[postgresql] / src / backend / optimizer / plan / planner.c

/*-------------------------------------------------------------------------
 *
 * planner.c
 *        The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.101 2001/01/27 04:42:32 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "catalog/pg_type.h"
#include "nodes/makefuncs.h"
#include "optimizer/clauses.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 "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"


/* Expression kind codes for preprocess_expression */
#define EXPRKIND_TARGET 0
#define EXPRKIND_WHERE  1
#define EXPRKIND_HAVING 2


static Node *pull_up_subqueries(Query *parse, Node *jtnode);
static bool is_simple_subquery(Query *subquery);
static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist);
static Node *preprocess_jointree(Query *parse, Node *jtnode);
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 List *make_subplanTargetList(Query *parse, List *tlist,
                                           AttrNumber **groupColIdx);
static Plan *make_groupplan(List *group_tlist, bool tuplePerGroup,
                           List *groupClause, AttrNumber *grpColIdx,
                           bool is_presorted, Plan *subplan);
static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);


/*****************************************************************************
 *
 *         Query optimizer entry point
 *
 *****************************************************************************/
Plan *
planner(Query *parse)
{
        Plan       *result_plan;
        Index           save_PlannerQueryLevel;
        List       *save_PlannerParamVar;

        /*
         * 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.
         *
         * These vars cannot be moved into the Query structure since their
         * whole purpose is communication across multiple sub-Queries.
         *
         * 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_PlannerParamVar = PlannerParamVar;

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

        /* primary planning entry point (may recurse for subqueries) */
        result_plan = subquery_planner(parse, -1.0 /* default case */ );

        Assert(PlannerQueryLevel == 0);

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

        /* final cleanup of the plan */
        set_plan_references(result_plan);

        /* restore state for outer planner, if any */
        PlannerQueryLevel = save_PlannerQueryLevel;
        PlannerParamVar = save_PlannerParamVar;

        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;
        Plan       *plan;
        List       *newHaving;
        List       *lst;

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

#ifdef ENABLE_KEY_SET_QUERY
        /* this should go away sometime soon */
        transformKeySetQuery(parse);
#endif

        /*
         * 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);
        /*
         * If so, we may have created opportunities to simplify the jointree.
         */
        parse->jointree = (FromExpr *)
                preprocess_jointree(parse, (Node *) parse->jointree);

        /*
         * 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_HAVING);

        /*
         * 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 *.  Also note that contain_agg_clause does not
         * recurse into sub-selects, which is exactly what we need here.
         */
        newHaving = NIL;
        foreach(lst, (List *) parse->havingQual)
        {
                Node   *havingclause = (Node *) lfirst(lst);

                if (contain_agg_clause(havingclause))
                        newHaving = lappend(newHaving, havingclause);
                else
                        parse->jointree->quals = (Node *)
                                lappend((List *) parse->jointree->quals, havingclause);
        }
        parse->havingQual = (Node *) newHaving;

        /*
         * 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_inherted_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 subPlan, extParam and locParam lists for plan nodes.
         */
        if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
        {
                (void) SS_finalize_plan(plan);
                /*
                 * At the moment, SS_finalize_plan doesn't handle initPlans
                 * and so we assign them to the topmost plan node.
                 */
                plan->initPlan = PlannerInitPlan;
                /* Must add the initPlans' extParams to the topmost node's, too */
                foreach(lst, plan->initPlan)
                {
                        SubPlan *subplan = (SubPlan *) lfirst(lst);

                        plan->extParam = set_unioni(plan->extParam,
                                                                                subplan->plan->extParam);
                }
        }

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

        return plan;
}

/*
 * pull_up_subqueries
 *              Look for subqueries in the rangetable that can be pulled up into
 *              the parent query.  If the subquery has no special features like
 *              grouping/aggregation then we can merge it into the parent's jointree.
 *
 * A tricky aspect of this code is that if we pull up a subquery we have
 * to replace Vars that reference the subquery's outputs throughout the
 * parent query, including quals attached to jointree nodes above the one
 * we are currently processing!  We handle this by being careful not to
 * change the jointree structure while recursing: no nodes other than
 * subquery RangeTblRef entries will be replaced.  Also, we can't turn
 * ResolveNew loose on the whole jointree, because it'll return a mutated
 * copy of the tree; we have to invoke it just on the quals, instead.
 */
static Node *
pull_up_subqueries(Query *parse, Node *jtnode)
{
        if (jtnode == NULL)
                return NULL;
        if (IsA(jtnode, RangeTblRef))
        {
                int                     varno = ((RangeTblRef *) jtnode)->rtindex;
                RangeTblEntry *rte = rt_fetch(varno, parse->rtable);
                Query      *subquery = rte->subquery;

                /*
                 * Is this a subquery RTE, and if so, is the subquery simple enough
                 * to pull up?  (If not, do nothing at this node.)
                 */
                if (subquery && is_simple_subquery(subquery))
                {
                        int             rtoffset;
                        Node   *subjointree;
                        List   *subtlist;
                        List   *l;

                        /*
                         * First, recursively pull up the subquery's subqueries,
                         * so that this routine's processing is complete for its
                         * jointree and rangetable.  NB: if the same subquery is
                         * referenced from multiple jointree items (which can't happen
                         * normally, but might after rule rewriting), then we will invoke
                         * this processing multiple times on that subquery.  OK because
                         * nothing will happen after the first time.  We do have to be
                         * careful to copy everything we pull up, however, or risk
                         * having chunks of structure multiply linked.
                         */
                        subquery->jointree = (FromExpr *)
                                pull_up_subqueries(subquery, (Node *) subquery->jointree);
                        /*
                         * Append the subquery's rangetable to mine (currently,
                         * no adjustments will be needed in the subquery's rtable).
                         */
                        rtoffset = length(parse->rtable);
                        parse->rtable = nconc(parse->rtable,
                                                                  copyObject(subquery->rtable));
                        /*
                         * Make copies of the subquery's jointree and targetlist
                         * with varnos adjusted to match the merged rangetable.
                         */
                        subjointree = copyObject(subquery->jointree);
                        OffsetVarNodes(subjointree, rtoffset, 0);
                        subtlist = copyObject(subquery->targetList);
                        OffsetVarNodes((Node *) subtlist, rtoffset, 0);
                        /*
                         * Replace all of the top query's references to the subquery's
                         * outputs with copies of the adjusted subtlist items, being
                         * careful not to replace any of the jointree structure.
                         */
                        parse->targetList = (List *)
                                ResolveNew((Node *) parse->targetList,
                                                   varno, 0, subtlist, CMD_SELECT, 0);
                        resolvenew_in_jointree((Node *) parse->jointree, varno, subtlist);
                        parse->havingQual =
                                ResolveNew(parse->havingQual,
                                                   varno, 0, subtlist, CMD_SELECT, 0);
                        /*
                         * Pull up any FOR UPDATE markers, too.
                         */
                        foreach(l, subquery->rowMarks)
                        {
                                int             submark = lfirsti(l);

                                parse->rowMarks = lappendi(parse->rowMarks,
                                                                                   submark + rtoffset);
                        }
                        /*
                         * Miscellaneous housekeeping.
                         */
                        parse->hasSubLinks |= subquery->hasSubLinks;
                        /* subquery won't be pulled up if it hasAggs, so no work there */

                        /*
                         * Return the adjusted subquery jointree to replace the
                         * RangeTblRef entry in my jointree.
                         */
                        return subjointree;
                }
        }
        else if (IsA(jtnode, FromExpr))
        {
                FromExpr   *f = (FromExpr *) jtnode;
                List       *l;

                foreach(l, f->fromlist)
                {
                        lfirst(l) = pull_up_subqueries(parse, lfirst(l));
                }
        }
        else if (IsA(jtnode, JoinExpr))
        {
                JoinExpr   *j = (JoinExpr *) jtnode;

                j->larg = pull_up_subqueries(parse, j->larg);
                j->rarg = pull_up_subqueries(parse, j->rarg);
        }
        else
                elog(ERROR, "pull_up_subqueries: unexpected node type %d",
                         nodeTag(jtnode));
        return jtnode;
}

/*
 * is_simple_subquery
 *        Check a subquery in the range table to see if it's simple enough
 *        to pull up into the parent query.
 */
static bool
is_simple_subquery(Query *subquery)
{
        /*
         * Let's just make sure it's a valid subselect ...
         */
        if (!IsA(subquery, Query) ||
                subquery->commandType != CMD_SELECT ||
                subquery->resultRelation != 0 ||
                subquery->into != NULL ||
                subquery->isPortal)
                elog(ERROR, "is_simple_subquery: subquery is bogus");
        /*
         * Can't currently pull up a query with setops.
         * Maybe after querytree redesign...
         */
        if (subquery->setOperations)
                return false;
        /*
         * Can't pull up a subquery involving grouping, aggregation, sorting,
         * or limiting.
         */
        if (subquery->hasAggs ||
                subquery->groupClause ||
                subquery->havingQual ||
                subquery->sortClause ||
                subquery->distinctClause ||
                subquery->limitOffset ||
                subquery->limitCount)
                return false;
        /*
         * Hack: don't try to pull up a subquery with an empty jointree.
         * query_planner() will correctly generate a Result plan for a
         * jointree that's totally empty, but I don't think the right things
         * happen if an empty FromExpr appears lower down in a jointree.
         * Not worth working hard on this, just to collapse SubqueryScan/Result
         * into Result...
         */
        if (subquery->jointree->fromlist == NIL)
                return false;

        return true;
}

/*
 * Helper routine for pull_up_subqueries: do ResolveNew on every expression
 * in the jointree, without changing the jointree structure itself.  Ugly,
 * but there's no other way...
 */
static void
resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist)
{
        if (jtnode == NULL)
                return;
        if (IsA(jtnode, RangeTblRef))
        {
                /* nothing to do here */
        }
        else if (IsA(jtnode, FromExpr))
        {
                FromExpr   *f = (FromExpr *) jtnode;
                List       *l;

                foreach(l, f->fromlist)
                        resolvenew_in_jointree(lfirst(l), varno, subtlist);
                f->quals = ResolveNew(f->quals,
                                                          varno, 0, subtlist, CMD_SELECT, 0);
        }
        else if (IsA(jtnode, JoinExpr))
        {
                JoinExpr   *j = (JoinExpr *) jtnode;

                resolvenew_in_jointree(j->larg, varno, subtlist);
                resolvenew_in_jointree(j->rarg, varno, subtlist);
                j->quals = ResolveNew(j->quals,
                                                          varno, 0, subtlist, CMD_SELECT, 0);
                /* We don't bother to update the colvars list, since it won't be
                 * used again ...
                 */
        }
        else
                elog(ERROR, "resolvenew_in_jointree: unexpected node type %d",
                         nodeTag(jtnode));
}

/*
 * preprocess_jointree
 *              Attempt to simplify a query's jointree.
 *
 * If we succeed in pulling up a subquery then we might form a jointree
 * in which a FromExpr is a direct child of another FromExpr.  In that
 * case we can consider collapsing the two FromExprs into one.  This is
 * an optional conversion, since the planner will work correctly either
 * way.  But we may find a better plan (at the cost of more planning time)
 * if we merge the two nodes.
 *
 * NOTE: don't try to do this in the same jointree scan that does subquery
 * pullup!  Since we're changing the jointree structure here, that wouldn't
 * work reliably --- see comments for pull_up_subqueries().
 */
static Node *
preprocess_jointree(Query *parse, Node *jtnode)
{
        if (jtnode == NULL)
                return NULL;
        if (IsA(jtnode, RangeTblRef))
        {
                /* nothing to do here... */
        }
        else if (IsA(jtnode, FromExpr))
        {
                FromExpr   *f = (FromExpr *) jtnode;
                List       *newlist = NIL;
                List       *l;

                foreach(l, f->fromlist)
                {
                        Node   *child = (Node *) lfirst(l);

                        /* Recursively simplify the child... */
                        child = preprocess_jointree(parse, child);
                        /* Now, is it a FromExpr? */
                        if (child && IsA(child, FromExpr))
                        {
                                /*
                                 * Yes, so do we want to merge it into parent?  Always do so
                                 * if child has just one element (since that doesn't make the
                                 * parent's list any longer).  Otherwise we have to be careful
                                 * about the increase in planning time caused by combining the
                                 * two join search spaces into one.  Our heuristic is to merge
                                 * if the merge will produce a join list no longer than
                                 * GEQO_RELS/2.  (Perhaps need an additional user parameter?)
                                 */
                                FromExpr   *subf = (FromExpr *) child;
                                int                     childlen = length(subf->fromlist);
                                int                     myothers = length(newlist) + length(lnext(l));

                                if (childlen <= 1 || (childlen+myothers) <= geqo_rels/2)
                                {
                                        newlist = nconc(newlist, subf->fromlist);
                                        f->quals = make_and_qual(f->quals, subf->quals);
                                }
                                else
                                        newlist = lappend(newlist, child);
                        }
                        else
                                newlist = lappend(newlist, child);
                }
                f->fromlist = newlist;
        }
        else if (IsA(jtnode, JoinExpr))
        {
                JoinExpr   *j = (JoinExpr *) jtnode;

                /* Can't usefully change the JoinExpr, but recurse on children */
                j->larg = preprocess_jointree(parse, j->larg);
                j->rarg = preprocess_jointree(parse, j->rarg);
        }
        else
                elog(ERROR, "preprocess_jointree: unexpected node type %d",
                         nodeTag(jtnode));
        return jtnode;
}

/*
 * 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)
{
        /*
         * Simplify constant expressions.
         *
         * Note that at this point quals have not yet been converted to
         * implicit-AND form, so we can apply eval_const_expressions directly.
         * Also note that we need to do this before SS_process_sublinks,
         * because that routine inserts bogus "Const" nodes.
         */
        expr = eval_const_expressions(expr);

        /*
         * If it's a qual or havingQual, canonicalize it, and convert it
         * to implicit-AND format.
         *
         * XXX Is there any value in re-applying eval_const_expressions after
         * canonicalize_qual?
         */
        if (kind != EXPRKIND_TARGET)
        {
                expr = (Node *) canonicalize_qual((Expr *) expr, true);

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

        if (parse->hasSubLinks)
        {
                /* Expand SubLinks to SubPlans */
                expr = SS_process_sublinks(expr);

                if (kind != EXPRKIND_WHERE &&
                        (parse->groupClause != NIL || parse->hasAggs))
                {
                        /*
                         * Check for ungrouped variables passed to subplans.  Note we
                         * do NOT do this for subplans in WHERE (or JOIN/ON); it's legal
                         * there because WHERE is evaluated pre-GROUP.
                         */
                        check_subplans_for_ungrouped_vars(expr, parse);
                }
        }

        /* Replace uplevel vars with Param nodes */
        if (PlannerQueryLevel > 1)
                expr = SS_replace_correlation_vars(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;
                List       *l;

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

                f->quals = preprocess_expression(parse, f->quals, EXPRKIND_WHERE);
        }
        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_WHERE);
        }
        else
                elog(ERROR, "preprocess_qual_conditions: unexpected node type %d",
                         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);
        List       *subplans = NIL;
        List       *tlist = NIL;
        List       *l;

        foreach(l, inheritlist)
        {
                int             childRTindex = lfirsti(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);
                /* 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;

        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: determine fraction by inspection of query (normal case)
 *        0: expect all tuples to be retrieved
 *        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)
 * The normal case is to pass -1, but some callers pass values >= 0 to
 * override this routine's determination of the appropriate fraction.
 *
 * Returns a query plan.
 *--------------------
 */
static Plan *
grouping_planner(Query *parse, double tuple_fraction)
{
        List       *tlist = parse->targetList;
        Plan       *result_plan;
        List       *current_pathkeys;
        List       *group_pathkeys;
        List       *sort_pathkeys;
        AttrNumber *groupColIdx = NULL;

        if (parse->setOperations)
        {
                /*
                 * 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);

                /*
                 * 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)
                        elog(ERROR, "SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT");

                /*
                 * We set current_pathkeys NIL indicating we do not know sort
                 * order.  This is correct when the top set operation is UNION ALL,
                 * since the appended-together results are unsorted even if the
                 * subplans were sorted.  For other set operations we could be
                 * smarter --- room for future improvement!
                 */
                current_pathkeys = NIL;

                /*
                 * Calculate pathkeys that represent grouping/ordering
                 * requirements (grouping should always be null, but...)
                 */
                group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause,
                                                                                                           tlist);
                sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
                                                                                                          tlist);
        }
        else
        {
                List       *sub_tlist;

                /* 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)
                {
                        List       *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)
                                elog(ERROR, "SELECT FOR UPDATE is not allowed in subselects");

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

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

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

                                ctid = makeTargetEntry(resdom, (Node *) 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);

                /*
                 * 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);

                /*
                 * 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;

                /*
                 * Figure out whether we expect to retrieve all the tuples that
                 * the plan can generate, or to stop early due to a LIMIT or other
                 * factors.  If the caller passed a value >= 0, believe that
                 * value, else do our own examination of the query context.
                 */
                if (tuple_fraction < 0.0)
                {
                        /* Initial assumption is we need all the tuples */
                        tuple_fraction = 0.0;

                        /*
                         * Check for a LIMIT clause.
                         */
                        if (parse->limitCount != NULL)
                        {
                                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)
                                        {
                                                tuple_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)
                                                                        tuple_fraction += (double) offset;
                                                        }
                                                        else
                                                        {
                                                                /* It's an expression ... punt ... */
                                                                tuple_fraction = 0.10;
                                                        }
                                                }
                                        }
                                }
                                else
                                {
                                        /*
                                         * COUNT is an expression ... don't know exactly what the
                                         * limit will be, but for lack of a better idea assume
                                         * 10% of the plan's result is wanted.
                                         */
                                        tuple_fraction = 0.10;
                                }
                        }

                        /*
                         * If no LIMIT, check for retrieve-into-portal, ie DECLARE CURSOR.
                         *
                         * 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?)
                         */
                        else if (parse->isPortal)
                                tuple_fraction = 0.10;
                }

                /*
                 * Adjust tuple_fraction if we see that we are going to apply
                 * 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->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 (tuple_fraction >= 1.0)
                                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))
                                tuple_fraction = 0.0;
                }
                else if (parse->hasAggs)
                {

                        /*
                         * Ungrouped aggregate will certainly want all the input
                         * tuples.
                         */
                        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 (tuple_fraction >= 1.0)
                                tuple_fraction = 0.25;
                }

                /* Generate the basic plan for this Query */
                result_plan = query_planner(parse,
                                                                        sub_tlist,
                                                                        tuple_fraction);

                /*
                 * query_planner returns actual sort order (which is not
                 * necessarily what we requested) in query_pathkeys.
                 */
                current_pathkeys = parse->query_pathkeys;
        }

        /*
         * 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 we have a GROUP BY clause, insert a group node (plus the
         * appropriate sort node, if necessary).
         */
        if (parse->groupClause)
        {
                bool            tuplePerGroup;
                List       *group_tlist;
                bool            is_sorted;

                /*
                 * Decide whether how many tuples per group the Group node needs
                 * to return. (Needs only one tuple per group if no aggregate is
                 * present. Otherwise, need every tuple from the group to do the
                 * aggregation.)  Note tuplePerGroup is named backwards :-(
                 */
                tuplePerGroup = parse->hasAggs;

                /*
                 * If there are aggregates then the Group node should just return
                 * the same set of vars as the subplan did (but we can exclude any
                 * GROUP BY expressions).  If there are no aggregates then the
                 * Group node had better compute the final tlist.
                 */
                if (parse->hasAggs)
                        group_tlist = flatten_tlist(result_plan->targetlist);
                else
                        group_tlist = tlist;

                /*
                 * Figure out whether the path result is already ordered the way
                 * we need it --- if so, no need for an explicit sort step.
                 */
                if (pathkeys_contained_in(group_pathkeys, current_pathkeys))
                {
                        is_sorted = true;       /* no sort needed now */
                        /* current_pathkeys remains unchanged */
                }
                else
                {

                        /*
                         * We will need to do an explicit sort by the GROUP BY clause.
                         * make_groupplan will do the work, but set current_pathkeys
                         * to indicate the resulting order.
                         */
                        is_sorted = false;
                        current_pathkeys = group_pathkeys;
                }

                result_plan = make_groupplan(group_tlist,
                                                                         tuplePerGroup,
                                                                         parse->groupClause,
                                                                         groupColIdx,
                                                                         is_sorted,
                                                                         result_plan);
        }

        /*
         * If aggregate is present, insert the Agg node
         *
         * HAVING clause, if any, becomes qual of the Agg node
         */
        if (parse->hasAggs)
        {
                result_plan = (Plan *) make_agg(tlist,
                                                                                (List *) parse->havingQual,
                                                                                result_plan);
                /* Note: Agg does not affect any existing sort order of the tuples */
        }
        else
        {
                /* If there are no Aggs, we shouldn't have any HAVING qual anymore */
                Assert(parse->havingQual == NULL);
        }

        /*
         * 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 = make_sortplan(tlist, result_plan,
                                                                                parse->sortClause);
        }

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

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

        return result_plan;
}

/*---------------
 * make_subplanTargetList
 *        Generate appropriate target list when grouping is required.
 *
 * When grouping_planner inserts Aggregate and/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
 * use only a+b, but it's not really worth the trouble.)
 *
 * '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.
 *
 * The result is the targetlist to be passed to the subplan.
 *---------------
 */
static List *
make_subplanTargetList(Query *parse,
                                           List *tlist,
                                           AttrNumber **groupColIdx)
{
        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 && !parse->havingQual)
                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);
        freeList(extravars);

        /*
         * 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 = length(parse->groupClause);
        if (numCols > 0)
        {
                int                     keyno = 0;
                AttrNumber *grpColIdx;
                List       *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;
                        List       *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(length(sub_tlist) + 1,
                                                                                                exprType(groupexpr),
                                                                                                exprTypmod(groupexpr),
                                                                                                NULL,
                                                                                                false),
                                                                         groupexpr);
                                sub_tlist = lappend(sub_tlist, te);
                        }

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

        return sub_tlist;
}

/*
 * make_groupplan
 *              Add a Group node for GROUP BY processing.
 *              If we couldn't make the subplan produce presorted output for grouping,
 *              first add an explicit Sort node.
 */
static Plan *
make_groupplan(List *group_tlist,
                           bool tuplePerGroup,
                           List *groupClause,
                           AttrNumber *grpColIdx,
                           bool is_presorted,
                           Plan *subplan)
{
        int                     numCols = length(groupClause);

        if (!is_presorted)
        {

                /*
                 * The Sort node always just takes a copy of the subplan's tlist
                 * plus ordering information.  (This might seem inefficient if the
                 * subplan contains complex GROUP BY expressions, but in fact Sort
                 * does not evaluate its targetlist --- it only outputs the same
                 * tuples in a new order.  So the expressions we might be copying
                 * are just dummies with no extra execution cost.)
                 */
                List       *sort_tlist = new_unsorted_tlist(subplan->targetlist);
                int                     keyno = 0;
                List       *gl;

                foreach(gl, groupClause)
                {
                        GroupClause *grpcl = (GroupClause *) lfirst(gl);
                        TargetEntry *te = nth(grpColIdx[keyno] - 1, sort_tlist);
                        Resdom     *resdom = te->resdom;

                        /*
                         * Check for the possibility of duplicate group-by clauses ---
                         * the parser should have removed 'em, but the Sort executor
                         * will get terribly confused if any get through!
                         */
                        if (resdom->reskey == 0)
                        {
                                /* OK, insert the ordering info needed by the executor. */
                                resdom->reskey = ++keyno;
                                resdom->reskeyop = get_opcode(grpcl->sortop);
                        }
                }

                Assert(keyno > 0);

                subplan = (Plan *) make_sort(sort_tlist, subplan, keyno);
        }

        return (Plan *) make_group(group_tlist, tuplePerGroup, numCols,
                                                           grpColIdx, subplan);
}

/*
 * make_sortplan
 *        Add a Sort node to implement an explicit ORDER BY clause.
 */
Plan *
make_sortplan(List *tlist, Plan *plannode, List *sortcls)
{
        List       *sort_tlist;
        List       *i;
        int                     keyno = 0;

        /*
         * First make a copy of the tlist so that we don't corrupt the
         * original.
         */
        sort_tlist = new_unsorted_tlist(tlist);

        foreach(i, sortcls)
        {
                SortClause *sortcl = (SortClause *) lfirst(i);
                TargetEntry *tle = get_sortgroupclause_tle(sortcl, sort_tlist);
                Resdom     *resdom = tle->resdom;

                /*
                 * Check for the possibility of duplicate order-by clauses --- the
                 * parser should have removed 'em, but the executor will get
                 * terribly confused if any get through!
                 */
                if (resdom->reskey == 0)
                {
                        /* OK, insert the ordering info needed by the executor. */
                        resdom->reskey = ++keyno;
                        resdom->reskeyop = get_opcode(sortcl->sortop);
                }
        }

        Assert(keyno > 0);

        return (Plan *) make_sort(sort_tlist, plannode, keyno);
}

/*
 * 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 elog if we
 * find any resjunk columns in orig_tlist.
 */
static List *
postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
{
        List       *l;

        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 != NIL);
                orig_tle = (TargetEntry *) lfirst(orig_tlist);
                orig_tlist = lnext(orig_tlist);
                if (orig_tle->resdom->resjunk)
                        elog(ERROR, "postprocess_setop_tlist: resjunk output columns 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 != NIL)
                elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented");
        return new_tlist;
}