);
         slot = ExecProcNode(planstate))
    {
        TupleDesc   tdesc = slot->tts_tupleDescriptor;
        Datum       rowresult;
        bool        rownull;
        int         col;
        ListCell   *plst;

        if (subLinkType == EXISTS_SUBLINK)
        {
            found = true;
            result = BoolGetDatum(true);
            break;
        }

        if (subLinkType == EXPR_SUBLINK)
        {
            /* cannot allow multiple input tuples for EXPR sublink */
            if (found)
                ereport(ERROR,
                        (errcode(ERRCODE_CARDINALITY_VIOLATION),
                         errmsg("more than one row returned by a subquery used as an expression")));
            found = true;

            /*
             * We need to copy the subplan's tuple in case the result is of
             * pass-by-ref type --- our return value will point into this
             * copied tuple!  Can't use the subplan's instance of the tuple
             * since it won't still be valid after next ExecProcNode() call.
             * node->curTuple keeps track of the copied tuple for eventual
             * freeing.
             */
            if (node->curTuple)
                heap_freetuple(node->curTuple);
            node->curTuple = ExecCopySlotTuple(slot);

            result = heap_getattr(node->curTuple, 1, tdesc, isNull);
            /* keep scanning subplan to make sure there's only one tuple */
            continue;
        }

        if (subLinkType == ARRAY_SUBLINK)
        {
            Datum       dvalue;
            bool        disnull;

            found = true;
            /* stash away current value */
            Assert(subplan->firstColType == tdesc->attrs[0]->atttypid);
            dvalue = slot_getattr(slot, 1, &disnull);
            astate = accumArrayResult(astate, dvalue, disnull,
                                      subplan->firstColType, oldcontext);
            /* keep scanning subplan to collect all values */
            continue;
        }

        /* cannot allow multiple input tuples for ROWCOMPARE sublink either */
        if (subLinkType == ROWCOMPARE_SUBLINK && found)
            ereport(ERROR,
                    (errcode(ERRCODE_CARDINALITY_VIOLATION),
                     errmsg("more than one row returned by a subquery used as an expression")));

        found = true;

        /*
         * For ALL, ANY, and ROWCOMPARE sublinks, load up the Params
         * representing the columns of the sub-select, and then evaluate the
         * combining expression.
         */
        col = 1;
        foreach(plst, subplan->paramIds)
        {
            int         paramid = lfirst_int(plst);
            ParamExecData *prmdata;

            prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
            Assert(prmdata->execPlan == NULL);
            prmdata->value = slot_getattr(slot, col, &(prmdata->isnull));
            col++;
        }

        rowresult = ExecEvalExprSwitchContext(node->testexpr, econtext,
                                              &rownull, NULL);

        if (subLinkType == ANY_SUBLINK)
        {
            /* combine across rows per OR semantics */
            if (rownull)
                *isNull = true;
            else if (DatumGetBool(rowresult))
            {
                result = BoolGetDatum(true);
                *isNull = false;
                break;          /* needn't look at any more rows */
            }
        }
        else if (subLinkType == ALL_SUBLINK)
        {
            /* combine across rows per AND semantics */
            if (rownull)
                *isNull = true;
            else if (!DatumGetBool(rowresult))
            {
                result = BoolGetDatum(false);
                *isNull = false;
                break;          /* needn't look at any more rows */
            }
        }
        else
        {
            /* must be ROWCOMPARE_SUBLINK */
            result = rowresult;
            *isNull = rownull;
        }
    }

    MemoryContextSwitchTo(oldcontext);

    if (subLinkType == ARRAY_SUBLINK)
    {
        /* We return the result in the caller's context */
        if (astate != NULL)
            result = makeArrayResult(astate, oldcontext);
        else
            result = PointerGetDatum(construct_empty_array(subplan->firstColType));
    }
    else if (!found)
    {
        /*
         * deal with empty subplan result.  result/isNull were previously
         * initialized correctly for all sublink types except EXPR and
         * ROWCOMPARE; for those, return NULL.
         */
        if (subLinkType == EXPR_SUBLINK ||
            subLinkType == ROWCOMPARE_SUBLINK)
        {
            result = (Datum) 0;
            *isNull = true;
        }
    }

    return result;
}

/*
 * buildSubPlanHash: load hash table by scanning subplan output.
 */
static void
buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
{
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
    PlanState  *planstate = node->planstate;
    int         ncols = list_length(subplan->paramIds);
    ExprContext *innerecontext = node->innerecontext;
    MemoryContext oldcontext;
    long        nbuckets;
    TupleTableSlot *slot;

    Assert(subplan->subLinkType == ANY_SUBLINK);

    /*
     * If we already had any hash tables, destroy 'em; then create empty hash
     * table(s).
     *
     * If we need to distinguish accurately between FALSE and UNKNOWN (i.e.,
     * NULL) results of the IN operation, then we have to store subplan output
     * rows that are partly or wholly NULL.  We store such rows in a separate
     * hash table that we expect will be much smaller than the main table. (We
     * can use hashing to eliminate partly-null rows that are not distinct. We
     * keep them separate to minimize the cost of the inevitable full-table
     * searches; see findPartialMatch.)
     *
     * If it's not necessary to distinguish FALSE and UNKNOWN, then we don't
     * need to store subplan output rows that contain NULL.
     */
    MemoryContextReset(node->hashtablecxt);
    node->hashtable = NULL;
    node->hashnulls = NULL;
    node->havehashrows = false;
    node->havenullrows = false;

    nbuckets = (long) Min(planstate->plan->plan_rows, (double) LONG_MAX);
    if (nbuckets < 1)
        nbuckets = 1;

    node->hashtable = BuildTupleHashTable(ncols,
                                          node->keyColIdx,
                                          node->tab_eq_funcs,
                                          node->tab_hash_funcs,
                                          nbuckets,
                                          sizeof(TupleHashEntryData),
                                          node->hashtablecxt,
                                          node->hashtempcxt);

    if (!subplan->unknownEqFalse)
    {
        if (ncols == 1)
            nbuckets = 1;       /* there can only be one entry */
        else
        {
            nbuckets /= 16;
            if (nbuckets < 1)
                nbuckets = 1;
        }
        node->hashnulls = BuildTupleHashTable(ncols,
                                              node->keyColIdx,
                                              node->tab_eq_funcs,
                                              node->tab_hash_funcs,
                                              nbuckets,
                                              sizeof(TupleHashEntryData),
                                              node->hashtablecxt,
                                              node->hashtempcxt);
    }

    /*
     * We are probably in a short-lived expression-evaluation context. Switch
     * to the per-query context for manipulating the child plan.
     */
    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);

    /*
     * Reset subplan to start.
     */
    ExecReScan(planstate);

    /*
     * Scan the subplan and load the hash table(s).  Note that when there are
     * duplicate rows coming out of the sub-select, only one copy is stored.
     */
    for (slot = ExecProcNode(planstate);
         !TupIsNull(slot);
         slot = ExecProcNode(planstate))
    {
        int         col = 1;
        ListCell   *plst;
        bool        isnew;

        /*
         * Load up the Params representing the raw sub-select outputs, then
         * form the projection tuple to store in the hashtable.
         */
        foreach(plst, subplan->paramIds)
        {
            int         paramid = lfirst_int(plst);
            ParamExecData *prmdata;

            prmdata = &(innerecontext->ecxt_param_exec_vals[paramid]);
            Assert(prmdata->execPlan == NULL);
            prmdata->value = slot_getattr(slot, col,
                                          &(prmdata->isnull));
            col++;
        }
        slot = ExecProject(node->projRight, NULL);

        /*
         * If result contains any nulls, store separately or not at all.
         */
        if (slotNoNulls(slot))
        {
            (void) LookupTupleHashEntry(node->hashtable, slot, &isnew);
            node->havehashrows = true;
        }
        else if (node->hashnulls)
        {
            (void) LookupTupleHashEntry(node->hashnulls, slot, &isnew);
            node->havenullrows = true;
        }

        /*
         * Reset innerecontext after each inner tuple to free any memory used
         * during ExecProject.
         */
        ResetExprContext(innerecontext);
    }

    /*
     * Since the projected tuples are in the sub-query's context and not the
     * main context, we'd better clear the tuple slot before there's any
     * chance of a reset of the sub-query's context.  Else we will have the
     * potential for a double free attempt.  (XXX possibly no longer needed,
     * but can't hurt.)
     */
    ExecClearTuple(node->projRight->pi_slot);

    MemoryContextSwitchTo(oldcontext);
}

/*
 * findPartialMatch: does the hashtable contain an entry that is not
 * provably distinct from the tuple?
 *
 * We have to scan the whole hashtable; we can't usefully use hashkeys
 * to guide probing, since we might get partial matches on tuples with
 * hashkeys quite unrelated to what we'd get from the given tuple.
 *
 * Caller must provide the equality functions to use, since in cross-type
 * cases these are different from the hashtable's internal functions.
 */
static bool
findPartialMatch(TupleHashTable hashtable, TupleTableSlot *slot,
                 FmgrInfo *eqfunctions)
{
    int         numCols = hashtable->numCols;
    AttrNumber *keyColIdx = hashtable->keyColIdx;
    TupleHashIterator hashiter;
    TupleHashEntry entry;

    InitTupleHashIterator(hashtable, &hashiter);
    while ((entry = ScanTupleHashTable(&hashiter)) != NULL)
    {
        ExecStoreMinimalTuple(entry->firstTuple, hashtable->tableslot, false);
        if (!execTuplesUnequal(slot, hashtable->tableslot,
                               numCols, keyColIdx,
                               eqfunctions,
                               hashtable->tempcxt))
        {
            TermTupleHashIterator(&hashiter);
            return true;
        }
    }
    /* No TermTupleHashIterator call needed here */
    return false;
}

/*
 * slotAllNulls: is the slot completely NULL?
 *
 * This does not test for dropped columns, which is OK because we only
 * use it on projected tuples.
 */
static bool
slotAllNulls(TupleTableSlot *slot)
{
    int         ncols = slot->tts_tupleDescriptor->natts;
    int         i;

    for (i = 1; i <= ncols; i++)
    {
        if (!slot_attisnull(slot, i))
            return false;
    }
    return true;
}

/*
 * slotNoNulls: is the slot entirely not NULL?
 *
 * This does not test for dropped columns, which is OK because we only
 * use it on projected tuples.
 */
static bool
slotNoNulls(TupleTableSlot *slot)
{
    int         ncols = slot->tts_tupleDescriptor->natts;
    int         i;

    for (i = 1; i <= ncols; i++)
    {
        if (slot_attisnull(slot, i))
            return false;
    }
    return true;
}

/* ----------------------------------------------------------------
 *      ExecInitSubPlan
 *
 * Create a SubPlanState for a SubPlan; this is the SubPlan-specific part
 * of ExecInitExpr().  We split it out so that it can be used for InitPlans
 * as well as regular SubPlans.  Note that we don't link the SubPlan into
 * the parent's subPlan list, because that shouldn't happen for InitPlans.
 * Instead, ExecInitExpr() does that one part.
 * ----------------------------------------------------------------
 */
SubPlanState *
ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
{
    SubPlanState *sstate = makeNode(SubPlanState);
    EState     *estate = parent->state;

    sstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecSubPlan;
    sstate->xprstate.expr = (Expr *) subplan;

    /* Link the SubPlanState to already-initialized subplan */
    sstate->planstate = (PlanState *) list_nth(estate->es_subplanstates,
                                               subplan->plan_id - 1);

    /* Initialize subexpressions */
    sstate->testexpr = ExecInitExpr((Expr *) subplan->testexpr, parent);
    sstate->args = (List *) ExecInitExpr((Expr *) subplan->args, parent);

    /*
     * initialize my state
     */
    sstate->curTuple = NULL;
    sstate->curArray = PointerGetDatum(NULL);
    sstate->projLeft = NULL;
    sstate->projRight = NULL;
    sstate->hashtable = NULL;
    sstate->hashnulls = NULL;
    sstate->hashtablecxt = NULL;
    sstate->hashtempcxt = NULL;
    sstate->innerecontext = NULL;
    sstate->keyColIdx = NULL;
    sstate->tab_hash_funcs = NULL;
    sstate->tab_eq_funcs = NULL;
    sstate->lhs_hash_funcs = NULL;
    sstate->cur_eq_funcs = NULL;

    /*
     * If this plan is un-correlated or undirect correlated one and want to
     * set params for parent plan then mark parameters as needing evaluation.
     *
     * A CTE subplan's output parameter is never to be evaluated in the normal
     * way, so skip this in that case.
     *
     * Note that in the case of un-correlated subqueries we don't care about
     * setting parent->chgParam here: indices take care about it, for others -
     * it doesn't matter...
     */
    if (subplan->setParam != NIL && subplan->subLinkType != CTE_SUBLINK)
    {
        ListCell   *lst;

        foreach(lst, subplan->setParam)
        {
            int         paramid = lfirst_int(lst);
            ParamExecData *prm = &(estate->es_param_exec_vals[paramid]);

            prm->execPlan = sstate;
        }
    }

    /*
     * If we are going to hash the subquery output, initialize relevant stuff.
     * (We don't create the hashtable until needed, though.)
     */
    if (subplan->useHashTable)
    {
        int         ncols,
                    i;
        TupleDesc   tupDesc;
        TupleTableSlot *slot;
        List       *oplist,
                   *lefttlist,
                   *righttlist,
                   *leftptlist,
                   *rightptlist;
        ListCell   *l;

        /* We need a memory context to hold the hash table(s) */
        sstate->hashtablecxt =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "Subplan HashTable Context",
                                  ALLOCSET_DEFAULT_MINSIZE,
                                  ALLOCSET_DEFAULT_INITSIZE,
                                  ALLOCSET_DEFAULT_MAXSIZE);
        /* and a small one for the hash tables to use as temp storage */
        sstate->hashtempcxt =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "Subplan HashTable Temp Context",
                                  ALLOCSET_SMALL_MINSIZE,
                                  ALLOCSET_SMALL_INITSIZE,
                                  ALLOCSET_SMALL_MAXSIZE);
        /* and a short-lived exprcontext for function evaluation */
        sstate->innerecontext = CreateExprContext(estate);
        /* Silly little array of column numbers 1..n */
        ncols = list_length(subplan->paramIds);
        sstate->keyColIdx = (AttrNumber *) palloc(ncols * sizeof(AttrNumber));
        for (i = 0; i < ncols; i++)
            sstate->keyColIdx[i] = i + 1;

        /*
         * We use ExecProject to evaluate the lefthand and righthand
         * expression lists and form tuples.  (You might think that we could
         * use the sub-select's output tuples directly, but that is not the
         * case if we had to insert any run-time coercions of the sub-select's
         * output datatypes; anyway this avoids storing any resjunk columns
         * that might be in the sub-select's output.) Run through the
         * combining expressions to build tlists for the lefthand and
         * righthand sides.  We need both the ExprState list (for ExecProject)
         * and the underlying parse Exprs (for ExecTypeFromTL).
         *
         * We also extract the combining operators themselves to initialize
         * the equality and hashing functions for the hash tables.
         */
        if (IsA(sstate->testexpr->expr, OpExpr))
        {
            /* single combining operator */
            oplist = list_make1(sstate->testexpr);
        }
        else if (and_clause((Node *) sstate->testexpr->expr))
        {
            /* multiple combining operators */
            Assert(IsA(sstate->testexpr, BoolExprState));
            oplist = ((BoolExprState *) sstate->testexpr)->args;
        }
        else
        {
            /* shouldn't see anything else in a hashable subplan */
            elog(ERROR, "unrecognized testexpr type: %d",
                 (int) nodeTag(sstate->testexpr->expr));
            oplist = NIL;       /* keep compiler quiet */
        }
        Assert(list_length(oplist) == ncols);

        lefttlist = righttlist = NIL;
        leftptlist = rightptlist = NIL;
        sstate->tab_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        sstate->tab_eq_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        sstate->lhs_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        sstate->cur_eq_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        i = 1;
        foreach(l, oplist)
        {
            FuncExprState *fstate = (FuncExprState *) lfirst(l);
            OpExpr     *opexpr = (OpExpr *) fstate->xprstate.expr;
            ExprState  *exstate;
            Expr       *expr;
            TargetEntry *tle;
            GenericExprState *tlestate;
            Oid         rhs_eq_oper;
            Oid         left_hashfn;
            Oid         right_hashfn;

            Assert(IsA(fstate, FuncExprState));
            Assert(IsA(opexpr, OpExpr));
            Assert(list_length(fstate->args) == 2);

            /* Process lefthand argument */
            exstate = (ExprState *) linitial(fstate->args);
            expr = exstate->expr;
            tle = makeTargetEntry(expr,
                                  i,
                                  NULL,
                                  false);
            tlestate = makeNode(GenericExprState);
            tlestate->xprstate.expr = (Expr *) tle;
            tlestate->xprstate.evalfunc = NULL;
            tlestate->arg = exstate;
            lefttlist = lappend(lefttlist, tlestate);
            leftptlist = lappend(leftptlist, tle);

            /* Process righthand argument */
            exstate = (ExprState *) lsecond(fstate->args);
            expr = exstate->expr;
            tle = makeTargetEntry(expr,
                                  i,
                                  NULL,
                                  false);
            tlestate = makeNode(GenericExprState);
            tlestate->xprstate.expr = (Expr *) tle;
            tlestate->xprstate.evalfunc = NULL;
            tlestate->arg = exstate;
            righttlist = lappend(righttlist, tlestate);
            rightptlist = lappend(rightptlist, tle);

            /* Lookup the equality function (potentially cross-type) */
            fmgr_info(opexpr->opfuncid, &sstate->cur_eq_funcs[i - 1]);
            fmgr_info_set_expr((Node *) opexpr, &sstate->cur_eq_funcs[i - 1]);

            /* Look up the equality function for the RHS type */
            if (!get_compatible_hash_operators(opexpr->opno,
                                               NULL, &rhs_eq_oper))
                elog(ERROR, "could not find compatible hash operator for operator %u",
                     opexpr->opno);
            fmgr_info(get_opcode(rhs_eq_oper), &sstate->tab_eq_funcs[i - 1]);

            /* Lookup the associated hash functions */
            if (!get_op_hash_functions(opexpr->opno,
                                       &left_hashfn, &right_hashfn))
                elog(ERROR, "could not find hash function for hash operator %u",
                     opexpr->opno);
            fmgr_info(left_hashfn, &sstate->lhs_hash_funcs[i - 1]);
            fmgr_info(right_hashfn, &sstate->tab_hash_funcs[i - 1]);

            i++;
        }

        /*
         * Construct tupdescs, slots and projection nodes for left and right
         * sides.  The lefthand expressions will be evaluated in the parent
         * plan node's exprcontext, which we don't have access to here.
         * Fortunately we can just pass NULL for now and fill it in later
         * (hack alert!).  The righthand expressions will be evaluated in our
         * own innerecontext.
         */
        tupDesc = ExecTypeFromTL(leftptlist, false);
        slot = ExecInitExtraTupleSlot(estate);
        ExecSetSlotDescriptor(slot, tupDesc);
        sstate->projLeft = ExecBuildProjectionInfo(lefttlist,
                                                   NULL,
                                                   slot,
                                                   NULL);

        tupDesc = ExecTypeFromTL(rightptlist, false);
        slot = ExecInitExtraTupleSlot(estate);
        ExecSetSlotDescriptor(slot, tupDesc);
        sstate->projRight = ExecBuildProjectionInfo(righttlist,
                                                    sstate->innerecontext,
                                                    slot,
                                                    NULL);
    }

    return sstate;
}

/* ----------------------------------------------------------------
 *      ExecSetParamPlan
 *
 *      Executes an InitPlan subplan and sets its output parameters.
 *
 * This is called from ExecEvalParamExec() when the value of a PARAM_EXEC
 * parameter is requested and the param's execPlan field is set (indicating
 * that the param has not yet been evaluated).  This allows lazy evaluation
 * of initplans: we don't run the subplan until/unless we need its output.
 * Note that this routine MUST clear the execPlan fields of the plan's
 * output parameters after evaluating them!
 * ----------------------------------------------------------------
 */
void
ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
{
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
    PlanState  *planstate = node->planstate;
    SubLinkType subLinkType = subplan->subLinkType;
    MemoryContext oldcontext;
    TupleTableSlot *slot;
    ListCell   *l;
    bool        found = false;
    ArrayBuildState *astate = NULL;

    if (subLinkType == ANY_SUBLINK ||
        subLinkType == ALL_SUBLINK)
        elog(ERROR, "ANY/ALL subselect unsupported as initplan");
    if (subLinkType == CTE_SUBLINK)
        elog(ERROR, "CTE subplans should not be executed via ExecSetParamPlan");

    /*
     * Must switch to per-query memory context.
     */
    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_query_memory);

    /*
     * Run the plan.  (If it needs to be rescanned, the first ExecProcNode
     * call will take care of that.)
     */
    for (slot = ExecProcNode(planstate);
         !TupIsNull(slot);
         slot = ExecProcNode(planstate))
    {
        TupleDesc   tdesc = slot->tts_tupleDescriptor;
        int         i = 1;

        if (subLinkType == EXISTS_SUBLINK)
        {
            /* There can be only one setParam... */
            int         paramid = linitial_int(subplan->setParam);
            ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

            prm->execPlan = NULL;
            prm->value = BoolGetDatum(true);
            prm->isnull = false;
            found = true;
            break;
        }

        if (subLinkType == ARRAY_SUBLINK)
        {
            Datum       dvalue;
            bool        disnull;

            found = true;
            /* stash away current value */
            Assert(subplan->firstColType == tdesc->attrs[0]->atttypid);
            dvalue = slot_getattr(slot, 1, &disnull);
            astate = accumArrayResult(astate, dvalue, disnull,
                                      subplan->firstColType, oldcontext);
            /* keep scanning subplan to collect all values */
            continue;
        }

        if (found &&
            (subLinkType == EXPR_SUBLINK ||
             subLinkType == ROWCOMPARE_SUBLINK))
            ereport(ERROR,
                    (errcode(ERRCODE_CARDINALITY_VIOLATION),
                     errmsg("more than one row returned by a subquery used as an expression")));

        found = true;

        /*
         * We need to copy the subplan's tuple into our own context, in case
         * any of the params are pass-by-ref type --- the pointers stored in
         * the param structs will point at this copied tuple! node->curTuple
         * keeps track of the copied tuple for eventual freeing.
         */
        if (node->curTuple)
            heap_freetuple(node->curTuple);
        node->curTuple = ExecCopySlotTuple(slot);

        /*
         * Now set all the setParam params from the columns of the tuple
         */
        foreach(l, subplan->setParam)
        {
            int         paramid = lfirst_int(l);
            ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

            prm->execPlan = NULL;
            prm->value = heap_getattr(node->curTuple, i, tdesc,
                                      &(prm->isnull));
            i++;
        }
    }

    if (subLinkType == ARRAY_SUBLINK)
    {
        /* There can be only one setParam... */
        int         paramid = linitial_int(subplan->setParam);
        ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

        /*
         * We build the result array in query context so it won't disappear;
         * to avoid leaking memory across repeated calls, we have to remember
         * the latest value, much as for curTuple above.
         */
        if (node->curArray != PointerGetDatum(NULL))
            pfree(DatumGetPointer(node->curArray));
        if (astate != NULL)
            node->curArray = makeArrayResult(astate,
                                             econtext->ecxt_per_query_memory);
        else
        {
            MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
            node->curArray = PointerGetDatum(construct_empty_array(subplan->firstColType));
        }
        prm->execPlan = NULL;
        prm->value = node->curArray;
        prm->isnull = false;
    }
    else if (!found)
    {
        if (subLinkType == EXISTS_SUBLINK)
        {
            /* There can be only one setParam... */
            int         paramid = linitial_int(subplan->setParam);
            ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

            prm->execPlan = NULL;
            prm->value = BoolGetDatum(false);
            prm->isnull = false;
        }
        else
        {
            foreach(l, subplan->setParam)
            {
                int         paramid = lfirst_int(l);
                ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);

                prm->execPlan = NULL;
                prm->value = (Datum) 0;
                prm->isnull = true;
            }
        }
    }

    MemoryContextSwitchTo(oldcontext);
}

/*
 * Mark an initplan as needing recalculation
 */
void
ExecReScanSetParamPlan(SubPlanState *node, PlanState *parent)
{
    PlanState  *planstate = node->planstate;
    SubPlan    *subplan = (SubPlan *) node->xprstate.expr;
    EState     *estate = parent->state;
    ListCell   *l;

    /* sanity checks */
    if (subplan->parParam != NIL)
        elog(ERROR, "direct correlated subquery unsupported as initplan");
    if (subplan->setParam == NIL)
        elog(ERROR, "setParam list of initplan is empty");
    if (bms_is_empty(planstate->plan->extParam))
        elog(ERROR, "extParam set of initplan is empty");

    /*
     * Don't actually re-scan: it'll happen inside ExecSetParamPlan if needed.
     */

    /*
     * Mark this subplan's output parameters as needing recalculation.
     *
     * CTE subplans are never executed via parameter recalculation; instead
     * they get run when called by nodeCtescan.c.  So don't mark the output
     * parameter of a CTE subplan as dirty, but do set the chgParam bit for it
     * so that dependent plan nodes will get told to rescan.
     */
    foreach(l, subplan->setParam)
    {
        int         paramid = lfirst_int(l);
        ParamExecData *prm = &(estate->es_param_exec_vals[paramid]);

        if (subplan->subLinkType != CTE_SUBLINK)
            prm->execPlan = node;

        parent->chgParam = bms_add_member(parent->chgParam, paramid);
    }
}


/*
 * ExecInitAlternativeSubPlan
 *
 * Initialize for execution of one of a set of alternative subplans.
 */
AlternativeSubPlanState *
ExecInitAlternativeSubPlan(AlternativeSubPlan *asplan, PlanState *parent)
{
    AlternativeSubPlanState *asstate = makeNode(AlternativeSubPlanState);
    double      num_calls;
    SubPlan    *subplan1;
    SubPlan    *subplan2;
    Cost        cost1;
    Cost        cost2;

    asstate->xprstate.evalfunc = (ExprStateEvalFunc) ExecAlternativeSubPlan;
    asstate->xprstate.expr = (Expr *) asplan;

    /*
     * Initialize subplans.  (Can we get away with only initializing the one
     * we're going to use?)
     */
    asstate->subplans = (List *) ExecInitExpr((Expr *) asplan->subplans,
                                              parent);

    /*
     * Select the one to be used.  For this, we need an estimate of the number
     * of executions of the subplan.  We use the number of output rows
     * expected from the parent plan node.  This is a good estimate if we are
     * in the parent's targetlist, and an underestimate (but probably not by
     * more than a factor of 2) if we are in the qual.
     */
    num_calls = parent->plan->plan_rows;

    /*
     * The planner saved enough info so that we don't have to work very hard
     * to estimate the total cost, given the number-of-calls estimate.
     */
    Assert(list_length(asplan->subplans) == 2);
    subplan1 = (SubPlan *) linitial(asplan->subplans);
    subplan2 = (SubPlan *) lsecond(asplan->subplans);

    cost1 = subplan1->startup_cost + num_calls * subplan1->per_call_cost;
    cost2 = subplan2->startup_cost + num_calls * subplan2->per_call_cost;

    if (cost1 < cost2)
        asstate->active = 0;
    else
        asstate->active = 1;

    return asstate;
}

/*
 * ExecAlternativeSubPlan
 *
 * Execute one of a set of alternative subplans.
 *
 * Note: in future we might consider changing to different subplans on the
 * fly, in case the original rowcount estimate turns out to be way off.
 */
static Datum
ExecAlternativeSubPlan(AlternativeSubPlanState *node,
                       ExprContext *econtext,
                       bool *isNull,
                       ExprDoneCond *isDone)
{
    /* Just pass control to the active subplan */
    SubPlanState *activesp = (SubPlanState *) list_nth(node->subplans,
                                                       node->active);

    Assert(IsA(activesp, SubPlanState));

    return ExecSubPlan(activesp,
                       econtext,
                       isNull,
                       isDone);
}