postgres/src/backend/optimizer/plan/planner.c

/*-------------------------------------------------------------------------
 *
 * planner.c
 *	  The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.172 2004/06/11 01:08:52 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>

#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "executor/executor.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/analyze.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 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;
			}
		}
	}

	/*
	 * 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);
	}

	/*
	 * A HAVING clause without aggregates is equivalent to a WHERE clause
	 * (except it can only refer to grouped fields).  Transfer any
	 * agg-free clauses of the HAVING qual into WHERE.	This may seem like
	 * wasting cycles to cater to stupidly-written queries, but there are
	 * other reasons for doing it.	Firstly, if the query contains no aggs
	 * at all, then we aren't going to generate an Agg plan node, and so
	 * there'll be no place to execute HAVING conditions; without this
	 * transfer, we'd lose the HAVING condition entirely, which is wrong.
	 * Secondly, when we push down a qual condition into a sub-query, it's
	 * easiest to push the qual into HAVING always, in case it contains
	 * aggs, and then let this code sort it out.
	 *
	 * 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))
			newHaving = lappend(newHaving, havingclause);
		else
			parse->jointree->quals = (Node *)
				lappend((List *) parse->jointree->quals, 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,
										false)) != 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.
	 */
	if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
	{
		Cost		initplan_cost = 0;

		/* Prepare extParam/allParam sets for all nodes in tree */
		SS_finalize_plan(plan, parse->rtable);

		/*
		 * SS_finalize_plan doesn't handle initPlans, so we have to
		 * manually attach them to the topmost plan node, and add their
		 * extParams to the topmost node's, too.
		 *
		 * We also add the total_cost of each initPlan to the startup cost of
		 * the top node.  This is a conservative overestimate, since in
		 * fact each initPlan might be executed later than plan startup,
		 * or even not at all.
		 */
		plan->initPlan = PlannerInitPlan;

		foreach(l, plan->initPlan)
		{
			SubPlan    *initplan = (SubPlan *) lfirst(l);

			plan->extParam = bms_add_members(plan->extParam,
											 initplan->plan->extParam);
			/* allParam must include all members of extParam */
			plan->allParam = bms_add_members(plan->allParam,
											 plan->extParam);
			initplan_cost += initplan->plan->total_cost;
		}

		plan->startup_cost += initplan_cost;
		plan->total_cost += initplan_cost;
	}

	/* 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);

	/*
	 * If it's a qual or havingQual, canonicalize it.  It seems most useful
	 * to do this before applying eval_const_expressions, since the latter
	 * can optimize flattened AND/ORs better than unflattened ones.
	 *
	 * Note: 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.
	 */
	if (kind == EXPRKIND_QUAL)
	{
		expr = (Node *) canonicalize_qual((Expr *) expr);

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

	/*
	 * Simplify constant expressions.
	 */
	expr = eval_const_expressions(expr);

	/* 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);
		int			subrtlength;
		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);

		/*
		 * It's possible that additional RTEs got added to the rangetable
		 * due to expansion of inherited source tables (see allpaths.c).
		 * If so, we must copy 'em back to the main parse tree's rtable.
		 *
		 * XXX my goodness this is ugly.  Really need to think about ways to
		 * rein in planner's habit of scribbling on its input.
		 */
		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 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 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;
		double		dNumGroups = 0;
		long		numGroups = 0;
		int			numAggs = 0;
		int			numGroupCols = list_length(parse->groupClause);
		bool		use_hashed_grouping = false;

		/* Preprocess targetlist in case we are inside an INSERT/UPDATE. */
		tlist = preprocess_targetlist(tlist,
									  parse->commandType,
									  parse->resultRelation,
									  parse->rtable);

		/*
		 * Add TID targets for rels selected FOR UPDATE (should this be
		 * done in preprocess_targetlist?).  The executor uses the TID to
		 * know which rows to lock, much as for UPDATE or DELETE.
		 */
		if (parse->rowMarks)
		{
			ListCell   *l;

			/*
			 * We've got trouble if the FOR UPDATE appears inside
			 * grouping, since grouping renders a reference to individual
			 * tuple CTIDs invalid.  This is also checked at parse time,
			 * but that's insufficient because of rule substitution, query
			 * pullup, etc.
			 */
			CheckSelectForUpdate(parse);

			/*
			 * Currently the executor only supports FOR UPDATE at top
			 * level
			 */
			if (PlannerQueryLevel > 1)
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
						 errmsg("SELECT FOR UPDATE is not allowed in subqueries")));

			foreach(l, parse->rowMarks)
			{
				Index		rti = lfirst_int(l);
				char	   *resname;
				Resdom	   *resdom;
				Var		   *var;
				TargetEntry *ctid;

				resname = (char *) palloc(32);
				snprintf(resname, 32, "ctid%u", rti);
				resdom = makeResdom(list_length(tlist) + 1,
									TIDOID,
									-1,
									resname,
									true);

				var = makeVar(rti,
							  SelfItemPointerAttributeNumber,
							  TIDOID,
							  -1,
							  0);

				ctid = makeTargetEntry(resdom, (Expr *) var);
				tlist = lappend(tlist, ctid);
			}
		}

		/*
		 * 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)
			numAggs = count_agg_clause((Node *) tlist) +
				count_agg_clause(parse->havingQual);

		/*
		 * 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);

		/*
		 * Consider whether we might want to use hashed grouping.
		 */
		if (parse->groupClause)
		{
			List	   *groupExprs;
			double		cheapest_path_rows;
			int			cheapest_path_width;

			/*
			 * Beware in this section 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 */
			}

			/*
			 * Always estimate the number of groups.  We can't do this
			 * until after running query_planner(), either.
			 */
			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);

			/*
			 * 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 || !hash_safe_grouping(parse))
				use_hashed_grouping = false;
			else if (parse->hasAggs &&
					 (contain_distinct_agg_clause((Node *) tlist) ||
					  contain_distinct_agg_clause(parse->havingQual)))
				use_hashed_grouping = false;
			else
			{
				/*
				 * Use hashed grouping if (a) we think we can fit the
				 * hashtable into work_mem, *and* (b) 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.
				 *
				 * In most cases we have no good way to estimate the size of
				 * the transition value needed by an aggregate;
				 * arbitrarily assume it is 100 bytes.	Also set the
				 * overhead per hashtable entry at 64 bytes.
				 */
				int			hashentrysize = cheapest_path_width + 64 + numAggs * 100;

				if (hashentrysize * dNumGroups <= work_mem * 1024L)
				{
					/*
					 * Okay, do the 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.
					 */
					Path		hashed_p;
					Path		sorted_p;

					cost_agg(&hashed_p, parse,
							 AGG_HASHED, 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, 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 */
						use_hashed_grouping = true;
					}
				}
			}
		}

		/*
		 * Select the best path and create a plan to execute it.
		 *
		 * 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 (sorted_path && !use_hashed_grouping)
		{
			result_plan = create_plan(parse, sorted_path);
			current_pathkeys = sorted_path->pathkeys;
		}
		else
		{
			result_plan = create_plan(parse, cheapest_path);
			current_pathkeys = cheapest_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 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,
											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,
											numAggs,
											result_plan);
		}
		else
		{
			/*
			 * If there are no Aggs, we shouldn't have any HAVING qual
			 * anymore
			 */
			Assert(parse->havingQual == NULL);

			/*
			 * If we have a GROUP BY clause, insert a group node (plus the
			 * appropriate sort node, if necessary).
			 */
			if (parse->groupClause)
			{
				/*
				 * 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,
												  numGroupCols,
												  groupColIdx,
												  dNumGroups,
												  result_plan);
				/* The Group node won't change sort ordering */
			}
		}
	}							/* 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->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;
}

/*
 * 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(tle->resdom->restype, 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 or Group 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, if we are doing either
 * grouping or aggregation, 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, nothing to do here;
	 * query_planner should receive the unmodified target list.
	 */
	if (!parse->hasAggs && !parse->groupClause)
	{
		*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(makeResdom(list_length(sub_tlist) + 1,
												exprType(groupexpr),
												exprTypmod(groupexpr),
												NULL,
												false),
									 (Expr *) groupexpr);
				sub_tlist = lappend(sub_tlist, te);
				*need_tlist_eval = true;		/* it's not flat anymore */
			}

			/* and save its resno */
			grpColIdx[keyno++] = te->resdom->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->resdom->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->resdom->resjunk)
			continue;

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