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Sourcecode: postgresql-8.4 version File versions

nodeSubplan.c

/*-------------------------------------------------------------------------
 *
 * nodeSubplan.c
 *      routines to support subselects
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/executor/nodeSubplan.c,v 1.99 2009/06/11 14:48:57 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 *     INTERFACE ROUTINES
 *          ExecSubPlan  - process a subselect
 *          ExecInitSubPlan - initialize a subselect
 */
#include "postgres.h"

#include <math.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);
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;
      ExprContext *innerecontext = node->innerecontext;
      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.
       */

      /*
       * Since the hashtable routines will use innerecontext's per-tuple memory
       * as working memory, be sure to reset it for each tuple.
       */
      ResetExprContext(innerecontext);

      /*
       * 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))
            {
                  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))
      {
            ExecClearTuple(slot);
            *isNull = true;
            return BoolGetDatum(false);
      }
      if (node->havehashrows &&
            findPartialMatch(node->hashtable, slot))
      {
            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, NULL);

      /*
       * 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 tempcxt = innerecontext->ecxt_per_tuple_memory;
      MemoryContext oldcontext;
      int               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->tablecxt);
      node->hashtable = NULL;
      node->hashnulls = NULL;
      node->havehashrows = false;
      node->havenullrows = false;

      nbuckets = (int) ceil(planstate->plan->plan_rows);
      if (nbuckets < 1)
            nbuckets = 1;

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

      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->tablecxt,
                                                                    tempcxt);
      }

      /*
       * 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, NULL);

      /*
       * 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
             * in hash computation or comparison routines.
             */
            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.
 */
static bool
findPartialMatch(TupleHashTable hashtable, TupleTableSlot *slot)
{
      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,
                                             hashtable->cur_eq_funcs,
                                             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->projLeft = NULL;
      sstate->projRight = NULL;
      sstate->hashtable = NULL;
      sstate->hashnulls = NULL;
      sstate->tablecxt = 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;
            TupleTable  tupTable;
            TupleTableSlot *slot;
            List     *oplist,
                           *lefttlist,
                           *righttlist,
                           *leftptlist,
                           *rightptlist;
            ListCell   *l;

            /* We need a memory context to hold the hash table(s) */
            sstate->tablecxt =
                  AllocSetContextCreate(CurrentMemoryContext,
                                                  "Subplan HashTable Context",
                                                  ALLOCSET_DEFAULT_MINSIZE,
                                                  ALLOCSET_DEFAULT_INITSIZE,
                                                  ALLOCSET_DEFAULT_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]);
                  sstate->cur_eq_funcs[i - 1].fn_expr = (Node *) opexpr;

                  /* 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++;
            }

            /*
             * Create a tupletable to hold these tuples.  (Note: we never bother
             * to free the tupletable explicitly; that's okay because it will
             * never store raw disk tuples that might have associated buffer pins.
             * The only resource involved is memory, which will be cleaned up by
             * freeing the query context.)
             */
            tupTable = ExecCreateTupleTable(2);

            /*
             * 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 = ExecAllocTableSlot(tupTable);
            ExecSetSlotDescriptor(slot, tupDesc);
            sstate->projLeft = ExecBuildProjectionInfo(lefttlist,
                                                                           NULL,
                                                                           slot,
                                                                           NULL);

            tupDesc = ExecTypeFromTL(rightptlist, false);
            slot = ExecAllocTableSlot(tupTable);
            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 ExecEvalParam() 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]);

            prm->execPlan = NULL;
            /* We build the result in query context so it won't disappear */
            if (astate != NULL)
                  prm->value = makeArrayResult(astate,
                                                             econtext->ecxt_per_query_memory);
            else
            {
                  MemoryContextSwitchTo(econtext->ecxt_per_query_memory);
                  prm->value = PointerGetDatum(construct_empty_array(subplan->firstColType));
            }
            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);
}

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