/*-------------------------------------------------------------------------
 *
 * planner.c
 *	  The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.185 2005/04/28 21:47:13 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>

#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#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"
#include "parser/parsetree.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"


ParamListInfo PlannerBoundParamList = NULL;		/* current boundParams */


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


static Node *preprocess_expression(Query *parse, Node *expr, int kind);
static void preprocess_qual_conditions(Query *parse, Node *jtnode);
static Plan *inheritance_planner(Query *parse, List *inheritlist);
static Plan *grouping_planner(Query *parse, double tuple_fraction);
static bool choose_hashed_grouping(Query *parse, double tuple_fraction,
					   Path *cheapest_path, Path *sorted_path,
					   List *sort_pathkeys, List *group_pathkeys,
					   double dNumGroups, AggClauseCounts *agg_counts);
static bool hash_safe_grouping(Query *parse);
static List *make_subplanTargetList(Query *parse, List *tlist,
					   AttrNumber **groupColIdx, bool *need_tlist_eval);
static void locate_grouping_columns(Query *parse,
						List *tlist,
						List *sub_tlist,
						AttrNumber *groupColIdx);
static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);


/*****************************************************************************
 *
 *	   Query optimizer entry point
 *
 *****************************************************************************/
Plan *
planner(Query *parse, bool isCursor, int cursorOptions,
		ParamListInfo boundParams)
{
	double		tuple_fraction;
	Plan	   *result_plan;
	Index		save_PlannerQueryLevel;
	List	   *save_PlannerParamList;
	ParamListInfo save_PlannerBoundParamList;

	/*
	 * The planner can be called recursively (an example is when
	 * eval_const_expressions tries to pre-evaluate an SQL function). So,
	 * these global state variables must be saved and restored.
	 *
	 * Query level and the param list cannot be moved into the Query
	 * structure since their whole purpose is communication across
	 * multiple sub-Queries. Also, boundParams is explicitly info from
	 * outside the Query, and so is likewise better handled as a global
	 * variable.
	 *
	 * Note we do NOT save and restore PlannerPlanId: it exists to assign
	 * unique IDs to SubPlan nodes, and we want those IDs to be unique for
	 * the life of a backend.  Also, PlannerInitPlan is saved/restored in
	 * subquery_planner, not here.
	 */
	save_PlannerQueryLevel = PlannerQueryLevel;
	save_PlannerParamList = PlannerParamList;
	save_PlannerBoundParamList = PlannerBoundParamList;

	/* Initialize state for handling outer-level references and params */
	PlannerQueryLevel = 0;		/* will be 1 in top-level subquery_planner */
	PlannerParamList = NIL;
	PlannerBoundParamList = boundParams;

	/* Determine what fraction of the plan is likely to be scanned */
	if (isCursor)
	{
		/*
		 * We have no real idea how many tuples the user will ultimately
		 * FETCH from a cursor, but it seems a good bet that he doesn't
		 * want 'em all.  Optimize for 10% retrieval (you gotta better
		 * number?	Should this be a SETtable parameter?)
		 */
		tuple_fraction = 0.10;
	}
	else
	{
		/* Default assumption is we need all the tuples */
		tuple_fraction = 0.0;
	}

	/* primary planning entry point (may recurse for subqueries) */
	result_plan = subquery_planner(parse, tuple_fraction);

	Assert(PlannerQueryLevel == 0);

	/*
	 * 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 (isCursor && (cursorOptions & CURSOR_OPT_SCROLL))
	{
		if (!ExecSupportsBackwardScan(result_plan))
			result_plan = materialize_finished_plan(result_plan);
	}

	/* executor wants to know total number of Params used overall */
	result_plan->nParamExec = list_length(PlannerParamList);

	/* final cleanup of the plan */
	set_plan_references(result_plan, parse->rtable);

	/* restore state for outer planner, if any */
	PlannerQueryLevel = save_PlannerQueryLevel;
	PlannerParamList = save_PlannerParamList;
	PlannerBoundParamList = save_PlannerBoundParamList;

	return result_plan;
}


/*--------------------
 * subquery_planner
 *	  Invokes the planner on a subquery.  We recurse to here for each
 *	  sub-SELECT found in the query tree.
 *
 * parse is the querytree produced by the parser & rewriter.
 * tuple_fraction is the fraction of tuples we expect will be retrieved.
 * tuple_fraction is interpreted as explained for grouping_planner, below.
 *
 * 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(Query *parse, double tuple_fraction)
{
	List	   *saved_initplan = PlannerInitPlan;
	int			saved_planid = PlannerPlanId;
	bool		hasOuterJoins;
	Plan	   *plan;
	List	   *newHaving;
	List	   *lst;
	ListCell   *l;

	/* Set up for a new level of subquery */
	PlannerQueryLevel++;
	PlannerInitPlan = NIL;

	/*
	 * Look for IN clauses at the top level of WHERE, and transform them
	 * into joins.	Note that this step only handles IN clauses originally
	 * at top level of WHERE; if we pull up any subqueries in the next
	 * step, their INs are processed just before pulling them up.
	 */
	parse->in_info_list = NIL;
	if (parse->hasSubLinks)
		parse->jointree->quals = pull_up_IN_clauses(parse,
												 parse->jointree->quals);

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

	/*
	 * 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.
	 */
	parse->hasJoinRTEs = false;
	hasOuterJoins = false;
	foreach(l, parse->rtable)
	{
		RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

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

	/*
	 * 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.
	 */
	parse->hasHavingQual = (parse->havingQual != NULL);

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

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

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

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

	parse->in_info_list = (List *)
		preprocess_expression(parse, (Node *) parse->in_info_list,
							  EXPRKIND_ININFO);

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

		if (rte->rtekind == RTE_FUNCTION)
			rte->funcexpr = preprocess_expression(parse, rte->funcexpr,
												  EXPRKIND_RTFUNC);
	}

	/*
	 * 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(parse);

	/*
	 * See if we can simplify the jointree; opportunities for this may
	 * come from having pulled up subqueries, or from flattening explicit
	 * JOIN syntax.  We must do this after flattening JOIN alias
	 * variables, since eliminating explicit JOIN nodes from the jointree
	 * will cause get_relids_for_join() to fail.  But it should happen
	 * after reduce_outer_joins, anyway.
	 */
	parse->jointree = (FromExpr *)
		simplify_jointree(parse, (Node *) parse->jointree);

	/*
	 * Do the main planning.  If we have an inherited target relation,
	 * that needs special processing, else go straight to
	 * grouping_planner.
	 */
	if (parse->resultRelation &&
		(lst = expand_inherited_rtentry(parse, parse->resultRelation)) != NIL)
		plan = inheritance_planner(parse, lst);
	else
		plan = grouping_planner(parse, 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 (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
		SS_finalize_plan(plan, parse->rtable);

	/* Return to outer subquery context */
	PlannerQueryLevel--;
	PlannerInitPlan = saved_initplan;
	/* we do NOT restore PlannerPlanId; that's not an oversight! */

	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(Query *parse, Node *expr, int kind)
{
	/*
	 * 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.
	 */
	if (parse->hasJoinRTEs)
		expr = flatten_join_alias_vars(parse, expr);

	/*
	 * Simplify constant expressions.
	 *
	 * 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(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 (parse->hasSubLinks)
		expr = SS_process_sublinks(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 */
	if (PlannerQueryLevel > 1)
		expr = SS_replace_correlation_vars(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(Query *parse, 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(parse, lfirst(l));

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

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

		j->quals = preprocess_expression(parse, 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.  (This is not so critical for DELETE, but for simplicity we treat
 * inherited DELETE the same way.)	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.
 *
 * parse is the querytree produced by the parser & rewriter.
 * inheritlist is an integer list of RT indexes for the result relation set.
 *
 * Returns a query plan.
 *--------------------
 */
static Plan *
inheritance_planner(Query *parse, List *inheritlist)
{
	int			parentRTindex = parse->resultRelation;
	Oid			parentOID = getrelid(parentRTindex, parse->rtable);
	int			mainrtlength = list_length(parse->rtable);
	List	   *subplans = NIL;
	List	   *tlist = NIL;
	ListCell   *l;

	foreach(l, inheritlist)
	{
		int			childRTindex = lfirst_int(l);
		Oid			childOID = getrelid(childRTindex, parse->rtable);
		Query	   *subquery;
		Plan	   *subplan;

		/* Generate modified query with this rel as target */
		subquery = (Query *) adjust_inherited_attrs((Node *) parse,
												parentRTindex, parentOID,
												 childRTindex, childOID);
		/* Generate plan */
		subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */ );
		subplans = lappend(subplans, subplan);

		/*
		 * XXX my goodness this next bit is ugly.  Really need to think about
		 * ways to rein in planner's habit of scribbling on its input.
		 *
		 * Planning of the subquery might have modified the rangetable,
		 * either by addition of RTEs due to expansion of inherited source
		 * tables, or by changes of the Query structures inside subquery
		 * RTEs.  We have to ensure that this gets propagated back to the
		 * master copy.  However, if we aren't done planning yet, we also
		 * need to ensure that subsequent calls to grouping_planner have
		 * virgin sub-Queries to work from.  So, if we are at the last
		 * list entry, just copy the subquery rangetable back to the master
		 * copy; if we are not, then extend the master copy by adding
		 * whatever the subquery added.  (We assume these added entries
		 * will go untouched by the future grouping_planner calls.  We are
		 * also 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.  Did I say this is ugly?)
		 */
		if (lnext(l) == NULL)
			parse->rtable = subquery->rtable;
		else
		{
			int		subrtlength = list_length(subquery->rtable);

			if (subrtlength > mainrtlength)
			{
				List	   *subrt;

				subrt = list_copy_tail(subquery->rtable, mainrtlength);
				parse->rtable = list_concat(parse->rtable, subrt);
				mainrtlength = subrtlength;
			}
		}

		/* Save preprocessed tlist from first rel for use in Append */
		if (tlist == NIL)
			tlist = subplan->targetlist;
	}

	/* Save the target-relations list for the executor, too */
	parse->resultRelations = inheritlist;

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

	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.
 *
 * parse is the querytree produced by the parser & rewriter.
 * 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, parse->query_pathkeys is returned as the
 * actual output ordering of the plan (in pathkey format).
 *--------------------
 */
static Plan *
grouping_planner(Query *parse, double tuple_fraction)
{
	List	   *tlist = parse->targetList;
	Plan	   *result_plan;
	List	   *current_pathkeys;
	List	   *sort_pathkeys;

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

		/*
		 * Construct the plan for set operations.  The result will not
		 * need any work except perhaps a top-level sort and/or LIMIT.
		 */
		result_plan = plan_set_operations(parse,
										  &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(set_sortclauses,
												result_plan->targetlist);
		current_pathkeys = canonicalize_pathkeys(parse, current_pathkeys);

		/*
		 * 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(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
		 */
		sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
													  tlist);
		sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
	}
	else
	{
		/* No set operations, do regular planning */
		List	   *sub_tlist;
		List	   *group_pathkeys;
		AttrNumber *groupColIdx = NULL;
		bool		need_tlist_eval = true;
		QualCost	tlist_cost;
		double		sub_tuple_fraction;
		Path	   *cheapest_path;
		Path	   *sorted_path;
		Path	   *best_path;
		double		dNumGroups = 0;
		long		numGroups = 0;
		AggClauseCounts agg_counts;
		int			numGroupCols = list_length(parse->groupClause);
		bool		use_hashed_grouping = false;

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

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

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

		/*
		 * Calculate pathkeys that represent grouping/ordering
		 * requirements
		 */
		group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause,
													   tlist);
		sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
													  tlist);

		/*
		 * 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 need a sorted result from query_planner.
		 *
		 * If we have a GROUP BY clause, then we want a result sorted
		 * properly for grouping.  Otherwise, if there is an ORDER BY
		 * clause, we want to sort by the ORDER BY clause.	(Note: if we
		 * have both, 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...)
		 */
		if (parse->groupClause)
			parse->query_pathkeys = group_pathkeys;
		else if (parse->sortClause)
			parse->query_pathkeys = sort_pathkeys;
		else
			parse->query_pathkeys = NIL;

		/*
		 * Adjust tuple_fraction if we see that we are going to apply
		 * limiting/grouping/aggregation/etc.  This is not overridable by
		 * the caller, since it reflects plan actions that this routine
		 * will certainly take, not assumptions about context.
		 */
		if (parse->limitCount != NULL)
		{
			/*
			 * A LIMIT clause limits the absolute number of tuples
			 * returned. However, if it's not a constant LIMIT then we
			 * have to punt; for lack of a better idea, assume 10% of the
			 * plan's result is wanted.
			 */
			double		limit_fraction = 0.0;

			if (IsA(parse->limitCount, Const))
			{
				Const	   *limitc = (Const *) parse->limitCount;
				int32		count = DatumGetInt32(limitc->constvalue);

				/*
				 * A NULL-constant LIMIT represents "LIMIT ALL", which we
				 * treat the same as no limit (ie, expect to retrieve all
				 * the tuples).
				 */
				if (!limitc->constisnull && count > 0)
				{
					limit_fraction = (double) count;
					/* We must also consider the OFFSET, if present */
					if (parse->limitOffset != NULL)
					{
						if (IsA(parse->limitOffset, Const))
						{
							int32		offset;

							limitc = (Const *) parse->limitOffset;
							offset = DatumGetInt32(limitc->constvalue);
							if (!limitc->constisnull && offset > 0)
								limit_fraction += (double) offset;
						}
						else
						{
							/* OFFSET is an expression ... punt ... */
							limit_fraction = 0.10;
						}
					}
				}
			}
			else
			{
				/* LIMIT is an expression ... punt ... */
				limit_fraction = 0.10;
			}

			if (limit_fraction > 0.0)
			{
				/*
				 * If we have absolute limits from both caller and LIMIT,
				 * use the smaller value; if one is fractional and the
				 * other absolute, treat the fraction as a fraction of the
				 * absolute value; else we can multiply the two fractions
				 * together.
				 */
				if (tuple_fraction >= 1.0)
				{
					if (limit_fraction >= 1.0)
					{
						/* both absolute */
						tuple_fraction = Min(tuple_fraction, limit_fraction);
					}
					else
					{
						/* caller absolute, limit fractional */
						tuple_fraction *= limit_fraction;
						if (tuple_fraction < 1.0)
							tuple_fraction = 1.0;
					}
				}
				else if (tuple_fraction > 0.0)
				{
					if (limit_fraction >= 1.0)
					{
						/* caller fractional, limit absolute */
						tuple_fraction *= limit_fraction;
						if (tuple_fraction < 1.0)
							tuple_fraction = 1.0;
					}
					else
					{
						/* both fractional */
						tuple_fraction *= limit_fraction;
					}
				}
				else
				{
					/* no info from caller, just use limit */
					tuple_fraction = limit_fraction;
				}
			}
		}

		/*
		 * With grouping or aggregation, the tuple fraction to pass to
		 * query_planner() may be different from what it is at top level.
		 */
		sub_tuple_fraction = tuple_fraction;

		if (parse->groupClause)
		{
			/*
			 * In GROUP BY mode, we have the little problem that we don't
			 * really know how many input tuples will be needed to make a
			 * group, so we can't translate an output LIMIT count into an
			 * input count.  For lack of a better idea, assume 25% of the
			 * input data will be processed if there is any output limit.
			 * However, if the caller gave us a fraction rather than an
			 * absolute count, we can keep using that fraction (which
			 * amounts to assuming that all the groups are about the same
			 * size).
			 */
			if (sub_tuple_fraction >= 1.0)
				sub_tuple_fraction = 0.25;

			/*
			 * If both GROUP BY and ORDER BY are specified, we will need
			 * two levels of sort --- and, therefore, certainly need to
			 * read all the input tuples --- unless ORDER BY is a subset
			 * of GROUP BY.  (We have not yet canonicalized the pathkeys,
			 * so must use the slower noncanonical comparison method.)
			 */
			if (parse->groupClause && parse->sortClause &&
				!noncanonical_pathkeys_contained_in(sort_pathkeys,
													group_pathkeys))
				sub_tuple_fraction = 0.0;
		}
		else if (parse->hasAggs)
		{
			/*
			 * Ungrouped aggregate will certainly want all the input
			 * tuples.
			 */
			sub_tuple_fraction = 0.0;
		}
		else if (parse->distinctClause)
		{
			/*
			 * SELECT DISTINCT, like GROUP, will absorb an unpredictable
			 * number of input tuples per output tuple.  Handle the same
			 * way.
			 */
			if (sub_tuple_fraction >= 1.0)
				sub_tuple_fraction = 0.25;
		}

		/*
		 * Generate the best unsorted and presorted paths for this Query
		 * (but note there may not be any presorted path).
		 */
		query_planner(parse, sub_tlist, sub_tuple_fraction,
					  &cheapest_path, &sorted_path);

		/*
		 * We couldn't canonicalize group_pathkeys and sort_pathkeys
		 * before running query_planner(), so do it now.
		 */
		group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys);
		sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);

		/*
		 * If grouping, estimate the number of groups.  (We can't do this
		 * until after running query_planner(), either.)  Then decide
		 * whether we want to use hashed grouping.
		 */
		if (parse->groupClause)
		{
			List	   *groupExprs;
			double		cheapest_path_rows;

			/*
			 * Beware 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;
			else
				cheapest_path_rows = 1; /* assume non-set result */

			groupExprs = get_sortgrouplist_exprs(parse->groupClause,
												 parse->targetList);
			dNumGroups = estimate_num_groups(parse,
											 groupExprs,
											 cheapest_path_rows);
			/* Also want it as a long int --- but 'ware overflow! */
			numGroups = (long) Min(dNumGroups, (double) LONG_MAX);

			use_hashed_grouping =
				choose_hashed_grouping(parse, tuple_fraction,
									   cheapest_path, sorted_path,
									   sort_pathkeys, group_pathkeys,
									   dNumGroups, &agg_counts);
		}

		/*
		 * 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(parse,
												 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.
			 */
			result_plan = create_plan(parse, best_path);
			current_pathkeys = best_path->pathkeys;

			/*
			 * 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(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 and
				 * Group project new tlists (the rest just copy their input
				 * tuples) --- so make_agg() and make_group() are responsible
				 * for computing the added cost.
				 */
				cost_qual_eval(&tlist_cost, sub_tlist);
				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(parse, 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(parse,
												tlist,
												(List *) parse->havingQual,
												AGG_HASHED,
												numGroupCols,
												groupColIdx,
												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 (!pathkeys_contained_in(group_pathkeys,
											   current_pathkeys))
					{
						result_plan = (Plan *)
							make_sort_from_groupcols(parse,
													 parse->groupClause,
													 groupColIdx,
													 result_plan);
						current_pathkeys = 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(parse,
												tlist,
												(List *) parse->havingQual,
												aggstrategy,
												numGroupCols,
												groupColIdx,
												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 (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
				{
					result_plan = (Plan *)
						make_sort_from_groupcols(parse,
												 parse->groupClause,
												 groupColIdx,
												 result_plan);
					current_pathkeys = group_pathkeys;
				}

				result_plan = (Plan *) make_group(parse,
												  tlist,
												  (List *) parse->havingQual,
												  numGroupCols,
												  groupColIdx,
												  dNumGroups,
												  result_plan);
				/* The Group node won't change sort ordering */
			}
			else if (parse->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(tlist,
												   parse->havingQual,
												   NULL);
			}
		}						/* end of non-minmax-aggregate case */
	}							/* end of if (setOperations) */

	/*
	 * If 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(sort_pathkeys, current_pathkeys))
		{
			result_plan = (Plan *)
				make_sort_from_sortclauses(parse,
										   parse->sortClause,
										   result_plan);
			current_pathkeys = sort_pathkeys;
		}
	}

	/*
	 * If there is a DISTINCT clause, add the UNIQUE node.
	 */
	if (parse->distinctClause)
	{
		result_plan = (Plan *) make_unique(result_plan, parse->distinctClause);

		/*
		 * If there was grouping or aggregation, leave plan_rows as-is
		 * (ie, assume the result was already mostly unique).  If not,
		 * it's reasonable to assume the UNIQUE filter has effects
		 * comparable to GROUP BY.
		 */
		if (!parse->groupClause && !parse->hasHavingQual && !parse->hasAggs)
		{
			List	   *distinctExprs;

			distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
													parse->targetList);
			result_plan->plan_rows = estimate_num_groups(parse,
														 distinctExprs,
												 result_plan->plan_rows);
		}
	}

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

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

	return result_plan;
}

/*
 * choose_hashed_grouping - should we use hashed grouping?
 */
static bool
choose_hashed_grouping(Query *parse, double tuple_fraction,
					   Path *cheapest_path, Path *sorted_path,
					   List *sort_pathkeys, List *group_pathkeys,
					   double dNumGroups, AggClauseCounts *agg_counts)
{
	int			numGroupCols = list_length(parse->groupClause);
	double		cheapest_path_rows;
	int			cheapest_path_width;
	Size		hashentrysize;
	List	   *current_pathkeys;
	Path		hashed_p;
	Path		sorted_p;

	/*
	 * Check can't-do-it conditions, including whether the grouping operators
	 * are hashjoinable.
	 *
	 * 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.)
	 */
	if (!enable_hashagg)
		return false;
	if (agg_counts->numDistinctAggs != 0)
		return false;
	if (!hash_safe_grouping(parse))
		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 = cheapest_path_width;
	/* 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;

	/*
	 * 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, parse, 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 (sort_pathkeys)
		cost_sort(&hashed_p, parse, sort_pathkeys, hashed_p.total_cost,
				  dNumGroups, cheapest_path_width);

	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(group_pathkeys,
							   current_pathkeys))
	{
		cost_sort(&sorted_p, parse, group_pathkeys, sorted_p.total_cost,
				  cheapest_path_rows, cheapest_path_width);
		current_pathkeys = group_pathkeys;
	}

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

	/*
	 * 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;
}

/*
 * hash_safe_grouping - are grouping operators hashable?
 *
 * We assume hashed aggregation will work if the datatype's equality operator
 * is marked hashjoinable.
 */
static bool
hash_safe_grouping(Query *parse)
{
	ListCell   *gl;

	foreach(gl, parse->groupClause)
	{
		GroupClause *grpcl = (GroupClause *) lfirst(gl);
		TargetEntry *tle = get_sortgroupclause_tle(grpcl, parse->targetList);
		Operator	optup;
		bool		oprcanhash;

		optup = equality_oper(exprType((Node *) tle->expr), true);
		if (!optup)
			return false;
		oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash;
		ReleaseSysCache(optup);
		if (!oprcanhash)
			return false;
	}
	return true;
}

/*---------------
 * 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
 * replace_vars_with_subplan_refs() 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.
 *
 * 'parse' is the query being processed.
 * '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(Query *parse,
					   List *tlist,
					   AttrNumber **groupColIdx,
					   bool *need_tlist_eval)
{
	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 && !parse->hasHavingQual)
	{
		*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).
	 */
	sub_tlist = flatten_tlist(tlist);
	extravars = pull_var_clause(parse->havingQual, false);
	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)
		{
			GroupClause *grpcl = (GroupClause *) lfirst(gl);
			Node	   *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
			TargetEntry *te = NULL;
			ListCell   *sl;

			/* Find or make a matching sub_tlist entry */
			foreach(sl, sub_tlist)
			{
				te = (TargetEntry *) lfirst(sl);
				if (equal(groupexpr, te->expr))
					break;
			}
			if (!sl)
			{
				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 vars in the real sub_tlist.
 */
static void
locate_grouping_columns(Query *parse,
						List *tlist,
						List *sub_tlist,
						AttrNumber *groupColIdx)
{
	int			keyno = 0;
	ListCell   *gl;

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

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

		foreach(sl, sub_tlist)
		{
			te = (TargetEntry *) lfirst(sl);
			if (equal(groupexpr, te->expr))
				break;
		}
		if (!sl)
			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;
}
