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Sourcecode: postgresql-8.4 version File versions

planner.c

/*-------------------------------------------------------------------------
 *
 * planner.c
 *      The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.256 2009/06/11 14:48:59 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>

#include "catalog/pg_operator.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/subselect.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


/* GUC parameter */
double            cursor_tuple_fraction = DEFAULT_CURSOR_TUPLE_FRACTION;

/* Hook for plugins to get control in planner() */
planner_hook_type planner_hook = NULL;


/* Expression kind codes for preprocess_expression */
#define EXPRKIND_QUAL         0
#define EXPRKIND_TARGET       1
#define EXPRKIND_RTFUNC       2
#define EXPRKIND_VALUES       3
#define EXPRKIND_LIMIT        4
#define EXPRKIND_APPINFO      5


static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
static Plan *inheritance_planner(PlannerInfo *root);
static Plan *grouping_planner(PlannerInfo *root, double tuple_fraction);
static bool is_dummy_plan(Plan *plan);
static double preprocess_limit(PlannerInfo *root,
                         double tuple_fraction,
                         int64 *offset_est, int64 *count_est);
static void preprocess_groupclause(PlannerInfo *root);
static bool choose_hashed_grouping(PlannerInfo *root,
                                 double tuple_fraction, double limit_tuples,
                                 Path *cheapest_path, Path *sorted_path,
                                 double dNumGroups, AggClauseCounts *agg_counts);
static bool choose_hashed_distinct(PlannerInfo *root,
                                 Plan *input_plan, List *input_pathkeys,
                                 double tuple_fraction, double limit_tuples,
                                 double dNumDistinctRows);
static List *make_subplanTargetList(PlannerInfo *root, List *tlist,
                                 AttrNumber **groupColIdx, bool *need_tlist_eval);
static void locate_grouping_columns(PlannerInfo *root,
                                    List *tlist,
                                    List *sub_tlist,
                                    AttrNumber *groupColIdx);
static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
static List *select_active_windows(PlannerInfo *root, WindowFuncLists *wflists);
static List *add_volatile_sort_exprs(List *window_tlist, List *tlist,
                                    List *activeWindows);
static List *make_pathkeys_for_window(PlannerInfo *root, WindowClause *wc,
                                     List *tlist, bool canonicalize);
static void get_column_info_for_window(PlannerInfo *root, WindowClause *wc,
                                       List *tlist,
                                       int numSortCols, AttrNumber *sortColIdx,
                                       int *partNumCols,
                                       AttrNumber **partColIdx,
                                       Oid **partOperators,
                                       int *ordNumCols,
                                       AttrNumber **ordColIdx,
                                       Oid **ordOperators);


/*****************************************************************************
 *
 *       Query optimizer entry point
 *
 * To support loadable plugins that monitor or modify planner behavior,
 * we provide a hook variable that lets a plugin get control before and
 * after the standard planning process.  The plugin would normally call
 * standard_planner().
 *
 * Note to plugin authors: standard_planner() scribbles on its Query input,
 * so you'd better copy that data structure if you want to plan more than once.
 *
 *****************************************************************************/
PlannedStmt *
planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
{
      PlannedStmt *result;

      if (planner_hook)
            result = (*planner_hook) (parse, cursorOptions, boundParams);
      else
            result = standard_planner(parse, cursorOptions, boundParams);
      return result;
}

PlannedStmt *
standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
{
      PlannedStmt *result;
      PlannerGlobal *glob;
      double            tuple_fraction;
      PlannerInfo *root;
      Plan     *top_plan;
      ListCell   *lp,
                     *lr;

      /* Cursor options may come from caller or from DECLARE CURSOR stmt */
      if (parse->utilityStmt &&
            IsA(parse->utilityStmt, DeclareCursorStmt))
            cursorOptions |= ((DeclareCursorStmt *) parse->utilityStmt)->options;

      /*
       * Set up global state for this planner invocation.  This data is needed
       * across all levels of sub-Query that might exist in the given command,
       * so we keep it in a separate struct that's linked to by each per-Query
       * PlannerInfo.
       */
      glob = makeNode(PlannerGlobal);

      glob->boundParams = boundParams;
      glob->paramlist = NIL;
      glob->subplans = NIL;
      glob->subrtables = NIL;
      glob->rewindPlanIDs = NULL;
      glob->finalrtable = NIL;
      glob->relationOids = NIL;
      glob->invalItems = NIL;
      glob->lastPHId = 0;
      glob->transientPlan = false;

      /* Determine what fraction of the plan is likely to be scanned */
      if (cursorOptions & CURSOR_OPT_FAST_PLAN)
      {
            /*
             * We have no real idea how many tuples the user will ultimately FETCH
             * from a cursor, but it is often the case that he doesn't want 'em
             * all, or would prefer a fast-start plan anyway so that he can
             * process some of the tuples sooner.  Use a GUC parameter to decide
             * what fraction to optimize for.
             */
            tuple_fraction = cursor_tuple_fraction;

            /*
             * We document cursor_tuple_fraction as simply being a fraction, which
             * means the edge cases 0 and 1 have to be treated specially here.      We
             * convert 1 to 0 ("all the tuples") and 0 to a very small fraction.
             */
            if (tuple_fraction >= 1.0)
                  tuple_fraction = 0.0;
            else if (tuple_fraction <= 0.0)
                  tuple_fraction = 1e-10;
      }
      else
      {
            /* Default assumption is we need all the tuples */
            tuple_fraction = 0.0;
      }

      /* primary planning entry point (may recurse for subqueries) */
      top_plan = subquery_planner(glob, parse, NULL,
                                                false, tuple_fraction, &root);

      /*
       * If creating a plan for a scrollable cursor, make sure it can run
       * backwards on demand.  Add a Material node at the top at need.
       */
      if (cursorOptions & CURSOR_OPT_SCROLL)
      {
            if (!ExecSupportsBackwardScan(top_plan))
                  top_plan = materialize_finished_plan(top_plan);
      }

      /* final cleanup of the plan */
      Assert(glob->finalrtable == NIL);
      top_plan = set_plan_references(glob, top_plan, root->parse->rtable);
      /* ... and the subplans (both regular subplans and initplans) */
      Assert(list_length(glob->subplans) == list_length(glob->subrtables));
      forboth(lp, glob->subplans, lr, glob->subrtables)
      {
            Plan     *subplan = (Plan *) lfirst(lp);
            List     *subrtable = (List *) lfirst(lr);

            lfirst(lp) = set_plan_references(glob, subplan, subrtable);
      }

      /* build the PlannedStmt result */
      result = makeNode(PlannedStmt);

      result->commandType = parse->commandType;
      result->canSetTag = parse->canSetTag;
      result->transientPlan = glob->transientPlan;
      result->planTree = top_plan;
      result->rtable = glob->finalrtable;
      result->resultRelations = root->resultRelations;
      result->utilityStmt = parse->utilityStmt;
      result->intoClause = parse->intoClause;
      result->subplans = glob->subplans;
      result->rewindPlanIDs = glob->rewindPlanIDs;
      result->returningLists = root->returningLists;
      result->rowMarks = parse->rowMarks;
      result->relationOids = glob->relationOids;
      result->invalItems = glob->invalItems;
      result->nParamExec = list_length(glob->paramlist);

      return result;
}


/*--------------------
 * subquery_planner
 *      Invokes the planner on a subquery.  We recurse to here for each
 *      sub-SELECT found in the query tree.
 *
 * glob is the global state for the current planner run.
 * parse is the querytree produced by the parser & rewriter.
 * parent_root is the immediate parent Query's info (NULL at the top level).
 * hasRecursion is true if this is a recursive WITH query.
 * tuple_fraction is the fraction of tuples we expect will be retrieved.
 * tuple_fraction is interpreted as explained for grouping_planner, below.
 *
 * If subroot isn't NULL, we pass back the query's final PlannerInfo struct;
 * among other things this tells the output sort ordering of the plan.
 *
 * Basically, this routine does the stuff that should only be done once
 * per Query object.  It then calls grouping_planner.  At one time,
 * grouping_planner could be invoked recursively on the same Query object;
 * that's not currently true, but we keep the separation between the two
 * routines anyway, in case we need it again someday.
 *
 * subquery_planner will be called recursively to handle sub-Query nodes
 * found within the query's expressions and rangetable.
 *
 * Returns a query plan.
 *--------------------
 */
Plan *
subquery_planner(PlannerGlobal *glob, Query *parse,
                         PlannerInfo *parent_root,
                         bool hasRecursion, double tuple_fraction,
                         PlannerInfo **subroot)
{
      int               num_old_subplans = list_length(glob->subplans);
      PlannerInfo *root;
      Plan     *plan;
      List     *newHaving;
      bool        hasOuterJoins;
      ListCell   *l;

      /* Create a PlannerInfo data structure for this subquery */
      root = makeNode(PlannerInfo);
      root->parse = parse;
      root->glob = glob;
      root->query_level = parent_root ? parent_root->query_level + 1 : 1;
      root->parent_root = parent_root;
      root->planner_cxt = CurrentMemoryContext;
      root->init_plans = NIL;
      root->cte_plan_ids = NIL;
      root->eq_classes = NIL;
      root->append_rel_list = NIL;

      root->hasRecursion = hasRecursion;
      if (hasRecursion)
            root->wt_param_id = SS_assign_worktable_param(root);
      else
            root->wt_param_id = -1;
      root->non_recursive_plan = NULL;

      /*
       * If there is a WITH list, process each WITH query and build an initplan
       * SubPlan structure for it.
       */
      if (parse->cteList)
            SS_process_ctes(root);

      /*
       * Look for ANY and EXISTS SubLinks in WHERE and JOIN/ON clauses, and try
       * to transform them into joins.  Note that this step does not descend
       * into subqueries; if we pull up any subqueries below, their SubLinks are
       * processed just before pulling them up.
       */
      if (parse->hasSubLinks)
            pull_up_sublinks(root);

      /*
       * Scan the rangetable for set-returning functions, and inline them if
       * possible (producing subqueries that might get pulled up next).
       * Recursion issues here are handled in the same way as for SubLinks.
       */
      inline_set_returning_functions(root);

      /*
       * Check to see if any subqueries in the rangetable can be merged into
       * this query.
       */
      parse->jointree = (FromExpr *)
            pull_up_subqueries(root, (Node *) parse->jointree, NULL, NULL);

      /*
       * Detect whether any rangetable entries are RTE_JOIN kind; if not, we can
       * avoid the expense of doing flatten_join_alias_vars().  Also check for
       * outer joins --- if none, we can skip reduce_outer_joins(). This must be
       * done after we have done pull_up_subqueries, of course.
       */
      root->hasJoinRTEs = false;
      hasOuterJoins = false;
      foreach(l, parse->rtable)
      {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

            if (rte->rtekind == RTE_JOIN)
            {
                  root->hasJoinRTEs = true;
                  if (IS_OUTER_JOIN(rte->jointype))
                  {
                        hasOuterJoins = true;
                        /* Can quit scanning once we find an outer join */
                        break;
                  }
            }
      }

      /*
       * Expand any rangetable entries that are inheritance sets into "append
       * relations".  This can add entries to the rangetable, but they must be
       * plain base relations not joins, so it's OK (and marginally more
       * efficient) to do it after checking for join RTEs.  We must do it after
       * pulling up subqueries, else we'd fail to handle inherited tables in
       * subqueries.
       */
      expand_inherited_tables(root);

      /*
       * Set hasHavingQual to remember if HAVING clause is present.  Needed
       * because preprocess_expression will reduce a constant-true condition to
       * an empty qual list ... but "HAVING TRUE" is not a semantic no-op.
       */
      root->hasHavingQual = (parse->havingQual != NULL);

      /* Clear this flag; might get set in distribute_qual_to_rels */
      root->hasPseudoConstantQuals = false;

      /*
       * Do expression preprocessing on targetlist and quals.
       */
      parse->targetList = (List *)
            preprocess_expression(root, (Node *) parse->targetList,
                                            EXPRKIND_TARGET);

      parse->returningList = (List *)
            preprocess_expression(root, (Node *) parse->returningList,
                                            EXPRKIND_TARGET);

      preprocess_qual_conditions(root, (Node *) parse->jointree);

      parse->havingQual = preprocess_expression(root, parse->havingQual,
                                                                    EXPRKIND_QUAL);

      parse->limitOffset = preprocess_expression(root, parse->limitOffset,
                                                                     EXPRKIND_LIMIT);
      parse->limitCount = preprocess_expression(root, parse->limitCount,
                                                                    EXPRKIND_LIMIT);

      root->append_rel_list = (List *)
            preprocess_expression(root, (Node *) root->append_rel_list,
                                            EXPRKIND_APPINFO);

      /* Also need to preprocess expressions for function and values RTEs */
      foreach(l, parse->rtable)
      {
            RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

            if (rte->rtekind == RTE_FUNCTION)
                  rte->funcexpr = preprocess_expression(root, rte->funcexpr,
                                                                          EXPRKIND_RTFUNC);
            else if (rte->rtekind == RTE_VALUES)
                  rte->values_lists = (List *)
                        preprocess_expression(root, (Node *) rte->values_lists,
                                                        EXPRKIND_VALUES);
      }

      /*
       * In some cases we may want to transfer a HAVING clause into WHERE. We
       * cannot do so if the HAVING clause contains aggregates (obviously) or
       * volatile functions (since a HAVING clause is supposed to be executed
       * only once per group).  Also, it may be that the clause is so expensive
       * to execute that we're better off doing it only once per group, despite
       * the loss of selectivity.  This is hard to estimate short of doing the
       * entire planning process twice, so we use a heuristic: clauses
       * containing subplans are left in HAVING.      Otherwise, we move or copy the
       * HAVING clause into WHERE, in hopes of eliminating tuples before
       * aggregation instead of after.
       *
       * If the query has explicit grouping then we can simply move such a
       * clause into WHERE; any group that fails the clause will not be in the
       * output because none of its tuples will reach the grouping or
       * aggregation stage.  Otherwise we must have a degenerate (variable-free)
       * HAVING clause, which we put in WHERE so that query_planner() can use it
       * in a gating Result node, but also keep in HAVING to ensure that we
       * don't emit a bogus aggregated row. (This could be done better, but it
       * seems not worth optimizing.)
       *
       * Note that both havingQual and parse->jointree->quals are in
       * implicitly-ANDed-list form at this point, even though they are declared
       * as Node *.
       */
      newHaving = NIL;
      foreach(l, (List *) parse->havingQual)
      {
            Node     *havingclause = (Node *) lfirst(l);

            if (contain_agg_clause(havingclause) ||
                  contain_volatile_functions(havingclause) ||
                  contain_subplans(havingclause))
            {
                  /* keep it in HAVING */
                  newHaving = lappend(newHaving, havingclause);
            }
            else if (parse->groupClause)
            {
                  /* move it to WHERE */
                  parse->jointree->quals = (Node *)
                        lappend((List *) parse->jointree->quals, havingclause);
            }
            else
            {
                  /* put a copy in WHERE, keep it in HAVING */
                  parse->jointree->quals = (Node *)
                        lappend((List *) parse->jointree->quals,
                                    copyObject(havingclause));
                  newHaving = lappend(newHaving, havingclause);
            }
      }
      parse->havingQual = (Node *) newHaving;

      /*
       * If we have any outer joins, try to reduce them to plain inner joins.
       * This step is most easily done after we've done expression
       * preprocessing.
       */
      if (hasOuterJoins)
            reduce_outer_joins(root);

      /*
       * Do the main planning.  If we have an inherited target relation, that
       * needs special processing, else go straight to grouping_planner.
       */
      if (parse->resultRelation &&
            rt_fetch(parse->resultRelation, parse->rtable)->inh)
            plan = inheritance_planner(root);
      else
            plan = grouping_planner(root, tuple_fraction);

      /*
       * If any subplans were generated, or if we're inside a subplan, build
       * initPlan list and extParam/allParam sets for plan nodes, and attach the
       * initPlans to the top plan node.
       */
      if (list_length(glob->subplans) != num_old_subplans ||
            root->query_level > 1)
            SS_finalize_plan(root, plan, true);

      /* Return internal info if caller wants it */
      if (subroot)
            *subroot = root;

      return plan;
}

/*
 * preprocess_expression
 *          Do subquery_planner's preprocessing work for an expression,
 *          which can be a targetlist, a WHERE clause (including JOIN/ON
 *          conditions), or a HAVING clause.
 */
static Node *
preprocess_expression(PlannerInfo *root, Node *expr, int kind)
{
      /*
       * Fall out quickly if expression is empty.  This occurs often enough to
       * be worth checking.  Note that null->null is the correct conversion for
       * implicit-AND result format, too.
       */
      if (expr == NULL)
            return NULL;

      /*
       * If the query has any join RTEs, replace join alias variables with
       * base-relation variables. We must do this before sublink processing,
       * else sublinks expanded out from join aliases wouldn't get processed. We
       * can skip it in VALUES lists, however, since they can't contain any Vars
       * at all.
       */
      if (root->hasJoinRTEs && kind != EXPRKIND_VALUES)
            expr = flatten_join_alias_vars(root, expr);

      /*
       * Simplify constant expressions.
       *
       * Note: one essential effect here is to insert the current actual values
       * of any default arguments for functions.      To ensure that happens, we
       * *must* process all expressions here.  Previous PG versions sometimes
       * skipped const-simplification if it didn't seem worth the trouble, but
       * we can't do that anymore.
       *
       * Note: this also flattens nested AND and OR expressions into N-argument
       * form.  All processing of a qual expression after this point must be
       * careful to maintain AND/OR flatness --- that is, do not generate a tree
       * with AND directly under AND, nor OR directly under OR.
       */
      expr = eval_const_expressions(root, expr);

      /*
       * If it's a qual or havingQual, canonicalize it.
       */
      if (kind == EXPRKIND_QUAL)
      {
            expr = (Node *) canonicalize_qual((Expr *) expr);

#ifdef OPTIMIZER_DEBUG
            printf("After canonicalize_qual()\n");
            pprint(expr);
#endif
      }

      /* Expand SubLinks to SubPlans */
      if (root->parse->hasSubLinks)
            expr = SS_process_sublinks(root, expr, (kind == EXPRKIND_QUAL));

      /*
       * XXX do not insert anything here unless you have grokked the comments in
       * SS_replace_correlation_vars ...
       */

      /* Replace uplevel vars with Param nodes (this IS possible in VALUES) */
      if (root->query_level > 1)
            expr = SS_replace_correlation_vars(root, expr);

      /*
       * If it's a qual or havingQual, convert it to implicit-AND format. (We
       * don't want to do this before eval_const_expressions, since the latter
       * would be unable to simplify a top-level AND correctly. Also,
       * SS_process_sublinks expects explicit-AND format.)
       */
      if (kind == EXPRKIND_QUAL)
            expr = (Node *) make_ands_implicit((Expr *) expr);

      return expr;
}

/*
 * preprocess_qual_conditions
 *          Recursively scan the query's jointree and do subquery_planner's
 *          preprocessing work on each qual condition found therein.
 */
static void
preprocess_qual_conditions(PlannerInfo *root, Node *jtnode)
{
      if (jtnode == NULL)
            return;
      if (IsA(jtnode, RangeTblRef))
      {
            /* nothing to do here */
      }
      else if (IsA(jtnode, FromExpr))
      {
            FromExpr   *f = (FromExpr *) jtnode;
            ListCell   *l;

            foreach(l, f->fromlist)
                  preprocess_qual_conditions(root, lfirst(l));

            f->quals = preprocess_expression(root, f->quals, EXPRKIND_QUAL);
      }
      else if (IsA(jtnode, JoinExpr))
      {
            JoinExpr   *j = (JoinExpr *) jtnode;

            preprocess_qual_conditions(root, j->larg);
            preprocess_qual_conditions(root, j->rarg);

            j->quals = preprocess_expression(root, j->quals, EXPRKIND_QUAL);
      }
      else
            elog(ERROR, "unrecognized node type: %d",
                   (int) nodeTag(jtnode));
}

/*
 * inheritance_planner
 *      Generate a plan in the case where the result relation is an
 *      inheritance set.
 *
 * We have to handle this case differently from cases where a source relation
 * is an inheritance set. Source inheritance is expanded at the bottom of the
 * plan tree (see allpaths.c), but target inheritance has to be expanded at
 * the top.  The reason is that for UPDATE, each target relation needs a
 * different targetlist matching its own column set.  Also, for both UPDATE
 * and DELETE, the executor needs the Append plan node at the top, else it
 * can't keep track of which table is the current target table.  Fortunately,
 * the UPDATE/DELETE target can never be the nullable side of an outer join,
 * so it's OK to generate the plan this way.
 *
 * Returns a query plan.
 */
static Plan *
inheritance_planner(PlannerInfo *root)
{
      Query    *parse = root->parse;
      int               parentRTindex = parse->resultRelation;
      List     *subplans = NIL;
      List     *resultRelations = NIL;
      List     *returningLists = NIL;
      List     *rtable = NIL;
      List     *tlist = NIL;
      PlannerInfo subroot;
      ListCell   *l;

      foreach(l, root->append_rel_list)
      {
            AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
            Plan     *subplan;

            /* append_rel_list contains all append rels; ignore others */
            if (appinfo->parent_relid != parentRTindex)
                  continue;

            /*
             * Generate modified query with this rel as target.
             */
            memcpy(&subroot, root, sizeof(PlannerInfo));
            subroot.parse = (Query *)
                  adjust_appendrel_attrs((Node *) parse,
                                                   appinfo);
            subroot.returningLists = NIL;
            subroot.init_plans = NIL;
            /* We needn't modify the child's append_rel_list */
            /* There shouldn't be any OJ info to translate, as yet */
            Assert(subroot.join_info_list == NIL);
            /* and we haven't created PlaceHolderInfos, either */
            Assert(subroot.placeholder_list == NIL);

            /* Generate plan */
            subplan = grouping_planner(&subroot, 0.0 /* retrieve all tuples */ );

            /*
             * If this child rel was excluded by constraint exclusion, exclude it
             * from the plan.
             */
            if (is_dummy_plan(subplan))
                  continue;

            /* Save rtable and tlist from first rel for use below */
            if (subplans == NIL)
            {
                  rtable = subroot.parse->rtable;
                  tlist = subplan->targetlist;
            }

            subplans = lappend(subplans, subplan);

            /* Make sure any initplans from this rel get into the outer list */
            root->init_plans = list_concat(root->init_plans, subroot.init_plans);

            /* Build target-relations list for the executor */
            resultRelations = lappend_int(resultRelations, appinfo->child_relid);

            /* Build list of per-relation RETURNING targetlists */
            if (parse->returningList)
            {
                  Assert(list_length(subroot.returningLists) == 1);
                  returningLists = list_concat(returningLists,
                                                             subroot.returningLists);
            }
      }

      root->resultRelations = resultRelations;
      root->returningLists = returningLists;

      /* Mark result as unordered (probably unnecessary) */
      root->query_pathkeys = NIL;

      /*
       * If we managed to exclude every child rel, return a dummy plan
       */
      if (subplans == NIL)
      {
            root->resultRelations = list_make1_int(parentRTindex);
            /* although dummy, it must have a valid tlist for executor */
            tlist = preprocess_targetlist(root, parse->targetList);
            return (Plan *) make_result(root,
                                                      tlist,
                                                      (Node *) list_make1(makeBoolConst(false,
                                                                                                        false)),
                                                      NULL);
      }

      /*
       * Planning might have modified the rangetable, due to changes of the
       * Query structures inside subquery RTEs.  We have to ensure that this
       * gets propagated back to the master copy.  But can't do this until we
       * are done planning, because all the calls to grouping_planner need
       * virgin sub-Queries to work from.  (We are effectively assuming that
       * sub-Queries will get planned identically each time, or at least that
       * the impacts on their rangetables will be the same each time.)
       *
       * XXX should clean this up someday
       */
      parse->rtable = rtable;

      /* Suppress Append if there's only one surviving child rel */
      if (list_length(subplans) == 1)
            return (Plan *) linitial(subplans);

      return (Plan *) make_append(subplans, true, tlist);
}

/*--------------------
 * grouping_planner
 *      Perform planning steps related to grouping, aggregation, etc.
 *      This primarily means adding top-level processing to the basic
 *      query plan produced by query_planner.
 *
 * tuple_fraction is the fraction of tuples we expect will be retrieved
 *
 * tuple_fraction is interpreted as follows:
 *      0: expect all tuples to be retrieved (normal case)
 *      0 < tuple_fraction < 1: expect the given fraction of tuples available
 *          from the plan to be retrieved
 *      tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 *          expected to be retrieved (ie, a LIMIT specification)
 *
 * Returns a query plan.  Also, root->query_pathkeys is returned as the
 * actual output ordering of the plan (in pathkey format).
 *--------------------
 */
static Plan *
grouping_planner(PlannerInfo *root, double tuple_fraction)
{
      Query    *parse = root->parse;
      List     *tlist = parse->targetList;
      int64       offset_est = 0;
      int64       count_est = 0;
      double            limit_tuples = -1.0;
      Plan     *result_plan;
      List     *current_pathkeys;
      double            dNumGroups = 0;

      /* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
      if (parse->limitCount || parse->limitOffset)
      {
            tuple_fraction = preprocess_limit(root, tuple_fraction,
                                                              &offset_est, &count_est);

            /*
             * If we have a known LIMIT, and don't have an unknown OFFSET, we can
             * estimate the effects of using a bounded sort.
             */
            if (count_est > 0 && offset_est >= 0)
                  limit_tuples = (double) count_est + (double) offset_est;
      }

      if (parse->setOperations)
      {
            List     *set_sortclauses;

            /*
             * If there's a top-level ORDER BY, assume we have to fetch all the
             * tuples.  This might be too simplistic given all the hackery below
             * to possibly avoid the sort; but the odds of accurate estimates here
             * are pretty low anyway.
             */
            if (parse->sortClause)
                  tuple_fraction = 0.0;

            /*
             * Construct the plan for set operations.  The result will not need
             * any work except perhaps a top-level sort and/or LIMIT.  Note that
             * any special work for recursive unions is the responsibility of
             * plan_set_operations.
             */
            result_plan = plan_set_operations(root, tuple_fraction,
                                                              &set_sortclauses);

            /*
             * Calculate pathkeys representing the sort order (if any) of the set
             * operation's result.  We have to do this before overwriting the sort
             * key information...
             */
            current_pathkeys = make_pathkeys_for_sortclauses(root,
                                                                                     set_sortclauses,
                                                                               result_plan->targetlist,
                                                                                     true);

            /*
             * We should not need to call preprocess_targetlist, since we must be
             * in a SELECT query node.    Instead, use the targetlist returned by
             * plan_set_operations (since this tells whether it returned any
             * resjunk columns!), and transfer any sort key information from the
             * original tlist.
             */
            Assert(parse->commandType == CMD_SELECT);

            tlist = postprocess_setop_tlist(copyObject(result_plan->targetlist),
                                                            tlist);

            /*
             * Can't handle FOR UPDATE/SHARE here (parser should have checked
             * already, but let's make sure).
             */
            if (parse->rowMarks)
                  ereport(ERROR,
                              (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                               errmsg("SELECT FOR UPDATE/SHARE is not allowed with UNION/INTERSECT/EXCEPT")));

            /*
             * Calculate pathkeys that represent result ordering requirements
             */
            Assert(parse->distinctClause == NIL);
            root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
                                                                                          parse->sortClause,
                                                                                          tlist,
                                                                                          true);
      }
      else
      {
            /* No set operations, do regular planning */
            List     *sub_tlist;
            AttrNumber *groupColIdx = NULL;
            bool        need_tlist_eval = true;
            QualCost    tlist_cost;
            Path     *cheapest_path;
            Path     *sorted_path;
            Path     *best_path;
            long        numGroups = 0;
            AggClauseCounts agg_counts;
            int               numGroupCols;
            bool        use_hashed_grouping = false;
            WindowFuncLists *wflists = NULL;
            List     *activeWindows = NIL;

            MemSet(&agg_counts, 0, sizeof(AggClauseCounts));

            /* A recursive query should always have setOperations */
            Assert(!root->hasRecursion);

            /* Preprocess GROUP BY clause, if any */
            if (parse->groupClause)
                  preprocess_groupclause(root);
            numGroupCols = list_length(parse->groupClause);

            /* Preprocess targetlist */
            tlist = preprocess_targetlist(root, tlist);

            /*
             * Locate any window functions in the tlist.  (We don't need to look
             * anywhere else, since expressions used in ORDER BY will be in there
             * too.)  Note that they could all have been eliminated by constant
             * folding, in which case we don't need to do any more work.
             */
            if (parse->hasWindowFuncs)
            {
                  wflists = find_window_functions((Node *) tlist,
                                                                  list_length(parse->windowClause));
                  if (wflists->numWindowFuncs > 0)
                        activeWindows = select_active_windows(root, wflists);
                  else
                        parse->hasWindowFuncs = false;
            }

            /*
             * Generate appropriate target list for subplan; may be different from
             * tlist if grouping or aggregation is needed.
             */
            sub_tlist = make_subplanTargetList(root, tlist,
                                                               &groupColIdx, &need_tlist_eval);

            /*
             * Calculate pathkeys that represent grouping/ordering requirements.
             * Stash them in PlannerInfo so that query_planner can canonicalize
             * them after EquivalenceClasses have been formed.    The sortClause is
             * certainly sort-able, but GROUP BY and DISTINCT might not be, in
             * which case we just leave their pathkeys empty.
             */
            if (parse->groupClause &&
                  grouping_is_sortable(parse->groupClause))
                  root->group_pathkeys =
                        make_pathkeys_for_sortclauses(root,
                                                                    parse->groupClause,
                                                                    tlist,
                                                                    false);
            else
                  root->group_pathkeys = NIL;

            /* We consider only the first (bottom) window in pathkeys logic */
            if (activeWindows != NIL)
            {
                  WindowClause *wc = (WindowClause *) linitial(activeWindows);

                  root->window_pathkeys = make_pathkeys_for_window(root,
                                                                                           wc,
                                                                                           tlist,
                                                                                           false);
            }
            else
                  root->window_pathkeys = NIL;

            if (parse->distinctClause &&
                  grouping_is_sortable(parse->distinctClause))
                  root->distinct_pathkeys =
                        make_pathkeys_for_sortclauses(root,
                                                                    parse->distinctClause,
                                                                    tlist,
                                                                    false);
            else
                  root->distinct_pathkeys = NIL;

            root->sort_pathkeys =
                  make_pathkeys_for_sortclauses(root,
                                                              parse->sortClause,
                                                              tlist,
                                                              false);

            /*
             * Will need actual number of aggregates for estimating costs.
             *
             * Note: we do not attempt to detect duplicate aggregates here; a
             * somewhat-overestimated count is okay for our present purposes.
             *
             * Note: think not that we can turn off hasAggs if we find no aggs. It
             * is possible for constant-expression simplification to remove all
             * explicit references to aggs, but we still have to follow the
             * aggregate semantics (eg, producing only one output row).
             */
            if (parse->hasAggs)
            {
                  count_agg_clauses((Node *) tlist, &agg_counts);
                  count_agg_clauses(parse->havingQual, &agg_counts);
            }

            /*
             * Figure out whether we want a sorted result from query_planner.
             *
             * If we have a sortable GROUP BY clause, then we want a result sorted
             * properly for grouping.  Otherwise, if we have window functions to
             * evaluate, we try to sort for the first window.  Otherwise, if
             * there's a sortable DISTINCT clause that's more rigorous than the
             * ORDER BY clause, we try to produce output that's sufficiently well
             * sorted for the DISTINCT.  Otherwise, if there is an ORDER BY
             * clause, we want to sort by the ORDER BY clause.
             *
             * Note: if we have both ORDER BY and GROUP BY, and ORDER BY is a
             * superset of GROUP BY, it would be tempting to request sort by ORDER
             * BY --- but that might just leave us failing to exploit an available
             * sort order at all.  Needs more thought.      The choice for DISTINCT
             * versus ORDER BY is much easier, since we know that the parser
             * ensured that one is a superset of the other.
             */
            if (root->group_pathkeys)
                  root->query_pathkeys = root->group_pathkeys;
            else if (root->window_pathkeys)
                  root->query_pathkeys = root->window_pathkeys;
            else if (list_length(root->distinct_pathkeys) >
                         list_length(root->sort_pathkeys))
                  root->query_pathkeys = root->distinct_pathkeys;
            else if (root->sort_pathkeys)
                  root->query_pathkeys = root->sort_pathkeys;
            else
                  root->query_pathkeys = NIL;

            /*
             * Generate the best unsorted and presorted paths for this Query (but
             * note there may not be any presorted path).  query_planner will also
             * estimate the number of groups in the query, and canonicalize all
             * the pathkeys.
             */
            query_planner(root, sub_tlist, tuple_fraction, limit_tuples,
                                &cheapest_path, &sorted_path, &dNumGroups);

            /*
             * If grouping, decide whether to use sorted or hashed grouping.
             */
            if (parse->groupClause)
            {
                  bool        can_hash;
                  bool        can_sort;

                  /*
                   * Executor doesn't support hashed aggregation with DISTINCT
                   * aggregates.    (Doing so would imply storing *all* the input
                   * values in the hash table, which seems like a certain loser.)
                   */
                  can_hash = (agg_counts.numDistinctAggs == 0 &&
                                    grouping_is_hashable(parse->groupClause));
                  can_sort = grouping_is_sortable(parse->groupClause);
                  if (can_hash && can_sort)
                  {
                        /* we have a meaningful choice to make ... */
                        use_hashed_grouping =
                              choose_hashed_grouping(root,
                                                               tuple_fraction, limit_tuples,
                                                               cheapest_path, sorted_path,
                                                               dNumGroups, &agg_counts);
                  }
                  else if (can_hash)
                        use_hashed_grouping = true;
                  else if (can_sort)
                        use_hashed_grouping = false;
                  else
                        ereport(ERROR,
                                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                     errmsg("could not implement GROUP BY"),
                                     errdetail("Some of the datatypes only support hashing, while others only support sorting.")));

                  /* Also convert # groups to long int --- but 'ware overflow! */
                  numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
            }

            /*
             * Select the best path.  If we are doing hashed grouping, we will
             * always read all the input tuples, so use the cheapest-total path.
             * Otherwise, trust query_planner's decision about which to use.
             */
            if (use_hashed_grouping || !sorted_path)
                  best_path = cheapest_path;
            else
                  best_path = sorted_path;

            /*
             * Check to see if it's possible to optimize MIN/MAX aggregates. If
             * so, we will forget all the work we did so far to choose a "regular"
             * path ... but we had to do it anyway to be able to tell which way is
             * cheaper.
             */
            result_plan = optimize_minmax_aggregates(root,
                                                                         tlist,
                                                                         best_path);
            if (result_plan != NULL)
            {
                  /*
                   * optimize_minmax_aggregates generated the full plan, with the
                   * right tlist, and it has no sort order.
                   */
                  current_pathkeys = NIL;
            }
            else
            {
                  /*
                   * Normal case --- create a plan according to query_planner's
                   * results.
                   */
                  bool        need_sort_for_grouping = false;

                  result_plan = create_plan(root, best_path);
                  current_pathkeys = best_path->pathkeys;

                  /* Detect if we'll need an explicit sort for grouping */
                  if (parse->groupClause && !use_hashed_grouping &&
                    !pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
                  {
                        need_sort_for_grouping = true;

                        /*
                         * Always override query_planner's tlist, so that we don't
                         * sort useless data from a "physical" tlist.
                         */
                        need_tlist_eval = true;
                  }

                  /*
                   * create_plan() returns a plan with just a "flat" tlist of
                   * required Vars.  Usually we need to insert the sub_tlist as the
                   * tlist of the top plan node.      However, we can skip that if we
                   * determined that whatever query_planner chose to return will be
                   * good enough.
                   */
                  if (need_tlist_eval)
                  {
                        /*
                         * If the top-level plan node is one that cannot do expression
                         * evaluation, we must insert a Result node to project the
                         * desired tlist.
                         */
                        if (!is_projection_capable_plan(result_plan))
                        {
                              result_plan = (Plan *) make_result(root,
                                                                                 sub_tlist,
                                                                                 NULL,
                                                                                 result_plan);
                        }
                        else
                        {
                              /*
                               * Otherwise, just replace the subplan's flat tlist with
                               * the desired tlist.
                               */
                              result_plan->targetlist = sub_tlist;
                        }

                        /*
                         * Also, account for the cost of evaluation of the sub_tlist.
                         *
                         * Up to now, we have only been dealing with "flat" tlists,
                         * containing just Vars.  So their evaluation cost is zero
                         * according to the model used by cost_qual_eval() (or if you
                         * prefer, the cost is factored into cpu_tuple_cost).  Thus we
                         * can avoid accounting for tlist cost throughout
                         * query_planner() and subroutines.  But now we've inserted a
                         * tlist that might contain actual operators, sub-selects, etc
                         * --- so we'd better account for its cost.
                         *
                         * Below this point, any tlist eval cost for added-on nodes
                         * should be accounted for as we create those nodes.
                         * Presently, of the node types we can add on, only Agg,
                         * WindowAgg, and Group project new tlists (the rest just copy
                         * their input tuples) --- so make_agg(), make_windowagg() and
                         * make_group() are responsible for computing the added cost.
                         */
                        cost_qual_eval(&tlist_cost, sub_tlist, root);
                        result_plan->startup_cost += tlist_cost.startup;
                        result_plan->total_cost += tlist_cost.startup +
                              tlist_cost.per_tuple * result_plan->plan_rows;
                  }
                  else
                  {
                        /*
                         * Since we're using query_planner's tlist and not the one
                         * make_subplanTargetList calculated, we have to refigure any
                         * grouping-column indexes make_subplanTargetList computed.
                         */
                        locate_grouping_columns(root, tlist, result_plan->targetlist,
                                                            groupColIdx);
                  }

                  /*
                   * Insert AGG or GROUP node if needed, plus an explicit sort step
                   * if necessary.
                   *
                   * HAVING clause, if any, becomes qual of the Agg or Group node.
                   */
                  if (use_hashed_grouping)
                  {
                        /* Hashed aggregate plan --- no sort needed */
                        result_plan = (Plan *) make_agg(root,
                                                                        tlist,
                                                                        (List *) parse->havingQual,
                                                                        AGG_HASHED,
                                                                        numGroupCols,
                                                                        groupColIdx,
                                                      extract_grouping_ops(parse->groupClause),
                                                                        numGroups,
                                                                        agg_counts.numAggs,
                                                                        result_plan);
                        /* Hashed aggregation produces randomly-ordered results */
                        current_pathkeys = NIL;
                  }
                  else if (parse->hasAggs)
                  {
                        /* Plain aggregate plan --- sort if needed */
                        AggStrategy aggstrategy;

                        if (parse->groupClause)
                        {
                              if (need_sort_for_grouping)
                              {
                                    result_plan = (Plan *)
                                          make_sort_from_groupcols(root,
                                                                               parse->groupClause,
                                                                               groupColIdx,
                                                                               result_plan);
                                    current_pathkeys = root->group_pathkeys;
                              }
                              aggstrategy = AGG_SORTED;

                              /*
                               * The AGG node will not change the sort ordering of its
                               * groups, so current_pathkeys describes the result too.
                               */
                        }
                        else
                        {
                              aggstrategy = AGG_PLAIN;
                              /* Result will be only one row anyway; no sort order */
                              current_pathkeys = NIL;
                        }

                        result_plan = (Plan *) make_agg(root,
                                                                        tlist,
                                                                        (List *) parse->havingQual,
                                                                        aggstrategy,
                                                                        numGroupCols,
                                                                        groupColIdx,
                                                      extract_grouping_ops(parse->groupClause),
                                                                        numGroups,
                                                                        agg_counts.numAggs,
                                                                        result_plan);
                  }
                  else if (parse->groupClause)
                  {
                        /*
                         * GROUP BY without aggregation, so insert a group node (plus
                         * the appropriate sort node, if necessary).
                         *
                         * Add an explicit sort if we couldn't make the path come out
                         * the way the GROUP node needs it.
                         */
                        if (need_sort_for_grouping)
                        {
                              result_plan = (Plan *)
                                    make_sort_from_groupcols(root,
                                                                         parse->groupClause,
                                                                         groupColIdx,
                                                                         result_plan);
                              current_pathkeys = root->group_pathkeys;
                        }

                        result_plan = (Plan *) make_group(root,
                                                                          tlist,
                                                                          (List *) parse->havingQual,
                                                                          numGroupCols,
                                                                          groupColIdx,
                                                      extract_grouping_ops(parse->groupClause),
                                                                          dNumGroups,
                                                                          result_plan);
                        /* The Group node won't change sort ordering */
                  }
                  else if (root->hasHavingQual)
                  {
                        /*
                         * No aggregates, and no GROUP BY, but we have a HAVING qual.
                         * This is a degenerate case in which we are supposed to emit
                         * either 0 or 1 row depending on whether HAVING succeeds.
                         * Furthermore, there cannot be any variables in either HAVING
                         * or the targetlist, so we actually do not need the FROM
                         * table at all!  We can just throw away the plan-so-far and
                         * generate a Result node.    This is a sufficiently unusual
                         * corner case that it's not worth contorting the structure of
                         * this routine to avoid having to generate the plan in the
                         * first place.
                         */
                        result_plan = (Plan *) make_result(root,
                                                                           tlist,
                                                                           parse->havingQual,
                                                                           NULL);
                  }
            }                                   /* end of non-minmax-aggregate case */

            /*
             * Since each window function could require a different sort order, we
             * stack up a WindowAgg node for each window, with sort steps between
             * them as needed.
             */
            if (activeWindows)
            {
                  List     *window_tlist;
                  ListCell   *l;

                  /*
                   * If the top-level plan node is one that cannot do expression
                   * evaluation, we must insert a Result node to project the desired
                   * tlist.  (In some cases this might not really be required, but
                   * it's not worth trying to avoid it.)  Note that on second and
                   * subsequent passes through the following loop, the top-level
                   * node will be a WindowAgg which we know can project; so we only
                   * need to check once.
                   */
                  if (!is_projection_capable_plan(result_plan))
                  {
                        result_plan = (Plan *) make_result(root,
                                                                           NIL,
                                                                           NULL,
                                                                           result_plan);
                  }

                  /*
                   * The "base" targetlist for all steps of the windowing process is
                   * a flat tlist of all Vars and Aggs needed in the result. (In
                   * some cases we wouldn't need to propagate all of these all the
                   * way to the top, since they might only be needed as inputs to
                   * WindowFuncs.  It's probably not worth trying to optimize that
                   * though.)  We also need any volatile sort expressions, because
                   * make_sort_from_pathkeys won't add those on its own, and anyway
                   * we want them evaluated only once at the bottom of the stack.
                   * As we climb up the stack, we add outputs for the WindowFuncs
                   * computed at each level.    Also, each input tlist has to present
                   * all the columns needed to sort the data for the next WindowAgg
                   * step.  That's handled internally by make_sort_from_pathkeys,
                   * but we need the copyObject steps here to ensure that each plan
                   * node has a separately modifiable tlist.
                   */
                  window_tlist = flatten_tlist(tlist);
                  if (parse->hasAggs)
                        window_tlist = add_to_flat_tlist(window_tlist,
                                                                  pull_agg_clause((Node *) tlist));
                  window_tlist = add_volatile_sort_exprs(window_tlist, tlist,
                                                                           activeWindows);
                  result_plan->targetlist = (List *) copyObject(window_tlist);

                  foreach(l, activeWindows)
                  {
                        WindowClause *wc = (WindowClause *) lfirst(l);
                        List     *window_pathkeys;
                        int               partNumCols;
                        AttrNumber *partColIdx;
                        Oid            *partOperators;
                        int               ordNumCols;
                        AttrNumber *ordColIdx;
                        Oid            *ordOperators;

                        window_pathkeys = make_pathkeys_for_window(root,
                                                                                       wc,
                                                                                       tlist,
                                                                                       true);

                        /*
                         * This is a bit tricky: we build a sort node even if we don't
                         * really have to sort.  Even when no explicit sort is needed,
                         * we need to have suitable resjunk items added to the input
                         * plan's tlist for any partitioning or ordering columns that
                         * aren't plain Vars.  Furthermore, this way we can use
                         * existing infrastructure to identify which input columns are
                         * the interesting ones.
                         */
                        if (window_pathkeys)
                        {
                              Sort     *sort_plan;

                              sort_plan = make_sort_from_pathkeys(root,
                                                                                    result_plan,
                                                                                    window_pathkeys,
                                                                                    -1.0);
                              if (!pathkeys_contained_in(window_pathkeys,
                                                                     current_pathkeys))
                              {
                                    /* we do indeed need to sort */
                                    result_plan = (Plan *) sort_plan;
                                    current_pathkeys = window_pathkeys;
                              }
                              /* In either case, extract the per-column information */
                              get_column_info_for_window(root, wc, tlist,
                                                                     sort_plan->numCols,
                                                                     sort_plan->sortColIdx,
                                                                     &partNumCols,
                                                                     &partColIdx,
                                                                     &partOperators,
                                                                     &ordNumCols,
                                                                     &ordColIdx,
                                                                     &ordOperators);
                        }
                        else
                        {
                              /* empty window specification, nothing to sort */
                              partNumCols = 0;
                              partColIdx = NULL;
                              partOperators = NULL;
                              ordNumCols = 0;
                              ordColIdx = NULL;
                              ordOperators = NULL;
                        }

                        if (lnext(l))
                        {
                              /* Add the current WindowFuncs to the running tlist */
                              window_tlist = add_to_flat_tlist(window_tlist,
                                                               wflists->windowFuncs[wc->winref]);
                        }
                        else
                        {
                              /* Install the original tlist in the topmost WindowAgg */
                              window_tlist = tlist;
                        }

                        /* ... and make the WindowAgg plan node */
                        result_plan = (Plan *)
                              make_windowagg(root,
                                                   (List *) copyObject(window_tlist),
                                             list_length(wflists->windowFuncs[wc->winref]),
                                                   wc->winref,
                                                   partNumCols,
                                                   partColIdx,
                                                   partOperators,
                                                   ordNumCols,
                                                   ordColIdx,
                                                   ordOperators,
                                                   wc->frameOptions,
                                                   result_plan);
                  }
            }
      }                                         /* end of if (setOperations) */

      /*
       * If there is a DISTINCT clause, add the necessary node(s).
       */
      if (parse->distinctClause)
      {
            double            dNumDistinctRows;
            long        numDistinctRows;
            bool        use_hashed_distinct;
            bool        can_sort;
            bool        can_hash;

            /*
             * If there was grouping or aggregation, use the current number of
             * rows as the estimated number of DISTINCT rows (ie, assume the
             * result was already mostly unique).  If not, use the number of
             * distinct-groups calculated by query_planner.
             */
            if (parse->groupClause || root->hasHavingQual || parse->hasAggs)
                  dNumDistinctRows = result_plan->plan_rows;
            else
                  dNumDistinctRows = dNumGroups;

            /* Also convert to long int --- but 'ware overflow! */
            numDistinctRows = (long) Min(dNumDistinctRows, (double) LONG_MAX);

            /*
             * If we have a sortable DISTINCT ON clause, we always use sorting.
             * This enforces the expected behavior of DISTINCT ON.
             */
            can_sort = grouping_is_sortable(parse->distinctClause);
            if (can_sort && parse->hasDistinctOn)
                  use_hashed_distinct = false;
            else
            {
                  can_hash = grouping_is_hashable(parse->distinctClause);
                  if (can_hash && can_sort)
                  {
                        /* we have a meaningful choice to make ... */
                        use_hashed_distinct =
                              choose_hashed_distinct(root,
                                                               result_plan, current_pathkeys,
                                                               tuple_fraction, limit_tuples,
                                                               dNumDistinctRows);
                  }
                  else if (can_hash)
                        use_hashed_distinct = true;
                  else if (can_sort)
                        use_hashed_distinct = false;
                  else
                  {
                        ereport(ERROR,
                                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                     errmsg("could not implement DISTINCT"),
                                     errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
                        use_hashed_distinct = false;  /* keep compiler quiet */
                  }
            }

            if (use_hashed_distinct)
            {
                  /* Hashed aggregate plan --- no sort needed */
                  result_plan = (Plan *) make_agg(root,
                                                                  result_plan->targetlist,
                                                                  NIL,
                                                                  AGG_HASHED,
                                                              list_length(parse->distinctClause),
                                                 extract_grouping_cols(parse->distinctClause,
                                                                              result_plan->targetlist),
                                                 extract_grouping_ops(parse->distinctClause),
                                                                  numDistinctRows,
                                                                  0,
                                                                  result_plan);
                  /* Hashed aggregation produces randomly-ordered results */
                  current_pathkeys = NIL;
            }
            else
            {
                  /*
                   * Use a Unique node to implement DISTINCT.  Add an explicit sort
                   * if we couldn't make the path come out the way the Unique node
                   * needs it.  If we do have to sort, always sort by the more
                   * rigorous of DISTINCT and ORDER BY, to avoid a second sort
                   * below.  However, for regular DISTINCT, don't sort now if we
                   * don't have to --- sorting afterwards will likely be cheaper,
                   * and also has the possibility of optimizing via LIMIT.  But for
                   * DISTINCT ON, we *must* force the final sort now, else it won't
                   * have the desired behavior.
                   */
                  List     *needed_pathkeys;

                  if (parse->hasDistinctOn &&
                        list_length(root->distinct_pathkeys) <
                        list_length(root->sort_pathkeys))
                        needed_pathkeys = root->sort_pathkeys;
                  else
                        needed_pathkeys = root->distinct_pathkeys;

                  if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
                  {
                        if (list_length(root->distinct_pathkeys) >=
                              list_length(root->sort_pathkeys))
                              current_pathkeys = root->distinct_pathkeys;
                        else
                        {
                              current_pathkeys = root->sort_pathkeys;
                              /* Assert checks that parser didn't mess up... */
                              Assert(pathkeys_contained_in(root->distinct_pathkeys,
                                                                         current_pathkeys));
                        }

                        result_plan = (Plan *) make_sort_from_pathkeys(root,
                                                                                             result_plan,
                                                                                          current_pathkeys,
                                                                                             -1.0);
                  }

                  result_plan = (Plan *) make_unique(result_plan,
                                                                     parse->distinctClause);
                  result_plan->plan_rows = dNumDistinctRows;
                  /* The Unique node won't change sort ordering */
            }
      }

      /*
       * If ORDER BY was given and we were not able to make the plan come out in
       * the right order, add an explicit sort step.
       */
      if (parse->sortClause)
      {
            if (!pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
            {
                  result_plan = (Plan *) make_sort_from_pathkeys(root,
                                                                                       result_plan,
                                                                                     root->sort_pathkeys,
                                                                                       limit_tuples);
                  current_pathkeys = root->sort_pathkeys;
            }
      }

      /*
       * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
       */
      if (parse->limitCount || parse->limitOffset)
      {
            result_plan = (Plan *) make_limit(result_plan,
                                                              parse->limitOffset,
                                                              parse->limitCount,
                                                              offset_est,
                                                              count_est);
      }

      /*
       * Deal with the RETURNING clause if any.  It's convenient to pass the
       * returningList through setrefs.c now rather than at top level (if we
       * waited, handling inherited UPDATE/DELETE would be much harder).
       */
      if (parse->returningList)
      {
            List     *rlist;

            Assert(parse->resultRelation);
            rlist = set_returning_clause_references(root->glob,
                                                                        parse->returningList,
                                                                        result_plan,
                                                                        parse->resultRelation);
            root->returningLists = list_make1(rlist);
      }
      else
            root->returningLists = NIL;

      /* Compute result-relations list if needed */
      if (parse->resultRelation)
            root->resultRelations = list_make1_int(parse->resultRelation);
      else
            root->resultRelations = NIL;

      /*
       * Return the actual output ordering in query_pathkeys for possible use by
       * an outer query level.
       */
      root->query_pathkeys = current_pathkeys;

      return result_plan;
}

/*
 * Detect whether a plan node is a "dummy" plan created when a relation
 * is deemed not to need scanning due to constraint exclusion.
 *
 * Currently, such dummy plans are Result nodes with constant FALSE
 * filter quals.
 */
static bool
is_dummy_plan(Plan *plan)
{
      if (IsA(plan, Result))
      {
            List     *rcqual = (List *) ((Result *) plan)->resconstantqual;

            if (list_length(rcqual) == 1)
            {
                  Const    *constqual = (Const *) linitial(rcqual);

                  if (constqual && IsA(constqual, Const))
                  {
                        if (!constqual->constisnull &&
                              !DatumGetBool(constqual->constvalue))
                              return true;
                  }
            }
      }
      return false;
}

/*
 * preprocess_limit - do pre-estimation for LIMIT and/or OFFSET clauses
 *
 * We try to estimate the values of the LIMIT/OFFSET clauses, and pass the
 * results back in *count_est and *offset_est.  These variables are set to
 * 0 if the corresponding clause is not present, and -1 if it's present
 * but we couldn't estimate the value for it.  (The "0" convention is OK
 * for OFFSET but a little bit bogus for LIMIT: effectively we estimate
 * LIMIT 0 as though it were LIMIT 1.  But this is in line with the planner's
 * usual practice of never estimating less than one row.)  These values will
 * be passed to make_limit, which see if you change this code.
 *
 * The return value is the suitably adjusted tuple_fraction to use for
 * planning the query.  This adjustment is not overridable, since it reflects
 * plan actions that grouping_planner() will certainly take, not assumptions
 * about context.
 */
static double
preprocess_limit(PlannerInfo *root, double tuple_fraction,
                         int64 *offset_est, int64 *count_est)
{
      Query    *parse = root->parse;
      Node     *est;
      double            limit_fraction;

      /* Should not be called unless LIMIT or OFFSET */
      Assert(parse->limitCount || parse->limitOffset);

      /*
       * Try to obtain the clause values.  We use estimate_expression_value
       * primarily because it can sometimes do something useful with Params.
       */
      if (parse->limitCount)
      {
            est = estimate_expression_value(root, parse->limitCount);
            if (est && IsA(est, Const))
            {
                  if (((Const *) est)->constisnull)
                  {
                        /* NULL indicates LIMIT ALL, ie, no limit */
                        *count_est = 0; /* treat as not present */
                  }
                  else
                  {
                        *count_est = DatumGetInt64(((Const *) est)->constvalue);
                        if (*count_est <= 0)
                              *count_est = 1;         /* force to at least 1 */
                  }
            }
            else
                  *count_est = -1;  /* can't estimate */
      }
      else
            *count_est = 0;               /* not present */

      if (parse->limitOffset)
      {
            est = estimate_expression_value(root, parse->limitOffset);
            if (est && IsA(est, Const))
            {
                  if (((Const *) est)->constisnull)
                  {
                        /* Treat NULL as no offset; the executor will too */
                        *offset_est = 0;  /* treat as not present */
                  }
                  else
                  {
                        *offset_est = DatumGetInt64(((Const *) est)->constvalue);
                        if (*offset_est < 0)
                              *offset_est = 0;  /* less than 0 is same as 0 */
                  }
            }
            else
                  *offset_est = -1; /* can't estimate */
      }
      else
            *offset_est = 0;        /* not present */

      if (*count_est != 0)
      {
            /*
             * A LIMIT clause limits the absolute number of tuples returned.
             * However, if it's not a constant LIMIT then we have to guess; for
             * lack of a better idea, assume 10% of the plan's result is wanted.
             */
            if (*count_est < 0 || *offset_est < 0)
            {
                  /* LIMIT or OFFSET is an expression ... punt ... */
                  limit_fraction = 0.10;
            }
            else
            {
                  /* LIMIT (plus OFFSET, if any) is max number of tuples needed */
                  limit_fraction = (double) *count_est + (double) *offset_est;
            }

            /*
             * If we have absolute limits from both caller and LIMIT, use the
             * smaller value; likewise if they are both fractional.  If one is
             * fractional and the other absolute, we can't easily determine which
             * is smaller, but we use the heuristic that the absolute will usually
             * be smaller.
             */
            if (tuple_fraction >= 1.0)
            {
                  if (limit_fraction >= 1.0)
                  {
                        /* both absolute */
                        tuple_fraction = Min(tuple_fraction, limit_fraction);
                  }
                  else
                  {
                        /* caller absolute, limit fractional; use caller's value */
                  }
            }
            else if (tuple_fraction > 0.0)
            {
                  if (limit_fraction >= 1.0)
                  {
                        /* caller fractional, limit absolute; use limit */
                        tuple_fraction = limit_fraction;
                  }
                  else
                  {
                        /* both fractional */
                        tuple_fraction = Min(tuple_fraction, limit_fraction);
                  }
            }
            else
            {
                  /* no info from caller, just use limit */
                  tuple_fraction = limit_fraction;
            }
      }
      else if (*offset_est != 0 && tuple_fraction > 0.0)
      {
            /*
             * We have an OFFSET but no LIMIT.  This acts entirely differently
             * from the LIMIT case: here, we need to increase rather than decrease
             * the caller's tuple_fraction, because the OFFSET acts to cause more
             * tuples to be fetched instead of fewer.  This only matters if we got
             * a tuple_fraction > 0, however.
             *
             * As above, use 10% if OFFSET is present but unestimatable.
             */
            if (*offset_est < 0)
                  limit_fraction = 0.10;
            else
                  limit_fraction = (double) *offset_est;

            /*
             * If we have absolute counts from both caller and OFFSET, add them
             * together; likewise if they are both fractional.    If one is
             * fractional and the other absolute, we want to take the larger, and
             * we heuristically assume that's the fractional one.
             */
            if (tuple_fraction >= 1.0)
            {
                  if (limit_fraction >= 1.0)
                  {
                        /* both absolute, so add them together */
                        tuple_fraction += limit_fraction;
                  }
                  else
                  {
                        /* caller absolute, limit fractional; use limit */
                        tuple_fraction = limit_fraction;
                  }
            }
            else
            {
                  if (limit_fraction >= 1.0)
                  {
                        /* caller fractional, limit absolute; use caller's value */
                  }
                  else
                  {
                        /* both fractional, so add them together */
                        tuple_fraction += limit_fraction;
                        if (tuple_fraction >= 1.0)
                              tuple_fraction = 0.0;         /* assume fetch all */
                  }
            }
      }

      return tuple_fraction;
}


/*
 * preprocess_groupclause - do preparatory work on GROUP BY clause
 *
 * The idea here is to adjust the ordering of the GROUP BY elements
 * (which in itself is semantically insignificant) to match ORDER BY,
 * thereby allowing a single sort operation to both implement the ORDER BY
 * requirement and set up for a Unique step that implements GROUP BY.
 *
 * In principle it might be interesting to consider other orderings of the
 * GROUP BY elements, which could match the sort ordering of other
 * possible plans (eg an indexscan) and thereby reduce cost.  We don't
 * bother with that, though.  Hashed grouping will frequently win anyway.
 *
 * Note: we need no comparable processing of the distinctClause because
 * the parser already enforced that that matches ORDER BY.
 */
static void
preprocess_groupclause(PlannerInfo *root)
{
      Query    *parse = root->parse;
      List     *new_groupclause;
      bool        partial_match;
      ListCell   *sl;
      ListCell   *gl;

      /* If no ORDER BY, nothing useful to do here */
      if (parse->sortClause == NIL)
            return;

      /*
       * Scan the ORDER BY clause and construct a list of matching GROUP BY
       * items, but only as far as we can make a matching prefix.
       *
       * This code assumes that the sortClause contains no duplicate items.
       */
      new_groupclause = NIL;
      foreach(sl, parse->sortClause)
      {
            SortGroupClause *sc = (SortGroupClause *) lfirst(sl);

            foreach(gl, parse->groupClause)
            {
                  SortGroupClause *gc = (SortGroupClause *) lfirst(gl);

                  if (equal(gc, sc))
                  {
                        new_groupclause = lappend(new_groupclause, gc);
                        break;
                  }
            }
            if (gl == NULL)
                  break;                        /* no match, so stop scanning */
      }

      /* Did we match all of the ORDER BY list, or just some of it? */
      partial_match = (sl != NULL);

      /* If no match at all, no point in reordering GROUP BY */
      if (new_groupclause == NIL)
            return;

      /*
       * Add any remaining GROUP BY items to the new list, but only if we were
       * able to make a complete match.  In other words, we only rearrange the
       * GROUP BY list if the result is that one list is a prefix of the other
       * --- otherwise there's no possibility of a common sort.  Also, give up
       * if there are any non-sortable GROUP BY items, since then there's no
       * hope anyway.
       */
      foreach(gl, parse->groupClause)
      {
            SortGroupClause *gc = (SortGroupClause *) lfirst(gl);

            if (list_member_ptr(new_groupclause, gc))
                  continue;               /* it matched an ORDER BY item */
            if (partial_match)
                  return;                       /* give up, no common sort possible */
            if (!OidIsValid(gc->sortop))
                  return;                       /* give up, GROUP BY can't be sorted */
            new_groupclause = lappend(new_groupclause, gc);
      }

      /* Success --- install the rearranged GROUP BY list */
      Assert(list_length(parse->groupClause) == list_length(new_groupclause));
      parse->groupClause = new_groupclause;
}

/*
 * choose_hashed_grouping - should we use hashed grouping?
 *
 * Note: this is only applied when both alternatives are actually feasible.
 */
static bool
choose_hashed_grouping(PlannerInfo *root,
                                 double tuple_fraction, double limit_tuples,
                                 Path *cheapest_path, Path *sorted_path,
                                 double dNumGroups, AggClauseCounts *agg_counts)
{
      int               numGroupCols = list_length(root->parse->groupClause);
      double            cheapest_path_rows;
      int               cheapest_path_width;
      Size        hashentrysize;
      List     *target_pathkeys;
      List     *current_pathkeys;
      Path        hashed_p;
      Path        sorted_p;

      /* Prefer sorting when enable_hashagg is off */
      if (!enable_hashagg)
            return false;

      /*
       * Don't do it if it doesn't look like the hashtable will fit into
       * work_mem.
       *
       * Beware here of the possibility that cheapest_path->parent is NULL. This
       * could happen if user does something silly like SELECT 'foo' GROUP BY 1;
       */
      if (cheapest_path->parent)
      {
            cheapest_path_rows = cheapest_path->parent->rows;
            cheapest_path_width = cheapest_path->parent->width;
      }
      else
      {
            cheapest_path_rows = 1; /* assume non-set result */
            cheapest_path_width = 100;          /* arbitrary */
      }

      /* Estimate per-hash-entry space at tuple width... */
      hashentrysize = MAXALIGN(cheapest_path_width) + MAXALIGN(sizeof(MinimalTupleData));
      /* plus space for pass-by-ref transition values... */
      hashentrysize += agg_counts->transitionSpace;
      /* plus the per-hash-entry overhead */
      hashentrysize += hash_agg_entry_size(agg_counts->numAggs);

      if (hashentrysize * dNumGroups > work_mem * 1024L)
            return false;

      /*
       * When we have both GROUP BY and DISTINCT, use the more-rigorous of
       * DISTINCT and ORDER BY as the assumed required output sort order. This
       * is an oversimplification because the DISTINCT might get implemented via
       * hashing, but it's not clear that the case is common enough (or that our
       * estimates are good enough) to justify trying to solve it exactly.
       */
      if (list_length(root->distinct_pathkeys) >
            list_length(root->sort_pathkeys))
            target_pathkeys = root->distinct_pathkeys;
      else
            target_pathkeys = root->sort_pathkeys;

      /*
       * See if the estimated cost is no more than doing it the other way. While
       * avoiding the need for sorted input is usually a win, the fact that the
       * output won't be sorted may be a loss; so we need to do an actual cost
       * comparison.
       *
       * We need to consider cheapest_path + hashagg [+ final sort] versus
       * either cheapest_path [+ sort] + group or agg [+ final sort] or
       * presorted_path + group or agg [+ final sort] where brackets indicate a
       * step that may not be needed. We assume query_planner() will have
       * returned a presorted path only if it's a winner compared to
       * cheapest_path for this purpose.
       *
       * These path variables are dummies that just hold cost fields; we don't
       * make actual Paths for these steps.
       */
      cost_agg(&hashed_p, root, AGG_HASHED, agg_counts->numAggs,
                   numGroupCols, dNumGroups,
                   cheapest_path->startup_cost, cheapest_path->total_cost,
                   cheapest_path_rows);
      /* Result of hashed agg is always unsorted */
      if (target_pathkeys)
            cost_sort(&hashed_p, root, target_pathkeys, hashed_p.total_cost,
                          dNumGroups, cheapest_path_width, limit_tuples);

      if (sorted_path)
      {
            sorted_p.startup_cost = sorted_path->startup_cost;
            sorted_p.total_cost = sorted_path->total_cost;
            current_pathkeys = sorted_path->pathkeys;
      }
      else
      {
            sorted_p.startup_cost = cheapest_path->startup_cost;
            sorted_p.total_cost = cheapest_path->total_cost;
            current_pathkeys = cheapest_path->pathkeys;
      }
      if (!pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
      {
            cost_sort(&sorted_p, root, root->group_pathkeys, sorted_p.total_cost,
                          cheapest_path_rows, cheapest_path_width, -1.0);
            current_pathkeys = root->group_pathkeys;
      }

      if (root->parse->hasAggs)
            cost_agg(&sorted_p, root, AGG_SORTED, agg_counts->numAggs,
                         numGroupCols, dNumGroups,
                         sorted_p.startup_cost, sorted_p.total_cost,
                         cheapest_path_rows);
      else
            cost_group(&sorted_p, root, numGroupCols, dNumGroups,
                           sorted_p.startup_cost, sorted_p.total_cost,
                           cheapest_path_rows);
      /* The Agg or Group node will preserve ordering */
      if (target_pathkeys &&
            !pathkeys_contained_in(target_pathkeys, current_pathkeys))
            cost_sort(&sorted_p, root, target_pathkeys, sorted_p.total_cost,
                          dNumGroups, cheapest_path_width, limit_tuples);

      /*
       * Now make the decision using the top-level tuple fraction.  First we
       * have to convert an absolute count (LIMIT) into fractional form.
       */
      if (tuple_fraction >= 1.0)
            tuple_fraction /= dNumGroups;

      if (compare_fractional_path_costs(&hashed_p, &sorted_p,
                                                        tuple_fraction) < 0)
      {
            /* Hashed is cheaper, so use it */
            return true;
      }
      return false;
}

/*
 * choose_hashed_distinct - should we use hashing for DISTINCT?
 *
 * This is fairly similar to choose_hashed_grouping, but there are enough
 * differences that it doesn't seem worth trying to unify the two functions.
 *
 * But note that making the two choices independently is a bit bogus in
 * itself.  If the two could be combined into a single choice operation
 * it'd probably be better, but that seems far too unwieldy to be practical,
 * especially considering that the combination of GROUP BY and DISTINCT
 * isn't very common in real queries.  By separating them, we are giving
 * extra preference to using a sorting implementation when a common sort key
 * is available ... and that's not necessarily wrong anyway.
 *
 * Note: this is only applied when both alternatives are actually feasible.
 */
static bool
choose_hashed_distinct(PlannerInfo *root,
                                 Plan *input_plan, List *input_pathkeys,
                                 double tuple_fraction, double limit_tuples,
                                 double dNumDistinctRows)
{
      int               numDistinctCols = list_length(root->parse->distinctClause);
      Size        hashentrysize;
      List     *current_pathkeys;
      List     *needed_pathkeys;
      Path        hashed_p;
      Path        sorted_p;

      /* Prefer sorting when enable_hashagg is off */
      if (!enable_hashagg)
            return false;

      /*
       * Don't do it if it doesn't look like the hashtable will fit into
       * work_mem.
       */
      hashentrysize = MAXALIGN(input_plan->plan_width) + MAXALIGN(sizeof(MinimalTupleData));

      if (hashentrysize * dNumDistinctRows > work_mem * 1024L)
            return false;

      /*
       * See if the estimated cost is no more than doing it the other way. While
       * avoiding the need for sorted input is usually a win, the fact that the
       * output won't be sorted may be a loss; so we need to do an actual cost
       * comparison.
       *
       * We need to consider input_plan + hashagg [+ final sort] versus
       * input_plan [+ sort] + group [+ final sort] where brackets indicate a
       * step that may not be needed.
       *
       * These path variables are dummies that just hold cost fields; we don't
       * make actual Paths for these steps.
       */
      cost_agg(&hashed_p, root, AGG_HASHED, 0,
                   numDistinctCols, dNumDistinctRows,
                   input_plan->startup_cost, input_plan->total_cost,
                   input_plan->plan_rows);

      /*
       * Result of hashed agg is always unsorted, so if ORDER BY is present we
       * need to charge for the final sort.
       */
      if (root->parse->sortClause)
            cost_sort(&hashed_p, root, root->sort_pathkeys, hashed_p.total_cost,
                          dNumDistinctRows, input_plan->plan_width, limit_tuples);

      /*
       * Now for the GROUP case.    See comments in grouping_planner about the
       * sorting choices here --- this code should match that code.
       */
      sorted_p.startup_cost = input_plan->startup_cost;
      sorted_p.total_cost = input_plan->total_cost;
      current_pathkeys = input_pathkeys;
      if (root->parse->hasDistinctOn &&
            list_length(root->distinct_pathkeys) <
            list_length(root->sort_pathkeys))
            needed_pathkeys = root->sort_pathkeys;
      else
            needed_pathkeys = root->distinct_pathkeys;
      if (!pathkeys_contained_in(needed_pathkeys, current_pathkeys))
      {
            if (list_length(root->distinct_pathkeys) >=
                  list_length(root->sort_pathkeys))
                  current_pathkeys = root->distinct_pathkeys;
            else
                  current_pathkeys = root->sort_pathkeys;
            cost_sort(&sorted_p, root, current_pathkeys, sorted_p.total_cost,
                          input_plan->plan_rows, input_plan->plan_width, -1.0);
      }
      cost_group(&sorted_p, root, numDistinctCols, dNumDistinctRows,
                     sorted_p.startup_cost, sorted_p.total_cost,
                     input_plan->plan_rows);
      if (root->parse->sortClause &&
            !pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
            cost_sort(&sorted_p, root, root->sort_pathkeys, sorted_p.total_cost,
                          dNumDistinctRows, input_plan->plan_width, limit_tuples);

      /*
       * Now make the decision using the top-level tuple fraction.  First we
       * have to convert an absolute count (LIMIT) into fractional form.
       */
      if (tuple_fraction >= 1.0)
            tuple_fraction /= dNumDistinctRows;

      if (compare_fractional_path_costs(&hashed_p, &sorted_p,
                                                        tuple_fraction) < 0)
      {
            /* Hashed is cheaper, so use it */
            return true;
      }
      return false;
}

/*---------------
 * make_subplanTargetList
 *      Generate appropriate target list when grouping is required.
 *
 * When grouping_planner inserts Aggregate, Group, or Result plan nodes
 * above the result of query_planner, we typically want to pass a different
 * target list to query_planner than the outer plan nodes should have.
 * This routine generates the correct target list for the subplan.
 *
 * The initial target list passed from the parser already contains entries
 * for all ORDER BY and GROUP BY expressions, but it will not have entries
 * for variables used only in HAVING clauses; so we need to add those
 * variables to the subplan target list.  Also, we flatten all expressions
 * except GROUP BY items into their component variables; the other expressions
 * will be computed by the inserted nodes rather than by the subplan.
 * For example, given a query like
 *          SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
 * we want to pass this targetlist to the subplan:
 *          a,b,c,d,a+b
 * where the a+b target will be used by the Sort/Group steps, and the
 * other targets will be used for computing the final results.    (In the
 * above example we could theoretically suppress the a and b targets and
 * pass down only c,d,a+b, but it's not really worth the trouble to
 * eliminate simple var references from the subplan.  We will avoid doing
 * the extra computation to recompute a+b at the outer level; see
 * fix_upper_expr() in setrefs.c.)
 *
 * If we are grouping or aggregating, *and* there are no non-Var grouping
 * expressions, then the returned tlist is effectively dummy; we do not
 * need to force it to be evaluated, because all the Vars it contains
 * should be present in the output of query_planner anyway.
 *
 * 'tlist' is the query's target list.
 * 'groupColIdx' receives an array of column numbers for the GROUP BY
 *                expressions (if there are any) in the subplan's target list.
 * 'need_tlist_eval' is set true if we really need to evaluate the
 *                result tlist.
 *
 * The result is the targetlist to be passed to the subplan.
 *---------------
 */
static List *
make_subplanTargetList(PlannerInfo *root,
                                 List *tlist,
                                 AttrNumber **groupColIdx,
                                 bool *need_tlist_eval)
{
      Query    *parse = root->parse;
      List     *sub_tlist;
      List     *extravars;
      int               numCols;

      *groupColIdx = NULL;

      /*
       * If we're not grouping or aggregating, there's nothing to do here;
       * query_planner should receive the unmodified target list.
       */
      if (!parse->hasAggs && !parse->groupClause && !root->hasHavingQual &&
            !parse->hasWindowFuncs)
      {
            *need_tlist_eval = true;
            return tlist;
      }

      /*
       * Otherwise, start with a "flattened" tlist (having just the vars
       * mentioned in the targetlist and HAVING qual --- but not upper-level
       * Vars; they will be replaced by Params later on).  Note this includes
       * vars used in resjunk items, so we are covering the needs of ORDER BY
       * and window specifications.
       */
      sub_tlist = flatten_tlist(tlist);
      extravars = pull_var_clause(parse->havingQual, PVC_INCLUDE_PLACEHOLDERS);
      sub_tlist = add_to_flat_tlist(sub_tlist, extravars);
      list_free(extravars);
      *need_tlist_eval = false;     /* only eval if not flat tlist */

      /*
       * If grouping, create sub_tlist entries for all GROUP BY expressions
       * (GROUP BY items that are simple Vars should be in the list already),
       * and make an array showing where the group columns are in the sub_tlist.
       */
      numCols = list_length(parse->groupClause);
      if (numCols > 0)
      {
            int               keyno = 0;
            AttrNumber *grpColIdx;
            ListCell   *gl;

            grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
            *groupColIdx = grpColIdx;

            foreach(gl, parse->groupClause)
            {
                  SortGroupClause *grpcl = (SortGroupClause *) lfirst(gl);
                  Node     *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
                  TargetEntry *te;

                  /*
                   * Find or make a matching sub_tlist entry.  If the groupexpr
                   * isn't a Var, no point in searching.  (Note that the parser
                   * won't make multiple groupClause entries for the same TLE.)
                   */
                  if (groupexpr && IsA(groupexpr, Var))
                        te = tlist_member(groupexpr, sub_tlist);
                  else
                        te = NULL;

                  if (!te)
                  {
                        te = makeTargetEntry((Expr *) groupexpr,
                                                       list_length(sub_tlist) + 1,
                                                       NULL,
                                                       false);
                        sub_tlist = lappend(sub_tlist, te);
                        *need_tlist_eval = true;            /* it's not flat anymore */
                  }

                  /* and save its resno */
                  grpColIdx[keyno++] = te->resno;
            }
      }

      return sub_tlist;
}

/*
 * locate_grouping_columns
 *          Locate grouping columns in the tlist chosen by query_planner.
 *
 * This is only needed if we don't use the sub_tlist chosen by
 * make_subplanTargetList.    We have to forget the column indexes found
 * by that routine and re-locate the grouping exprs in the real sub_tlist.
 */
static void
locate_grouping_columns(PlannerInfo *root,
                                    List *tlist,
                                    List *sub_tlist,
                                    AttrNumber *groupColIdx)
{
      int               keyno = 0;
      ListCell   *gl;

      /*
       * No work unless grouping.
       */
      if (!root->parse->groupClause)
      {
            Assert(groupColIdx == NULL);
            return;
      }
      Assert(groupColIdx != NULL);

      foreach(gl, root->parse->groupClause)
      {
            SortGroupClause *grpcl = (SortGroupClause *) lfirst(gl);
            Node     *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
            TargetEntry *te = tlist_member(groupexpr, sub_tlist);

            if (!te)
                  elog(ERROR, "failed to locate grouping columns");
            groupColIdx[keyno++] = te->resno;
      }
}

/*
 * postprocess_setop_tlist
 *      Fix up targetlist returned by plan_set_operations().
 *
 * We need to transpose sort key info from the orig_tlist into new_tlist.
 * NOTE: this would not be good enough if we supported resjunk sort keys
 * for results of set operations --- then, we'd need to project a whole
 * new tlist to evaluate the resjunk columns.  For now, just ereport if we
 * find any resjunk columns in orig_tlist.
 */
static List *
postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
{
      ListCell   *l;
      ListCell   *orig_tlist_item = list_head(orig_tlist);

      foreach(l, new_tlist)
      {
            TargetEntry *new_tle = (TargetEntry *) lfirst(l);
            TargetEntry *orig_tle;

            /* ignore resjunk columns in setop result */
            if (new_tle->resjunk)
                  continue;

            Assert(orig_tlist_item != NULL);
            orig_tle = (TargetEntry *) lfirst(orig_tlist_item);
            orig_tlist_item = lnext(orig_tlist_item);
            if (orig_tle->resjunk)  /* should not happen */
                  elog(ERROR, "resjunk output columns are not implemented");
            Assert(new_tle->resno == orig_tle->resno);
            new_tle->ressortgroupref = orig_tle->ressortgroupref;
      }
      if (orig_tlist_item != NULL)
            elog(ERROR, "resjunk output columns are not implemented");
      return new_tlist;
}

/*
 * select_active_windows
 *          Create a list of the "active" window clauses (ie, those referenced
 *          by non-deleted WindowFuncs) in the order they are to be executed.
 */
static List *
select_active_windows(PlannerInfo *root, WindowFuncLists *wflists)
{
      List     *result;
      List     *actives;
      ListCell   *lc;

      /* First, make a list of the active windows */
      actives = NIL;
      foreach(lc, root->parse->windowClause)
      {
            WindowClause *wc = (WindowClause *) lfirst(lc);

            /* It's only active if wflists shows some related WindowFuncs */
            Assert(wc->winref <= wflists->maxWinRef);
            if (wflists->windowFuncs[wc->winref] != NIL)
                  actives = lappend(actives, wc);
      }

      /*
       * Now, ensure that windows with identical partitioning/ordering clauses
       * are adjacent in the list.  This is required by the SQL standard, which
       * says that only one sort is to be used for such windows, even if they
       * are otherwise distinct (eg, different names or framing clauses).
       *
       * There is room to be much smarter here, for example detecting whether
       * one window's sort keys are a prefix of another's (so that sorting for
       * the latter would do for the former), or putting windows first that
       * match a sort order available for the underlying query.  For the moment
       * we are content with meeting the spec.
       */
      result = NIL;
      while (actives != NIL)
      {
            WindowClause *wc = (WindowClause *) linitial(actives);
            ListCell   *prev;
            ListCell   *next;

            /* Move wc from actives to result */
            actives = list_delete_first(actives);
            result = lappend(result, wc);

            /* Now move any matching windows from actives to result */
            prev = NULL;
            for (lc = list_head(actives); lc; lc = next)
            {
                  WindowClause *wc2 = (WindowClause *) lfirst(lc);

                  next = lnext(lc);
                  /* framing options are NOT to be compared here! */
                  if (equal(wc->partitionClause, wc2->partitionClause) &&
                        equal(wc->orderClause, wc2->orderClause))
                  {
                        actives = list_delete_cell(actives, lc, prev);
                        result = lappend(result, wc2);
                  }
                  else
                        prev = lc;
            }
      }

      return result;
}

/*
 * add_volatile_sort_exprs
 *          Identify any volatile sort/group expressions used by the active
 *          windows, and add them to window_tlist if not already present.
 *          Return the modified window_tlist.
 */
static List *
add_volatile_sort_exprs(List *window_tlist, List *tlist, List *activeWindows)
{
      Bitmapset  *sgrefs = NULL;
      ListCell   *lc;

      /* First, collect the sortgrouprefs of the windows into a bitmapset */
      foreach(lc, activeWindows)
      {
            WindowClause *wc = (WindowClause *) lfirst(lc);
            ListCell   *lc2;

            foreach(lc2, wc->partitionClause)
            {
                  SortGroupClause *sortcl = (SortGroupClause *) lfirst(lc2);

                  sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
            }
            foreach(lc2, wc->orderClause)
            {
                  SortGroupClause *sortcl = (SortGroupClause *) lfirst(lc2);

                  sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
            }
      }

      /*
       * Now scan the original tlist to find the referenced expressions. Any
       * that are volatile must be added to window_tlist.
       *
       * Note: we know that the input window_tlist contains no items marked with
       * ressortgrouprefs, so we don't have to worry about collisions of the
       * reference numbers.
       */
      foreach(lc, tlist)
      {
            TargetEntry *tle = (TargetEntry *) lfirst(lc);

            if (tle->ressortgroupref != 0 &&
                  bms_is_member(tle->ressortgroupref, sgrefs) &&
                  contain_volatile_functions((Node *) tle->expr))
            {
                  TargetEntry *newtle;

                  newtle = makeTargetEntry(tle->expr,
                                                       list_length(window_tlist) + 1,
                                                       NULL,
                                                       false);
                  newtle->ressortgroupref = tle->ressortgroupref;
                  window_tlist = lappend(window_tlist, newtle);
            }
      }

      return window_tlist;
}

/*
 * make_pathkeys_for_window
 *          Create a pathkeys list describing the required input ordering
 *          for the given WindowClause.
 *
 * The required ordering is first the PARTITION keys, then the ORDER keys.
 * In the future we might try to implement windowing using hashing, in which
 * case the ordering could be relaxed, but for now we always sort.
 */
static List *
make_pathkeys_for_window(PlannerInfo *root, WindowClause *wc,
                                     List *tlist, bool canonicalize)
{
      List     *window_pathkeys;
      List     *window_sortclauses;

      /* Throw error if can't sort */
      if (!grouping_is_sortable(wc->partitionClause))
            ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("could not implement window PARTITION BY"),
                         errdetail("Window partitioning columns must be of sortable datatypes.")));
      if (!grouping_is_sortable(wc->orderClause))
            ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("could not implement window ORDER BY"),
            errdetail("Window ordering columns must be of sortable datatypes.")));

      /* Okay, make the combined pathkeys */
      window_sortclauses = list_concat(list_copy(wc->partitionClause),
                                                       list_copy(wc->orderClause));
      window_pathkeys = make_pathkeys_for_sortclauses(root,
                                                                              window_sortclauses,
                                                                              tlist,
                                                                              canonicalize);
      list_free(window_sortclauses);
      return window_pathkeys;
}

/*----------
 * get_column_info_for_window
 *          Get the partitioning/ordering column numbers and equality operators
 *          for a WindowAgg node.
 *
 * This depends on the behavior of make_pathkeys_for_window()!
 *
 * We are given the target WindowClause and an array of the input column
 * numbers associated with the resulting pathkeys.    In the easy case, there
 * are the same number of pathkey columns as partitioning + ordering columns
 * and we just have to copy some data around.  However, it's possible that
 * some of the original partitioning + ordering columns were eliminated as
 * redundant during the transformation to pathkeys.  (This can happen even
 * though the parser gets rid of obvious duplicates.  A typical scenario is a
 * window specification "PARTITION BY x ORDER BY y" coupled with a clause
 * "WHERE x = y" that causes the two sort columns to be recognized as
 * redundant.)    In that unusual case, we have to work a lot harder to
 * determine which keys are significant.
 *
 * The method used here is a bit brute-force: add the sort columns to a list
 * one at a time and note when the resulting pathkey list gets longer.  But
 * it's a sufficiently uncommon case that a faster way doesn't seem worth
 * the amount of code refactoring that'd be needed.
 *----------
 */
static void
get_column_info_for_window(PlannerInfo *root, WindowClause *wc, List *tlist,
                                       int numSortCols, AttrNumber *sortColIdx,
                                       int *partNumCols,
                                       AttrNumber **partColIdx,
                                       Oid **partOperators,
                                       int *ordNumCols,
                                       AttrNumber **ordColIdx,
                                       Oid **ordOperators)
{
      int               numPart = list_length(wc->partitionClause);
      int               numOrder = list_length(wc->orderClause);

      if (numSortCols == numPart + numOrder)
      {
            /* easy case */
            *partNumCols = numPart;
            *partColIdx = sortColIdx;
            *partOperators = extract_grouping_ops(wc->partitionClause);
            *ordNumCols = numOrder;
            *ordColIdx = sortColIdx + numPart;
            *ordOperators = extract_grouping_ops(wc->orderClause);
      }
      else
      {
            List     *sortclauses;
            List     *pathkeys;
            int               scidx;
            ListCell   *lc;

            /* first, allocate what's certainly enough space for the arrays */
            *partNumCols = 0;
            *partColIdx = (AttrNumber *) palloc(numPart * sizeof(AttrNumber));
            *partOperators = (Oid *) palloc(numPart * sizeof(Oid));
            *ordNumCols = 0;
            *ordColIdx = (AttrNumber *) palloc(numOrder * sizeof(AttrNumber));
            *ordOperators = (Oid *) palloc(numOrder * sizeof(Oid));
            sortclauses = NIL;
            pathkeys = NIL;
            scidx = 0;
            foreach(lc, wc->partitionClause)
            {
                  SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
                  List     *new_pathkeys;

                  sortclauses = lappend(sortclauses, sgc);
                  new_pathkeys = make_pathkeys_for_sortclauses(root,
                                                                                     sortclauses,
                                                                                     tlist,
                                                                                     true);
                  if (list_length(new_pathkeys) > list_length(pathkeys))
                  {
                        /* this sort clause is actually significant */
                        (*partColIdx)[*partNumCols] = sortColIdx[scidx++];
                        (*partOperators)[*partNumCols] = sgc->eqop;
                        (*partNumCols)++;
                        pathkeys = new_pathkeys;
                  }
            }
            foreach(lc, wc->orderClause)
            {
                  SortGroupClause *sgc = (SortGroupClause *) lfirst(lc);
                  List     *new_pathkeys;

                  sortclauses = lappend(sortclauses, sgc);
                  new_pathkeys = make_pathkeys_for_sortclauses(root,
                                                                                     sortclauses,
                                                                                     tlist,
                                                                                     true);
                  if (list_length(new_pathkeys) > list_length(pathkeys))
                  {
                        /* this sort clause is actually significant */
                        (*ordColIdx)[*ordNumCols] = sortColIdx[scidx++];
                        (*ordOperators)[*ordNumCols] = sgc->eqop;
                        (*ordNumCols)++;
                        pathkeys = new_pathkeys;
                  }
            }
            /* complain if we didn't eat exactly the right number of sort cols */
            if (scidx != numSortCols)
                  elog(ERROR, "failed to deconstruct sort operators into partitioning/ordering operators");
      }
}


/*
 * expression_planner
 *          Perform planner's transformations on a standalone expression.
 *
 * Various utility commands need to evaluate expressions that are not part
 * of a plannable query.  They can do so using the executor's regular
 * expression-execution machinery, but first the expression has to be fed
 * through here to transform it from parser output to something executable.
 *
 * Currently, we disallow sublinks in standalone expressions, so there's no
 * real "planning" involved here.  (That might not always be true though.)
 * What we must do is run eval_const_expressions to ensure that any function
 * default arguments get inserted.  The fact that constant subexpressions
 * get simplified is a side-effect that is useful when the expression will
 * get evaluated more than once.  Also, we must fix operator function IDs.
 *
 * Note: this must not make any damaging changes to the passed-in expression
 * tree.  (It would actually be okay to apply fix_opfuncids to it, but since
 * we first do an expression_tree_mutator-based walk, what is returned will
 * be a new node tree.)
 */
Expr *
expression_planner(Expr *expr)
{
      Node     *result;

      /* Insert default arguments and simplify constant subexprs */
      result = eval_const_expressions(NULL, (Node *) expr);

      /* Fill in opfuncid values if missing */
      fix_opfuncids(result);

      return (Expr *) result;
}

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