nodeSubplan.c

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/*-------------------------------------------------------------------------
 *
 * nodeSubplan.c
 *    routines to support sub-selects appearing in expressions
 *
 * This module is concerned with executing SubPlan expression nodes, which
 * should not be confused with sub-SELECTs appearing in FROM.  SubPlans are
 * divided into "initplans", which are those that need only one evaluation per
 * query (among other restrictions, this requires that they don't use any
 * direct correlation variables from the parent plan level), and "regular"
 * subplans, which are re-evaluated every time their result is required.
 *
 *
 * Portions Copyright (c) 1996-2026, 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 "access/htup_details.h"
#include "executor/executor.h"
#include "executor/nodeSubplan.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "utils/array.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
 
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
 *
 * This is the main entry point for execution of a regular SubPlan.
 * ----------------------------------------------------------------
 */
Datum
ExecSubPlan(SubPlanState *node,
            ExprContext *econtext,
            bool *isNull)
{
    SubPlan    *subplan = node->subplan;
    EState     *estate = node->planstate->state;
    ScanDirection dir = estate->es_direction;
    Datum       retval;
 
    CHECK_FOR_INTERRUPTS();
 
    /* Set non-null as default */
    *isNull = false;
 
    /* Sanity checks */
    if (subplan->subLinkType == CTE_SUBLINK)
        elog(ERROR, "CTE subplans should not be executed via ExecSubPlan");
    if (subplan->setParam != NIL && subplan->subLinkType != MULTIEXPR_SUBLINK)
        elog(ERROR, "cannot set parent params from subquery");
 
    /* Force forward-scan mode for evaluation */
    estate->es_direction = ForwardScanDirection;
 
    /* Select appropriate evaluation strategy */
    if (subplan->useHashTable)
        retval = ExecHashSubPlan(node, econtext, isNull);
    else
        retval = ExecScanSubPlan(node, econtext, isNull);
 
    /* restore scan direction */
    estate->es_direction = dir;
 
    return retval;
}
 
/*
 * ExecHashSubPlan: store subselect result in an in-memory hash table
 */
static Datum
ExecHashSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull)
{
    bool        result = false;
    SubPlan    *subplan = node->subplan;
    PlanState  *planstate = node->planstate;
    TupleTableSlot *slot;
 
    /* Shouldn't have any direct correlation Vars */
    if (subplan->parParam != NIL || subplan->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);
 
    /*
     * 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_comp,
                               node->lhs_hash_expr) != NULL)
            result = true;
        else if (node->havenullrows &&
                 findPartialMatch(node->hashnulls, slot, node->cur_eq_funcs))
            *isNull = true;
    }
 
    /*
     * 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.
     */
    else if (node->hashnulls == NULL)
         /* just return FALSE */ ;
    else if (slotAllNulls(slot))
        *isNull = true;
    /* Scan partly-null table first, since more likely to get a match */
    else if (node->havenullrows &&
             findPartialMatch(node->hashnulls, slot, node->cur_eq_funcs))
        *isNull = true;
    else if (node->havehashrows &&
             findPartialMatch(node->hashtable, slot, node->cur_eq_funcs))
        *isNull = true;
 
    /*
     * 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.
     */
    ExecClearTuple(slot);
 
    /* Also must reset the innerecontext after each hashtable lookup. */
    ResetExprContext(node->innerecontext);
 
    return BoolGetDatum(result);
}
 
/*
 * ExecScanSubPlan: default case where we have to rescan subplan each time
 */
static Datum
ExecScanSubPlan(SubPlanState *node,
                ExprContext *econtext,
                bool *isNull)
{
    SubPlan    *subplan = node->subplan;
    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   *l;
    ArrayBuildStateAny *astate = NULL;
 
    /* Initialize ArrayBuildStateAny in caller's context, if needed */
    if (subLinkType == ARRAY_SUBLINK)
        astate = initArrayResultAny(subplan->firstColType,
                                    CurrentMemoryContext, true);
 
    /*
     * 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);
 
    /*
     * We rely on the caller to evaluate plan correlation values, if
     * necessary. However we still need to record the fact that the values
     * (might have) changed, otherwise the ExecReScan() below won't know that
     * nodes need to be rescanned.
     */
    foreach(l, subplan->parParam)
    {
        int         paramid = lfirst_int(l);
 
        planstate->chgParam = bms_add_member(planstate->chgParam, paramid);
    }
 
    /* with that done, 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 MULTIEXPR_SUBLINK, we push the per-column subplan outputs out to
     * the setParams and then return a dummy false value.  There must not be
     * multiple tuples returned from the subplan; if zero tuples are produced,
     * set the setParams to NULL.
     *
     * 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 = ExecCopySlotHeapTuple(slot);
 
            result = heap_getattr(node->curTuple, 1, tdesc, isNull);
            /* keep scanning subplan to make sure there's only one tuple */
            continue;
        }
 
        if (subLinkType == MULTIEXPR_SUBLINK)
        {
            /* cannot allow multiple input tuples for MULTIEXPR 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 any result is of
             * pass-by-ref type --- our output values 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 = ExecCopySlotHeapTuple(slot);
 
            /*
             * Now set all the setParam params from the columns of the tuple
             */
            col = 1;
            foreach(plst, subplan->setParam)
            {
                int         paramid = lfirst_int(plst);
                ParamExecData *prmdata;
 
                prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
                Assert(prmdata->execPlan == NULL);
                prmdata->value = heap_getattr(node->curTuple, col, tdesc,
                                              &(prmdata->isnull));
                col++;
            }
 
            /* 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 == TupleDescAttr(tdesc, 0)->atttypid);
            dvalue = slot_getattr(slot, 1, &disnull);
            astate = accumArrayResultAny(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);
 
        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 */
        result = makeArrayResultAny(astate, oldcontext, true);
    }
    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;
        }
        else if (subLinkType == MULTIEXPR_SUBLINK)
        {
            /* We don't care about function result, but set the setParams */
            foreach(l, subplan->setParam)
            {
                int         paramid = lfirst_int(l);
                ParamExecData *prmdata;
 
                prmdata = &(econtext->ecxt_param_exec_vals[paramid]);
                Assert(prmdata->execPlan == NULL);
                prmdata->value = (Datum) 0;
                prmdata->isnull = true;
            }
        }
    }
 
    return result;
}
 
/*
 * buildSubPlanHash: load hash table by scanning subplan output.
 */
static void
buildSubPlanHash(SubPlanState *node, ExprContext *econtext)
{
    SubPlan    *subplan = node->subplan;
    PlanState  *planstate = node->planstate;
    int         ncols = node->numCols;
    ExprContext *innerecontext = node->innerecontext;
    MemoryContext oldcontext;
    double      nentries;
    TupleTableSlot *slot;
 
    Assert(subplan->subLinkType == ANY_SUBLINK);
 
    /*
     * If we already had any hash tables, reset 'em; otherwise 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.
     *
     * Because the input slot for each hash table is always the slot resulting
     * from an ExecProject(), we can use TTSOpsVirtual for the input ops. This
     * saves a needless fetch inner op step for the hashing ExprState created
     * in BuildTupleHashTable().
     */
    node->havehashrows = false;
    node->havenullrows = false;
 
    nentries = planstate->plan->plan_rows;
 
    if (node->hashtable)
        ResetTupleHashTable(node->hashtable);
    else
        node->hashtable = BuildTupleHashTable(node->parent,
                                              node->descRight,
                                              &TTSOpsVirtual,
                                              ncols,
                                              node->keyColIdx,
                                              node->tab_eq_funcoids,
                                              node->tab_hash_funcs,
                                              node->tab_collations,
                                              nentries,
                                              0,    /* no additional data */
                                              node->planstate->state->es_query_cxt,
                                              node->tuplesContext,
                                              innerecontext->ecxt_per_tuple_memory,
                                              false);
 
    if (!subplan->unknownEqFalse)
    {
        if (ncols == 1)
            nentries = 1;       /* there can only be one entry */
        else
        {
            nentries /= 16;
            if (nentries < 1)
                nentries = 1;
        }
 
        if (node->hashnulls)
            ResetTupleHashTable(node->hashnulls);
        else
            node->hashnulls = BuildTupleHashTable(node->parent,
                                                  node->descRight,
                                                  &TTSOpsVirtual,
                                                  ncols,
                                                  node->keyColIdx,
                                                  node->tab_eq_funcoids,
                                                  node->tab_hash_funcs,
                                                  node->tab_collations,
                                                  nentries,
                                                  0,    /* no additional data */
                                                  node->planstate->state->es_query_cxt,
                                                  node->tuplesContext,
                                                  innerecontext->ecxt_per_tuple_memory,
                                                  false);
    }
    else
        node->hashnulls = NULL;
 
    /*
     * 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);
 
        /*
         * If result contains any nulls, store separately or not at all.
         */
        if (slotNoNulls(slot))
        {
            (void) LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
            node->havehashrows = true;
        }
        else if (node->hashnulls)
        {
            (void) LookupTupleHashEntry(node->hashnulls, slot, &isnew, NULL);
            node->havenullrows = true;
        }
 
        /*
         * Reset innerecontext after each inner tuple to free any memory used
         * during ExecProject and hashtable lookup.
         */
        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_state.resultslot);
 
    MemoryContextSwitchTo(oldcontext);
}
 
/* Planner support routine to estimate space needed for hash table(s) */
Size
EstimateSubplanHashTableSpace(double nentries,
                              Size tupleWidth,
                              bool unknownEqFalse)
{
    Size        tab1space,
                tab2space;
 
    /* Estimate size of main hashtable */
    tab1space = EstimateTupleHashTableSpace(nentries,
                                            tupleWidth,
                                            0 /* no additional data */ );
 
    /* Give up if that's already too big */
    if (tab1space >= SIZE_MAX)
        return tab1space;
 
    /* Done if we don't need a hashnulls table */
    if (unknownEqFalse)
        return tab1space;
 
    /*
     * Adjust the rowcount estimate in the same way that buildSubPlanHash
     * will, except that we don't bother with the special case for a single
     * hash column.  (We skip that detail because it'd be notationally painful
     * for our caller to provide the column count, and this table has
     * relatively little impact on the total estimate anyway.)
     */
    nentries /= 16;
    if (nentries < 1)
        nentries = 1;
 
    /*
     * It might be sane to also reduce the tupleWidth, but on the other hand
     * we are not accounting for the space taken by the tuples' null bitmaps.
     * Leave it alone for now.
     */
    tab2space = EstimateTupleHashTableSpace(nentries,
                                            tupleWidth,
                                            0 /* no additional data */ );
 
    /* Guard against overflow */
    if (tab2space >= SIZE_MAX - tab1space)
        return SIZE_MAX;
 
    return tab1space + tab2space;
}
 
/*
 * execTuplesUnequal
 *      Return true if two tuples are definitely unequal in the indicated
 *      fields.
 *
 * Nulls are neither equal nor unequal to anything else.  A true result
 * is obtained only if there are non-null fields that compare not-equal.
 *
 * slot1, slot2: the tuples to compare (must have same columns!)
 * numCols: the number of attributes to be examined
 * matchColIdx: array of attribute column numbers
 * eqFunctions: array of fmgr lookup info for the equality functions to use
 * evalContext: short-term memory context for executing the functions
 */
static bool
execTuplesUnequal(TupleTableSlot *slot1,
                  TupleTableSlot *slot2,
                  int numCols,
                  AttrNumber *matchColIdx,
                  FmgrInfo *eqfunctions,
                  const Oid *collations,
                  MemoryContext evalContext)
{
    MemoryContext oldContext;
    bool        result;
    int         i;
 
    /* Reset and switch into the temp context. */
    MemoryContextReset(evalContext);
    oldContext = MemoryContextSwitchTo(evalContext);
 
    /*
     * We cannot report a match without checking all the fields, but we can
     * report a non-match as soon as we find unequal fields.  So, start
     * comparing at the last field (least significant sort key). That's the
     * most likely to be different if we are dealing with sorted input.
     */
    result = false;
 
    for (i = numCols; --i >= 0;)
    {
        AttrNumber  att = matchColIdx[i];
        Datum       attr1,
                    attr2;
        bool        isNull1,
                    isNull2;
 
        attr1 = slot_getattr(slot1, att, &isNull1);
 
        if (isNull1)
            continue;           /* can't prove anything here */
 
        attr2 = slot_getattr(slot2, att, &isNull2);
 
        if (isNull2)
            continue;           /* can't prove anything here */
 
        /* Apply the type-specific equality function */
        if (!DatumGetBool(FunctionCall2Coll(&eqfunctions[i],
                                            collations[i],
                                            attr1, attr2)))
        {
            result = true;      /* they are unequal */
            break;
        }
    }
 
    MemoryContextSwitchTo(oldContext);
 
    return result;
}
 
/*
 * 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(hashtable, &hashiter)) != NULL)
    {
        CHECK_FOR_INTERRUPTS();
 
        ExecStoreMinimalTuple(TupleHashEntryGetTuple(entry), hashtable->tableslot, false);
        if (!execTuplesUnequal(slot, hashtable->tableslot,
                               numCols, keyColIdx,
                               eqfunctions,
                               hashtable->tab_collations,
                               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.
 *
 * We also rely on ExecInitExpr(), more precisely ExecInitSubPlanExpr(), to
 * evaluate input parameters, as that allows them to be evaluated as part of
 * the expression referencing the SubPlan.
 * ----------------------------------------------------------------
 */
SubPlanState *
ExecInitSubPlan(SubPlan *subplan, PlanState *parent)
{
    SubPlanState *sstate = makeNode(SubPlanState);
    EState     *estate = parent->state;
 
    sstate->subplan = subplan;
 
    /* Link the SubPlanState to already-initialized subplan */
    sstate->planstate = (PlanState *) list_nth(estate->es_subplanstates,
                                               subplan->plan_id - 1);
 
    /*
     * This check can fail if the planner mistakenly puts a parallel-unsafe
     * subplan into a parallelized subquery; see ExecSerializePlan.
     */
    if (sstate->planstate == NULL)
        elog(ERROR, "subplan \"%s\" was not initialized",
             subplan->plan_name);
 
    /* Link to parent's state, too */
    sstate->parent = parent;
 
    /* Initialize subexpressions */
    sstate->testexpr = ExecInitExpr((Expr *) subplan->testexpr, parent);
 
    /*
     * initialize my state
     */
    sstate->curTuple = NULL;
    sstate->curArray = PointerGetDatum(NULL);
    sstate->projLeft = NULL;
    sstate->projRight = NULL;
    sstate->hashtable = NULL;
    sstate->hashnulls = NULL;
    sstate->tuplesContext = NULL;
    sstate->innerecontext = NULL;
    sstate->keyColIdx = NULL;
    sstate->tab_eq_funcoids = NULL;
    sstate->tab_hash_funcs = NULL;
    sstate->tab_collations = NULL;
    sstate->cur_eq_funcs = NULL;
 
    /*
     * If this is an initplan, it has output parameters that the parent plan
     * will use, so mark those parameters as needing evaluation.  We don't
     * actually run the subplan until we first need one of its outputs.
     *
     * A CTE subplan's output parameter is never to be evaluated in the normal
     * way, so skip this in that case.
     *
     * Note that we don't set parent->chgParam here: the parent plan hasn't
     * been run yet, so no need to force it to re-run.
     */
    if (subplan->setParam != NIL && subplan->parParam == 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   tupDescLeft;
        TupleDesc   tupDescRight;
        Oid        *cross_eq_funcoids;
        TupleTableSlot *slot;
        FmgrInfo   *lhs_hash_funcs;
        List       *oplist,
                   *lefttlist,
                   *righttlist;
        ListCell   *l;
 
        /* We need a memory context to hold the hash table(s)' tuples */
        sstate->tuplesContext =
            BumpContextCreate(CurrentMemoryContext,
                              "SubPlan hashed tuples",
                              ALLOCSET_DEFAULT_SIZES);
        /* and a short-lived exprcontext for function evaluation */
        sstate->innerecontext = CreateExprContext(estate);
 
        /*
         * 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 also extract the combining operators themselves to initialize
         * the equality and hashing functions for the hash tables.
         */
        if (IsA(subplan->testexpr, OpExpr))
        {
            /* single combining operator */
            oplist = list_make1(subplan->testexpr);
        }
        else if (is_andclause(subplan->testexpr))
        {
            /* multiple combining operators */
            oplist = castNode(BoolExpr, subplan->testexpr)->args;
        }
        else
        {
            /* shouldn't see anything else in a hashable subplan */
            elog(ERROR, "unrecognized testexpr type: %d",
                 (int) nodeTag(subplan->testexpr));
            oplist = NIL;       /* keep compiler quiet */
        }
        ncols = list_length(oplist);
 
        lefttlist = righttlist = NIL;
        sstate->numCols = ncols;
        sstate->keyColIdx = (AttrNumber *) palloc(ncols * sizeof(AttrNumber));
        sstate->tab_eq_funcoids = (Oid *) palloc(ncols * sizeof(Oid));
        sstate->tab_collations = (Oid *) palloc(ncols * sizeof(Oid));
        sstate->tab_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        lhs_hash_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        sstate->cur_eq_funcs = (FmgrInfo *) palloc(ncols * sizeof(FmgrInfo));
        /* we'll need the cross-type equality fns below, but not in sstate */
        cross_eq_funcoids = (Oid *) palloc(ncols * sizeof(Oid));
 
        i = 1;
        foreach(l, oplist)
        {
            OpExpr     *opexpr = lfirst_node(OpExpr, l);
            Expr       *expr;
            TargetEntry *tle;
            Oid         rhs_eq_oper;
            Oid         left_hashfn;
            Oid         right_hashfn;
 
            Assert(list_length(opexpr->args) == 2);
 
            /* Process lefthand argument */
            expr = (Expr *) linitial(opexpr->args);
            tle = makeTargetEntry(expr,
                                  i,
                                  NULL,
                                  false);
            lefttlist = lappend(lefttlist, tle);
 
            /* Process righthand argument */
            expr = (Expr *) lsecond(opexpr->args);
            tle = makeTargetEntry(expr,
                                  i,
                                  NULL,
                                  false);
            righttlist = lappend(righttlist, tle);
 
            /* Lookup the equality function (potentially cross-type) */
            cross_eq_funcoids[i - 1] = opexpr->opfuncid;
            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);
            sstate->tab_eq_funcoids[i - 1] = get_opcode(rhs_eq_oper);
 
            /* 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, &lhs_hash_funcs[i - 1]);
            fmgr_info(right_hashfn, &sstate->tab_hash_funcs[i - 1]);
 
            /* Set collation */
            sstate->tab_collations[i - 1] = opexpr->inputcollid;
 
            /* keyColIdx is just column numbers 1..n */
            sstate->keyColIdx[i - 1] = i;
 
            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.
         */
        tupDescLeft = ExecTypeFromTL(lefttlist);
        slot = ExecInitExtraTupleSlot(estate, tupDescLeft, &TTSOpsVirtual);
        sstate->projLeft = ExecBuildProjectionInfo(lefttlist,
                                                   NULL,
                                                   slot,
                                                   parent,
                                                   NULL);
 
        sstate->descRight = tupDescRight = ExecTypeFromTL(righttlist);
        slot = ExecInitExtraTupleSlot(estate, tupDescRight, &TTSOpsVirtual);
        sstate->projRight = ExecBuildProjectionInfo(righttlist,
                                                    sstate->innerecontext,
                                                    slot,
                                                    sstate->planstate,
                                                    NULL);
 
        /* Build the ExprState for generating hash values */
        sstate->lhs_hash_expr = ExecBuildHash32FromAttrs(tupDescLeft,
                                                         &TTSOpsVirtual,
                                                         lhs_hash_funcs,
                                                         sstate->tab_collations,
                                                         sstate->numCols,
                                                         sstate->keyColIdx,
                                                         parent,
                                                         0);
 
        /*
         * Create comparator for lookups of rows in the table (potentially
         * cross-type comparisons).
         */
        sstate->cur_eq_comp = ExecBuildGroupingEqual(tupDescLeft, tupDescRight,
                                                     &TTSOpsVirtual, &TTSOpsMinimalTuple,
                                                     ncols,
                                                     sstate->keyColIdx,
                                                     cross_eq_funcoids,
                                                     sstate->tab_collations,
                                                     parent);
    }
 
    return sstate;
}
 
/* ----------------------------------------------------------------
 *      ExecSetParamPlan
 *
 *      Executes a 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!
 *
 * The results of this function are stored in the EState associated with the
 * ExprContext (particularly, its ecxt_param_exec_vals); any pass-by-ref
 * result Datums are allocated in the EState's per-query memory.  The passed
 * econtext can be any ExprContext belonging to that EState; which one is
 * important only to the extent that the ExprContext's per-tuple memory
 * context is used to evaluate any parameters passed down to the subplan.
 * (Thus in principle, the shorter-lived the ExprContext the better, since
 * that data isn't needed after we return.  In practice, because initplan
 * parameters are never more complex than Vars, Aggrefs, etc, evaluating them
 * currently never leaks any memory anyway.)
 * ----------------------------------------------------------------
 */
void
ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
{
    SubPlan    *subplan = node->subplan;
    PlanState  *planstate = node->planstate;
    SubLinkType subLinkType = subplan->subLinkType;
    EState     *estate = planstate->state;
    ScanDirection dir = estate->es_direction;
    MemoryContext oldcontext;
    TupleTableSlot *slot;
    ListCell   *l;
    bool        found = false;
    ArrayBuildStateAny *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");
    if (subplan->parParam || subplan->args)
        elog(ERROR, "correlated subplans should not be executed via ExecSetParamPlan");
 
    /*
     * Enforce forward scan direction regardless of caller. It's hard but not
     * impossible to get here in backward scan, so make it work anyway.
     */
    estate->es_direction = ForwardScanDirection;
 
    /* Initialize ArrayBuildStateAny in caller's context, if needed */
    if (subLinkType == ARRAY_SUBLINK)
        astate = initArrayResultAny(subplan->firstColType,
                                    CurrentMemoryContext, true);
 
    /*
     * 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 == TupleDescAttr(tdesc, 0)->atttypid);
            dvalue = slot_getattr(slot, 1, &disnull);
            astate = accumArrayResultAny(astate, dvalue, disnull,
                                         subplan->firstColType, oldcontext);
            /* keep scanning subplan to collect all values */
            continue;
        }
 
        if (found &&
            (subLinkType == EXPR_SUBLINK ||
             subLinkType == MULTIEXPR_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 = ExecCopySlotHeapTuple(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));
        node->curArray = makeArrayResultAny(astate,
                                            econtext->ecxt_per_query_memory,
                                            true);
        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
        {
            /* For other sublink types, set all the output params to NULL */
            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);
 
    /* restore scan direction */
    estate->es_direction = dir;
}
 
/*
 * ExecSetParamPlanMulti
 *
 * Apply ExecSetParamPlan to evaluate any not-yet-evaluated initplan output
 * parameters whose ParamIDs are listed in "params".  Any listed params that
 * are not initplan outputs are ignored.
 *
 * As with ExecSetParamPlan, any ExprContext belonging to the current EState
 * can be used, but in principle a shorter-lived ExprContext is better than a
 * longer-lived one.
 */
void
ExecSetParamPlanMulti(const Bitmapset *params, ExprContext *econtext)
{
    int         paramid;
 
    paramid = -1;
    while ((paramid = bms_next_member(params, paramid)) >= 0)
    {
        ParamExecData *prm = &(econtext->ecxt_param_exec_vals[paramid]);
 
        if (prm->execPlan != NULL)
        {
            /* Parameter not evaluated yet, so go do it */
            ExecSetParamPlan(prm->execPlan, econtext);
            /* ExecSetParamPlan should have processed this param... */
            Assert(prm->execPlan == NULL);
        }
    }
}
 
/*
 * Mark an initplan as needing recalculation
 */
void
ExecReScanSetParamPlan(SubPlanState *node, PlanState *parent)
{
    PlanState  *planstate = node->planstate;
    SubPlan    *subplan = node->subplan;
    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);
    }
}