granicus.if.org Git - postgresql/blob - src/backend/optimizer/plan/planner.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * planner.c
   4  *        The query optimizer external interface.
   5  *
   6  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.181 2005/03/28 00:58:23 tgl Exp $
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15
  16 #include "postgres.h"
  17
  18 #include <limits.h>
  19
  20 #include "catalog/pg_operator.h"
  21 #include "catalog/pg_type.h"
  22 #include "executor/executor.h"
  23 #include "executor/nodeAgg.h"
  24 #include "miscadmin.h"
  25 #include "nodes/makefuncs.h"
  26 #ifdef OPTIMIZER_DEBUG
  27 #include "nodes/print.h"
  28 #endif
  29 #include "optimizer/clauses.h"
  30 #include "optimizer/cost.h"
  31 #include "optimizer/pathnode.h"
  32 #include "optimizer/paths.h"
  33 #include "optimizer/planmain.h"
  34 #include "optimizer/planner.h"
  35 #include "optimizer/prep.h"
  36 #include "optimizer/subselect.h"
  37 #include "optimizer/tlist.h"
  38 #include "optimizer/var.h"
  39 #include "parser/parsetree.h"
  40 #include "parser/parse_expr.h"
  41 #include "parser/parse_oper.h"
  42 #include "utils/selfuncs.h"
  43 #include "utils/syscache.h"
  44
  45
  46 ParamListInfo PlannerBoundParamList = NULL;             /* current boundParams */
  47
  48
  49 /* Expression kind codes for preprocess_expression */
  50 #define EXPRKIND_QUAL   0
  51 #define EXPRKIND_TARGET 1
  52 #define EXPRKIND_RTFUNC 2
  53 #define EXPRKIND_LIMIT  3
  54 #define EXPRKIND_ININFO 4
  55
  56
  57 static Node *preprocess_expression(Query *parse, Node *expr, int kind);
  58 static void preprocess_qual_conditions(Query *parse, Node *jtnode);
  59 static Plan *inheritance_planner(Query *parse, List *inheritlist);
  60 static Plan *grouping_planner(Query *parse, double tuple_fraction);
  61 static bool hash_safe_grouping(Query *parse);
  62 static List *make_subplanTargetList(Query *parse, List *tlist,
  63                                            AttrNumber **groupColIdx, bool *need_tlist_eval);
  64 static void locate_grouping_columns(Query *parse,
  65                                                 List *tlist,
  66                                                 List *sub_tlist,
  67                                                 AttrNumber *groupColIdx);
  68 static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
  69
  70
  71 /*****************************************************************************
  72  *
  73  *         Query optimizer entry point
  74  *
  75  *****************************************************************************/
  76 Plan *
  77 planner(Query *parse, bool isCursor, int cursorOptions,
  78                 ParamListInfo boundParams)
  79 {
  80         double          tuple_fraction;
  81         Plan       *result_plan;
  82         Index           save_PlannerQueryLevel;
  83         List       *save_PlannerParamList;
  84         ParamListInfo save_PlannerBoundParamList;
  85
  86         /*
  87          * The planner can be called recursively (an example is when
  88          * eval_const_expressions tries to pre-evaluate an SQL function). So,
  89          * these global state variables must be saved and restored.
  90          *
  91          * Query level and the param list cannot be moved into the Query
  92          * structure since their whole purpose is communication across
  93          * multiple sub-Queries. Also, boundParams is explicitly info from
  94          * outside the Query, and so is likewise better handled as a global
  95          * variable.
  96          *
  97          * Note we do NOT save and restore PlannerPlanId: it exists to assign
  98          * unique IDs to SubPlan nodes, and we want those IDs to be unique for
  99          * the life of a backend.  Also, PlannerInitPlan is saved/restored in
 100          * subquery_planner, not here.
 101          */
 102         save_PlannerQueryLevel = PlannerQueryLevel;
 103         save_PlannerParamList = PlannerParamList;
 104         save_PlannerBoundParamList = PlannerBoundParamList;
 105
 106         /* Initialize state for handling outer-level references and params */
 107         PlannerQueryLevel = 0;          /* will be 1 in top-level subquery_planner */
 108         PlannerParamList = NIL;
 109         PlannerBoundParamList = boundParams;
 110
 111         /* Determine what fraction of the plan is likely to be scanned */
 112         if (isCursor)
 113         {
 114                 /*
 115                  * We have no real idea how many tuples the user will ultimately
 116                  * FETCH from a cursor, but it seems a good bet that he doesn't
 117                  * want 'em all.  Optimize for 10% retrieval (you gotta better
 118                  * number?      Should this be a SETtable parameter?)
 119                  */
 120                 tuple_fraction = 0.10;
 121         }
 122         else
 123         {
 124                 /* Default assumption is we need all the tuples */
 125                 tuple_fraction = 0.0;
 126         }
 127
 128         /* primary planning entry point (may recurse for subqueries) */
 129         result_plan = subquery_planner(parse, tuple_fraction);
 130
 131         Assert(PlannerQueryLevel == 0);
 132
 133         /*
 134          * If creating a plan for a scrollable cursor, make sure it can run
 135          * backwards on demand.  Add a Material node at the top at need.
 136          */
 137         if (isCursor && (cursorOptions & CURSOR_OPT_SCROLL))
 138         {
 139                 if (!ExecSupportsBackwardScan(result_plan))
 140                         result_plan = materialize_finished_plan(result_plan);
 141         }
 142
 143         /* executor wants to know total number of Params used overall */
 144         result_plan->nParamExec = list_length(PlannerParamList);
 145
 146         /* final cleanup of the plan */
 147         set_plan_references(result_plan, parse->rtable);
 148
 149         /* restore state for outer planner, if any */
 150         PlannerQueryLevel = save_PlannerQueryLevel;
 151         PlannerParamList = save_PlannerParamList;
 152         PlannerBoundParamList = save_PlannerBoundParamList;
 153
 154         return result_plan;
 155 }
 156
 157
 158 /*--------------------
 159  * subquery_planner
 160  *        Invokes the planner on a subquery.  We recurse to here for each
 161  *        sub-SELECT found in the query tree.
 162  *
 163  * parse is the querytree produced by the parser & rewriter.
 164  * tuple_fraction is the fraction of tuples we expect will be retrieved.
 165  * tuple_fraction is interpreted as explained for grouping_planner, below.
 166  *
 167  * Basically, this routine does the stuff that should only be done once
 168  * per Query object.  It then calls grouping_planner.  At one time,
 169  * grouping_planner could be invoked recursively on the same Query object;
 170  * that's not currently true, but we keep the separation between the two
 171  * routines anyway, in case we need it again someday.
 172  *
 173  * subquery_planner will be called recursively to handle sub-Query nodes
 174  * found within the query's expressions and rangetable.
 175  *
 176  * Returns a query plan.
 177  *--------------------
 178  */
 179 Plan *
 180 subquery_planner(Query *parse, double tuple_fraction)
 181 {
 182         List       *saved_initplan = PlannerInitPlan;
 183         int                     saved_planid = PlannerPlanId;
 184         bool            hasOuterJoins;
 185         Plan       *plan;
 186         List       *newHaving;
 187         List       *lst;
 188         ListCell   *l;
 189
 190         /* Set up for a new level of subquery */
 191         PlannerQueryLevel++;
 192         PlannerInitPlan = NIL;
 193
 194         /*
 195          * Look for IN clauses at the top level of WHERE, and transform them
 196          * into joins.  Note that this step only handles IN clauses originally
 197          * at top level of WHERE; if we pull up any subqueries in the next
 198          * step, their INs are processed just before pulling them up.
 199          */
 200         parse->in_info_list = NIL;
 201         if (parse->hasSubLinks)
 202                 parse->jointree->quals = pull_up_IN_clauses(parse,
 203                                                                                                  parse->jointree->quals);
 204
 205         /*
 206          * Check to see if any subqueries in the rangetable can be merged into
 207          * this query.
 208          */
 209         parse->jointree = (FromExpr *)
 210                 pull_up_subqueries(parse, (Node *) parse->jointree, false);
 211
 212         /*
 213          * Detect whether any rangetable entries are RTE_JOIN kind; if not, we
 214          * can avoid the expense of doing flatten_join_alias_vars().  Also
 215          * check for outer joins --- if none, we can skip
 216          * reduce_outer_joins(). This must be done after we have done
 217          * pull_up_subqueries, of course.
 218          */
 219         parse->hasJoinRTEs = false;
 220         hasOuterJoins = false;
 221         foreach(l, parse->rtable)
 222         {
 223                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 224
 225                 if (rte->rtekind == RTE_JOIN)
 226                 {
 227                         parse->hasJoinRTEs = true;
 228                         if (IS_OUTER_JOIN(rte->jointype))
 229                         {
 230                                 hasOuterJoins = true;
 231                                 /* Can quit scanning once we find an outer join */
 232                                 break;
 233                         }
 234                 }
 235         }
 236
 237         /*
 238          * Set hasHavingQual to remember if HAVING clause is present.  Needed
 239          * because preprocess_expression will reduce a constant-true condition
 240          * to an empty qual list ... but "HAVING TRUE" is not a semantic no-op.
 241          */
 242         parse->hasHavingQual = (parse->havingQual != NULL);
 243
 244         /*
 245          * Do expression preprocessing on targetlist and quals.
 246          */
 247         parse->targetList = (List *)
 248                 preprocess_expression(parse, (Node *) parse->targetList,
 249                                                           EXPRKIND_TARGET);
 250
 251         preprocess_qual_conditions(parse, (Node *) parse->jointree);
 252
 253         parse->havingQual = preprocess_expression(parse, parse->havingQual,
 254                                                                                           EXPRKIND_QUAL);
 255
 256         parse->limitOffset = preprocess_expression(parse, parse->limitOffset,
 257                                                                                            EXPRKIND_LIMIT);
 258         parse->limitCount = preprocess_expression(parse, parse->limitCount,
 259                                                                                           EXPRKIND_LIMIT);
 260
 261         parse->in_info_list = (List *)
 262                 preprocess_expression(parse, (Node *) parse->in_info_list,
 263                                                           EXPRKIND_ININFO);
 264
 265         /* Also need to preprocess expressions for function RTEs */
 266         foreach(l, parse->rtable)
 267         {
 268                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 269
 270                 if (rte->rtekind == RTE_FUNCTION)
 271                         rte->funcexpr = preprocess_expression(parse, rte->funcexpr,
 272                                                                                                   EXPRKIND_RTFUNC);
 273         }
 274
 275         /*
 276          * In some cases we may want to transfer a HAVING clause into WHERE.
 277          * We cannot do so if the HAVING clause contains aggregates (obviously)
 278          * or volatile functions (since a HAVING clause is supposed to be executed
 279          * only once per group).  Also, it may be that the clause is so expensive
 280          * to execute that we're better off doing it only once per group, despite
 281          * the loss of selectivity.  This is hard to estimate short of doing the
 282          * entire planning process twice, so we use a heuristic: clauses
 283          * containing subplans are left in HAVING.  Otherwise, we move or copy
 284          * the HAVING clause into WHERE, in hopes of eliminating tuples before
 285          * aggregation instead of after.
 286          *
 287          * If the query has explicit grouping then we can simply move such a
 288          * clause into WHERE; any group that fails the clause will not be
 289          * in the output because none of its tuples will reach the grouping
 290          * or aggregation stage.  Otherwise we must have a degenerate
 291          * (variable-free) HAVING clause, which we put in WHERE so that
 292          * query_planner() can use it in a gating Result node, but also keep
 293          * in HAVING to ensure that we don't emit a bogus aggregated row.
 294          * (This could be done better, but it seems not worth optimizing.)
 295          *
 296          * Note that both havingQual and parse->jointree->quals are in
 297          * implicitly-ANDed-list form at this point, even though they are
 298          * declared as Node *.
 299          */
 300         newHaving = NIL;
 301         foreach(l, (List *) parse->havingQual)
 302         {
 303                 Node       *havingclause = (Node *) lfirst(l);
 304
 305                 if (contain_agg_clause(havingclause) ||
 306                         contain_volatile_functions(havingclause) ||
 307                         contain_subplans(havingclause))
 308                 {
 309                         /* keep it in HAVING */
 310                         newHaving = lappend(newHaving, havingclause);
 311                 }
 312                 else if (parse->groupClause)
 313                 {
 314                         /* move it to WHERE */
 315                         parse->jointree->quals = (Node *)
 316                                 lappend((List *) parse->jointree->quals, havingclause);
 317                 }
 318                 else
 319                 {
 320                         /* put a copy in WHERE, keep it in HAVING */
 321                         parse->jointree->quals = (Node *)
 322                                 lappend((List *) parse->jointree->quals,
 323                                                 copyObject(havingclause));
 324                         newHaving = lappend(newHaving, havingclause);
 325                 }
 326         }
 327         parse->havingQual = (Node *) newHaving;
 328
 329         /*
 330          * If we have any outer joins, try to reduce them to plain inner
 331          * joins. This step is most easily done after we've done expression
 332          * preprocessing.
 333          */
 334         if (hasOuterJoins)
 335                 reduce_outer_joins(parse);
 336
 337         /*
 338          * See if we can simplify the jointree; opportunities for this may
 339          * come from having pulled up subqueries, or from flattening explicit
 340          * JOIN syntax.  We must do this after flattening JOIN alias
 341          * variables, since eliminating explicit JOIN nodes from the jointree
 342          * will cause get_relids_for_join() to fail.  But it should happen
 343          * after reduce_outer_joins, anyway.
 344          */
 345         parse->jointree = (FromExpr *)
 346                 simplify_jointree(parse, (Node *) parse->jointree);
 347
 348         /*
 349          * Do the main planning.  If we have an inherited target relation,
 350          * that needs special processing, else go straight to
 351          * grouping_planner.
 352          */
 353         if (parse->resultRelation &&
 354                 (lst = expand_inherited_rtentry(parse, parse->resultRelation)) != NIL)
 355                 plan = inheritance_planner(parse, lst);
 356         else
 357                 plan = grouping_planner(parse, tuple_fraction);
 358
 359         /*
 360          * If any subplans were generated, or if we're inside a subplan, build
 361          * initPlan list and extParam/allParam sets for plan nodes.
 362          */
 363         if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1)
 364         {
 365                 Cost            initplan_cost = 0;
 366
 367                 /* Prepare extParam/allParam sets for all nodes in tree */
 368                 SS_finalize_plan(plan, parse->rtable);
 369
 370                 /*
 371                  * SS_finalize_plan doesn't handle initPlans, so we have to
 372                  * manually attach them to the topmost plan node, and add their
 373                  * extParams to the topmost node's, too.
 374                  *
 375                  * We also add the total_cost of each initPlan to the startup cost of
 376                  * the top node.  This is a conservative overestimate, since in
 377                  * fact each initPlan might be executed later than plan startup,
 378                  * or even not at all.
 379                  */
 380                 plan->initPlan = PlannerInitPlan;
 381
 382                 foreach(l, plan->initPlan)
 383                 {
 384                         SubPlan    *initplan = (SubPlan *) lfirst(l);
 385
 386                         plan->extParam = bms_add_members(plan->extParam,
 387                                                                                          initplan->plan->extParam);
 388                         /* allParam must include all members of extParam */
 389                         plan->allParam = bms_add_members(plan->allParam,
 390                                                                                          plan->extParam);
 391                         initplan_cost += initplan->plan->total_cost;
 392                 }
 393
 394                 plan->startup_cost += initplan_cost;
 395                 plan->total_cost += initplan_cost;
 396         }
 397
 398         /* Return to outer subquery context */
 399         PlannerQueryLevel--;
 400         PlannerInitPlan = saved_initplan;
 401         /* we do NOT restore PlannerPlanId; that's not an oversight! */
 402
 403         return plan;
 404 }
 405
 406 /*
 407  * preprocess_expression
 408  *              Do subquery_planner's preprocessing work for an expression,
 409  *              which can be a targetlist, a WHERE clause (including JOIN/ON
 410  *              conditions), or a HAVING clause.
 411  */
 412 static Node *
 413 preprocess_expression(Query *parse, Node *expr, int kind)
 414 {
 415         /*
 416          * If the query has any join RTEs, replace join alias variables with
 417          * base-relation variables. We must do this before sublink processing,
 418          * else sublinks expanded out from join aliases wouldn't get
 419          * processed.
 420          */
 421         if (parse->hasJoinRTEs)
 422                 expr = flatten_join_alias_vars(parse, expr);
 423
 424         /*
 425          * Simplify constant expressions.
 426          *
 427          * Note: this also flattens nested AND and OR expressions into N-argument
 428          * form.  All processing of a qual expression after this point must be
 429          * careful to maintain AND/OR flatness --- that is, do not generate a tree
 430          * with AND directly under AND, nor OR directly under OR.
 431          */
 432         expr = eval_const_expressions(expr);
 433
 434         /*
 435          * If it's a qual or havingQual, canonicalize it.
 436          */
 437         if (kind == EXPRKIND_QUAL)
 438         {
 439                 expr = (Node *) canonicalize_qual((Expr *) expr);
 440
 441 #ifdef OPTIMIZER_DEBUG
 442                 printf("After canonicalize_qual()\n");
 443                 pprint(expr);
 444 #endif
 445         }
 446
 447         /* Expand SubLinks to SubPlans */
 448         if (parse->hasSubLinks)
 449                 expr = SS_process_sublinks(expr, (kind == EXPRKIND_QUAL));
 450
 451         /*
 452          * XXX do not insert anything here unless you have grokked the
 453          * comments in SS_replace_correlation_vars ...
 454          */
 455
 456         /* Replace uplevel vars with Param nodes */
 457         if (PlannerQueryLevel > 1)
 458                 expr = SS_replace_correlation_vars(expr);
 459
 460         /*
 461          * If it's a qual or havingQual, convert it to implicit-AND format.
 462          * (We don't want to do this before eval_const_expressions, since the
 463          * latter would be unable to simplify a top-level AND correctly. Also,
 464          * SS_process_sublinks expects explicit-AND format.)
 465          */
 466         if (kind == EXPRKIND_QUAL)
 467                 expr = (Node *) make_ands_implicit((Expr *) expr);
 468
 469         return expr;
 470 }
 471
 472 /*
 473  * preprocess_qual_conditions
 474  *              Recursively scan the query's jointree and do subquery_planner's
 475  *              preprocessing work on each qual condition found therein.
 476  */
 477 static void
 478 preprocess_qual_conditions(Query *parse, Node *jtnode)
 479 {
 480         if (jtnode == NULL)
 481                 return;
 482         if (IsA(jtnode, RangeTblRef))
 483         {
 484                 /* nothing to do here */
 485         }
 486         else if (IsA(jtnode, FromExpr))
 487         {
 488                 FromExpr   *f = (FromExpr *) jtnode;
 489                 ListCell   *l;
 490
 491                 foreach(l, f->fromlist)
 492                         preprocess_qual_conditions(parse, lfirst(l));
 493
 494                 f->quals = preprocess_expression(parse, f->quals, EXPRKIND_QUAL);
 495         }
 496         else if (IsA(jtnode, JoinExpr))
 497         {
 498                 JoinExpr   *j = (JoinExpr *) jtnode;
 499
 500                 preprocess_qual_conditions(parse, j->larg);
 501                 preprocess_qual_conditions(parse, j->rarg);
 502
 503                 j->quals = preprocess_expression(parse, j->quals, EXPRKIND_QUAL);
 504         }
 505         else
 506                 elog(ERROR, "unrecognized node type: %d",
 507                          (int) nodeTag(jtnode));
 508 }
 509
 510 /*--------------------
 511  * inheritance_planner
 512  *        Generate a plan in the case where the result relation is an
 513  *        inheritance set.
 514  *
 515  * We have to handle this case differently from cases where a source
 516  * relation is an inheritance set.      Source inheritance is expanded at
 517  * the bottom of the plan tree (see allpaths.c), but target inheritance
 518  * has to be expanded at the top.  The reason is that for UPDATE, each
 519  * target relation needs a different targetlist matching its own column
 520  * set.  (This is not so critical for DELETE, but for simplicity we treat
 521  * inherited DELETE the same way.)      Fortunately, the UPDATE/DELETE target
 522  * can never be the nullable side of an outer join, so it's OK to generate
 523  * the plan this way.
 524  *
 525  * parse is the querytree produced by the parser & rewriter.
 526  * inheritlist is an integer list of RT indexes for the result relation set.
 527  *
 528  * Returns a query plan.
 529  *--------------------
 530  */
 531 static Plan *
 532 inheritance_planner(Query *parse, List *inheritlist)
 533 {
 534         int                     parentRTindex = parse->resultRelation;
 535         Oid                     parentOID = getrelid(parentRTindex, parse->rtable);
 536         int                     mainrtlength = list_length(parse->rtable);
 537         List       *subplans = NIL;
 538         List       *tlist = NIL;
 539         ListCell   *l;
 540
 541         foreach(l, inheritlist)
 542         {
 543                 int                     childRTindex = lfirst_int(l);
 544                 Oid                     childOID = getrelid(childRTindex, parse->rtable);
 545                 Query      *subquery;
 546                 Plan       *subplan;
 547
 548                 /* Generate modified query with this rel as target */
 549                 subquery = (Query *) adjust_inherited_attrs((Node *) parse,
 550                                                                                                 parentRTindex, parentOID,
 551                                                                                                  childRTindex, childOID);
 552                 /* Generate plan */
 553                 subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */ );
 554                 subplans = lappend(subplans, subplan);
 555
 556                 /*
 557                  * XXX my goodness this next bit is ugly.  Really need to think about
 558                  * ways to rein in planner's habit of scribbling on its input.
 559                  *
 560                  * Planning of the subquery might have modified the rangetable,
 561                  * either by addition of RTEs due to expansion of inherited source
 562                  * tables, or by changes of the Query structures inside subquery
 563                  * RTEs.  We have to ensure that this gets propagated back to the
 564                  * master copy.  However, if we aren't done planning yet, we also
 565                  * need to ensure that subsequent calls to grouping_planner have
 566                  * virgin sub-Queries to work from.  So, if we are at the last
 567                  * list entry, just copy the subquery rangetable back to the master
 568                  * copy; if we are not, then extend the master copy by adding
 569                  * whatever the subquery added.  (We assume these added entries
 570                  * will go untouched by the future grouping_planner calls.  We are
 571                  * also effectively assuming that sub-Queries will get planned
 572                  * identically each time, or at least that the impacts on their
 573                  * rangetables will be the same each time.  Did I say this is ugly?)
 574                  */
 575                 if (lnext(l) == NULL)
 576                         parse->rtable = subquery->rtable;
 577                 else
 578                 {
 579                         int             subrtlength = list_length(subquery->rtable);
 580
 581                         if (subrtlength > mainrtlength)
 582                         {
 583                                 List       *subrt;
 584
 585                                 subrt = list_copy_tail(subquery->rtable, mainrtlength);
 586                                 parse->rtable = list_concat(parse->rtable, subrt);
 587                                 mainrtlength = subrtlength;
 588                         }
 589                 }
 590
 591                 /* Save preprocessed tlist from first rel for use in Append */
 592                 if (tlist == NIL)
 593                         tlist = subplan->targetlist;
 594         }
 595
 596         /* Save the target-relations list for the executor, too */
 597         parse->resultRelations = inheritlist;
 598
 599         /* Mark result as unordered (probably unnecessary) */
 600         parse->query_pathkeys = NIL;
 601
 602         return (Plan *) make_append(subplans, true, tlist);
 603 }
 604
 605 /*--------------------
 606  * grouping_planner
 607  *        Perform planning steps related to grouping, aggregation, etc.
 608  *        This primarily means adding top-level processing to the basic
 609  *        query plan produced by query_planner.
 610  *
 611  * parse is the querytree produced by the parser & rewriter.
 612  * tuple_fraction is the fraction of tuples we expect will be retrieved
 613  *
 614  * tuple_fraction is interpreted as follows:
 615  *        0: expect all tuples to be retrieved (normal case)
 616  *        0 < tuple_fraction < 1: expect the given fraction of tuples available
 617  *              from the plan to be retrieved
 618  *        tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 619  *              expected to be retrieved (ie, a LIMIT specification)
 620  *
 621  * Returns a query plan.  Also, parse->query_pathkeys is returned as the
 622  * actual output ordering of the plan (in pathkey format).
 623  *--------------------
 624  */
 625 static Plan *
 626 grouping_planner(Query *parse, double tuple_fraction)
 627 {
 628         List       *tlist = parse->targetList;
 629         Plan       *result_plan;
 630         List       *current_pathkeys;
 631         List       *sort_pathkeys;
 632
 633         if (parse->setOperations)
 634         {
 635                 List       *set_sortclauses;
 636
 637                 /*
 638                  * Construct the plan for set operations.  The result will not
 639                  * need any work except perhaps a top-level sort and/or LIMIT.
 640                  */
 641                 result_plan = plan_set_operations(parse,
 642                                                                                   &set_sortclauses);
 643
 644                 /*
 645                  * Calculate pathkeys representing the sort order (if any) of the
 646                  * set operation's result.  We have to do this before overwriting
 647                  * the sort key information...
 648                  */
 649                 current_pathkeys = make_pathkeys_for_sortclauses(set_sortclauses,
 650                                                                                                 result_plan->targetlist);
 651                 current_pathkeys = canonicalize_pathkeys(parse, current_pathkeys);
 652
 653                 /*
 654                  * We should not need to call preprocess_targetlist, since we must
 655                  * be in a SELECT query node.  Instead, use the targetlist
 656                  * returned by plan_set_operations (since this tells whether it
 657                  * returned any resjunk columns!), and transfer any sort key
 658                  * information from the original tlist.
 659                  */
 660                 Assert(parse->commandType == CMD_SELECT);
 661
 662                 tlist = postprocess_setop_tlist(result_plan->targetlist, tlist);
 663
 664                 /*
 665                  * Can't handle FOR UPDATE here (parser should have checked
 666                  * already, but let's make sure).
 667                  */
 668                 if (parse->rowMarks)
 669                         ereport(ERROR,
 670                                         (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 671                                          errmsg("SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT")));
 672
 673                 /*
 674                  * Calculate pathkeys that represent result ordering requirements
 675                  */
 676                 sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
 677                                                                                                           tlist);
 678                 sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
 679         }
 680         else
 681         {
 682                 /* No set operations, do regular planning */
 683                 List       *sub_tlist;
 684                 List       *group_pathkeys;
 685                 AttrNumber *groupColIdx = NULL;
 686                 bool            need_tlist_eval = true;
 687                 QualCost        tlist_cost;
 688                 double          sub_tuple_fraction;
 689                 Path       *cheapest_path;
 690                 Path       *sorted_path;
 691                 double          dNumGroups = 0;
 692                 long            numGroups = 0;
 693                 AggClauseCounts agg_counts;
 694                 int                     numGroupCols = list_length(parse->groupClause);
 695                 bool            use_hashed_grouping = false;
 696
 697                 MemSet(&agg_counts, 0, sizeof(AggClauseCounts));
 698
 699                 /* Preprocess targetlist */
 700                 tlist = preprocess_targetlist(parse, tlist);
 701
 702                 /*
 703                  * Generate appropriate target list for subplan; may be different
 704                  * from tlist if grouping or aggregation is needed.
 705                  */
 706                 sub_tlist = make_subplanTargetList(parse, tlist,
 707                                                                                  &groupColIdx, &need_tlist_eval);
 708
 709                 /*
 710                  * Calculate pathkeys that represent grouping/ordering
 711                  * requirements
 712                  */
 713                 group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause,
 714                                                                                                            tlist);
 715                 sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause,
 716                                                                                                           tlist);
 717
 718                 /*
 719                  * Will need actual number of aggregates for estimating costs.
 720                  *
 721                  * Note: we do not attempt to detect duplicate aggregates here; a
 722                  * somewhat-overestimated count is okay for our present purposes.
 723                  *
 724                  * Note: think not that we can turn off hasAggs if we find no aggs.
 725                  * It is possible for constant-expression simplification to remove
 726                  * all explicit references to aggs, but we still have to follow
 727                  * the aggregate semantics (eg, producing only one output row).
 728                  */
 729                 if (parse->hasAggs)
 730                 {
 731                         count_agg_clauses((Node *) tlist, &agg_counts);
 732                         count_agg_clauses(parse->havingQual, &agg_counts);
 733                 }
 734
 735                 /*
 736                  * Figure out whether we need a sorted result from query_planner.
 737                  *
 738                  * If we have a GROUP BY clause, then we want a result sorted
 739                  * properly for grouping.  Otherwise, if there is an ORDER BY
 740                  * clause, we want to sort by the ORDER BY clause.      (Note: if we
 741                  * have both, and ORDER BY is a superset of GROUP BY, it would be
 742                  * tempting to request sort by ORDER BY --- but that might just
 743                  * leave us failing to exploit an available sort order at all.
 744                  * Needs more thought...)
 745                  */
 746                 if (parse->groupClause)
 747                         parse->query_pathkeys = group_pathkeys;
 748                 else if (parse->sortClause)
 749                         parse->query_pathkeys = sort_pathkeys;
 750                 else
 751                         parse->query_pathkeys = NIL;
 752
 753                 /*
 754                  * Adjust tuple_fraction if we see that we are going to apply
 755                  * limiting/grouping/aggregation/etc.  This is not overridable by
 756                  * the caller, since it reflects plan actions that this routine
 757                  * will certainly take, not assumptions about context.
 758                  */
 759                 if (parse->limitCount != NULL)
 760                 {
 761                         /*
 762                          * A LIMIT clause limits the absolute number of tuples
 763                          * returned. However, if it's not a constant LIMIT then we
 764                          * have to punt; for lack of a better idea, assume 10% of the
 765                          * plan's result is wanted.
 766                          */
 767                         double          limit_fraction = 0.0;
 768
 769                         if (IsA(parse->limitCount, Const))
 770                         {
 771                                 Const      *limitc = (Const *) parse->limitCount;
 772                                 int32           count = DatumGetInt32(limitc->constvalue);
 773
 774                                 /*
 775                                  * A NULL-constant LIMIT represents "LIMIT ALL", which we
 776                                  * treat the same as no limit (ie, expect to retrieve all
 777                                  * the tuples).
 778                                  */
 779                                 if (!limitc->constisnull && count > 0)
 780                                 {
 781                                         limit_fraction = (double) count;
 782                                         /* We must also consider the OFFSET, if present */
 783                                         if (parse->limitOffset != NULL)
 784                                         {
 785                                                 if (IsA(parse->limitOffset, Const))
 786                                                 {
 787                                                         int32           offset;
 788
 789                                                         limitc = (Const *) parse->limitOffset;
 790                                                         offset = DatumGetInt32(limitc->constvalue);
 791                                                         if (!limitc->constisnull && offset > 0)
 792                                                                 limit_fraction += (double) offset;
 793                                                 }
 794                                                 else
 795                                                 {
 796                                                         /* OFFSET is an expression ... punt ... */
 797                                                         limit_fraction = 0.10;
 798                                                 }
 799                                         }
 800                                 }
 801                         }
 802                         else
 803                         {
 804                                 /* LIMIT is an expression ... punt ... */
 805                                 limit_fraction = 0.10;
 806                         }
 807
 808                         if (limit_fraction > 0.0)
 809                         {
 810                                 /*
 811                                  * If we have absolute limits from both caller and LIMIT,
 812                                  * use the smaller value; if one is fractional and the
 813                                  * other absolute, treat the fraction as a fraction of the
 814                                  * absolute value; else we can multiply the two fractions
 815                                  * together.
 816                                  */
 817                                 if (tuple_fraction >= 1.0)
 818                                 {
 819                                         if (limit_fraction >= 1.0)
 820                                         {
 821                                                 /* both absolute */
 822                                                 tuple_fraction = Min(tuple_fraction, limit_fraction);
 823                                         }
 824                                         else
 825                                         {
 826                                                 /* caller absolute, limit fractional */
 827                                                 tuple_fraction *= limit_fraction;
 828                                                 if (tuple_fraction < 1.0)
 829                                                         tuple_fraction = 1.0;
 830                                         }
 831                                 }
 832                                 else if (tuple_fraction > 0.0)
 833                                 {
 834                                         if (limit_fraction >= 1.0)
 835                                         {
 836                                                 /* caller fractional, limit absolute */
 837                                                 tuple_fraction *= limit_fraction;
 838                                                 if (tuple_fraction < 1.0)
 839                                                         tuple_fraction = 1.0;
 840                                         }
 841                                         else
 842                                         {
 843                                                 /* both fractional */
 844                                                 tuple_fraction *= limit_fraction;
 845                                         }
 846                                 }
 847                                 else
 848                                 {
 849                                         /* no info from caller, just use limit */
 850                                         tuple_fraction = limit_fraction;
 851                                 }
 852                         }
 853                 }
 854
 855                 /*
 856                  * With grouping or aggregation, the tuple fraction to pass to
 857                  * query_planner() may be different from what it is at top level.
 858                  */
 859                 sub_tuple_fraction = tuple_fraction;
 860
 861                 if (parse->groupClause)
 862                 {
 863                         /*
 864                          * In GROUP BY mode, we have the little problem that we don't
 865                          * really know how many input tuples will be needed to make a
 866                          * group, so we can't translate an output LIMIT count into an
 867                          * input count.  For lack of a better idea, assume 25% of the
 868                          * input data will be processed if there is any output limit.
 869                          * However, if the caller gave us a fraction rather than an
 870                          * absolute count, we can keep using that fraction (which
 871                          * amounts to assuming that all the groups are about the same
 872                          * size).
 873                          */
 874                         if (sub_tuple_fraction >= 1.0)
 875                                 sub_tuple_fraction = 0.25;
 876
 877                         /*
 878                          * If both GROUP BY and ORDER BY are specified, we will need
 879                          * two levels of sort --- and, therefore, certainly need to
 880                          * read all the input tuples --- unless ORDER BY is a subset
 881                          * of GROUP BY.  (We have not yet canonicalized the pathkeys,
 882                          * so must use the slower noncanonical comparison method.)
 883                          */
 884                         if (parse->groupClause && parse->sortClause &&
 885                                 !noncanonical_pathkeys_contained_in(sort_pathkeys,
 886                                                                                                         group_pathkeys))
 887                                 sub_tuple_fraction = 0.0;
 888                 }
 889                 else if (parse->hasAggs)
 890                 {
 891                         /*
 892                          * Ungrouped aggregate will certainly want all the input
 893                          * tuples.
 894                          */
 895                         sub_tuple_fraction = 0.0;
 896                 }
 897                 else if (parse->distinctClause)
 898                 {
 899                         /*
 900                          * SELECT DISTINCT, like GROUP, will absorb an unpredictable
 901                          * number of input tuples per output tuple.  Handle the same
 902                          * way.
 903                          */
 904                         if (sub_tuple_fraction >= 1.0)
 905                                 sub_tuple_fraction = 0.25;
 906                 }
 907
 908                 /*
 909                  * Generate the best unsorted and presorted paths for this Query
 910                  * (but note there may not be any presorted path).
 911                  */
 912                 query_planner(parse, sub_tlist, sub_tuple_fraction,
 913                                           &cheapest_path, &sorted_path);
 914
 915                 /*
 916                  * We couldn't canonicalize group_pathkeys and sort_pathkeys
 917                  * before running query_planner(), so do it now.
 918                  */
 919                 group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys);
 920                 sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys);
 921
 922                 /*
 923                  * Consider whether we might want to use hashed grouping.
 924                  */
 925                 if (parse->groupClause)
 926                 {
 927                         List       *groupExprs;
 928                         double          cheapest_path_rows;
 929                         int                     cheapest_path_width;
 930
 931                         /*
 932                          * Beware in this section of the possibility that
 933                          * cheapest_path->parent is NULL.  This could happen if user
 934                          * does something silly like SELECT 'foo' GROUP BY 1;
 935                          */
 936                         if (cheapest_path->parent)
 937                         {
 938                                 cheapest_path_rows = cheapest_path->parent->rows;
 939                                 cheapest_path_width = cheapest_path->parent->width;
 940                         }
 941                         else
 942                         {
 943                                 cheapest_path_rows = 1; /* assume non-set result */
 944                                 cheapest_path_width = 100;              /* arbitrary */
 945                         }
 946
 947                         /*
 948                          * Always estimate the number of groups.  We can't do this
 949                          * until after running query_planner(), either.
 950                          */
 951                         groupExprs = get_sortgrouplist_exprs(parse->groupClause,
 952                                                                                                  parse->targetList);
 953                         dNumGroups = estimate_num_groups(parse,
 954                                                                                          groupExprs,
 955                                                                                          cheapest_path_rows);
 956                         /* Also want it as a long int --- but 'ware overflow! */
 957                         numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 958
 959                         /*
 960                          * Check can't-do-it conditions, including whether the
 961                          * grouping operators are hashjoinable.
 962                          *
 963                          * Executor doesn't support hashed aggregation with DISTINCT
 964                          * aggregates.  (Doing so would imply storing *all* the input
 965                          * values in the hash table, which seems like a certain
 966                          * loser.)
 967                          */
 968                         if (!enable_hashagg || !hash_safe_grouping(parse))
 969                                 use_hashed_grouping = false;
 970                         else if (agg_counts.numDistinctAggs != 0)
 971                                 use_hashed_grouping = false;
 972                         else
 973                         {
 974                                 /*
 975                                  * Use hashed grouping if (a) we think we can fit the
 976                                  * hashtable into work_mem, *and* (b) the estimated cost
 977                                  * is no more than doing it the other way.      While avoiding
 978                                  * the need for sorted input is usually a win, the fact
 979                                  * that the output won't be sorted may be a loss; so we
 980                                  * need to do an actual cost comparison.
 981                                  */
 982                                 Size            hashentrysize;
 983
 984                                 /* Estimate per-hash-entry space at tuple width... */
 985                                 hashentrysize = cheapest_path_width;
 986                                 /* plus space for pass-by-ref transition values... */
 987                                 hashentrysize += agg_counts.transitionSpace;
 988                                 /* plus the per-hash-entry overhead */
 989                                 hashentrysize += hash_agg_entry_size(agg_counts.numAggs);
 990
 991                                 if (hashentrysize * dNumGroups <= work_mem * 1024L)
 992                                 {
 993                                         /*
 994                                          * Okay, do the cost comparison.  We need to consider
 995                                          * cheapest_path + hashagg [+ final sort] versus
 996                                          * either cheapest_path [+ sort] + group or agg [+
 997                                          * final sort] or presorted_path + group or agg [+
 998                                          * final sort] where brackets indicate a step that may
 999                                          * not be needed. We assume query_planner() will have
1000                                          * returned a presorted path only if it's a winner
1001                                          * compared to cheapest_path for this purpose.
1002                                          *
1003                                          * These path variables are dummies that just hold cost
1004                                          * fields; we don't make actual Paths for these steps.
1005                                          */
1006                                         Path            hashed_p;
1007                                         Path            sorted_p;
1008
1009                                         cost_agg(&hashed_p, parse,
1010                                                          AGG_HASHED, agg_counts.numAggs,
1011                                                          numGroupCols, dNumGroups,
1012                                                          cheapest_path->startup_cost,
1013                                                          cheapest_path->total_cost,
1014                                                          cheapest_path_rows);
1015                                         /* Result of hashed agg is always unsorted */
1016                                         if (sort_pathkeys)
1017                                                 cost_sort(&hashed_p, parse, sort_pathkeys,
1018                                                                   hashed_p.total_cost,
1019                                                                   dNumGroups,
1020                                                                   cheapest_path_width);
1021
1022                                         if (sorted_path)
1023                                         {
1024                                                 sorted_p.startup_cost = sorted_path->startup_cost;
1025                                                 sorted_p.total_cost = sorted_path->total_cost;
1026                                                 current_pathkeys = sorted_path->pathkeys;
1027                                         }
1028                                         else
1029                                         {
1030                                                 sorted_p.startup_cost = cheapest_path->startup_cost;
1031                                                 sorted_p.total_cost = cheapest_path->total_cost;
1032                                                 current_pathkeys = cheapest_path->pathkeys;
1033                                         }
1034                                         if (!pathkeys_contained_in(group_pathkeys,
1035                                                                                            current_pathkeys))
1036                                         {
1037                                                 cost_sort(&sorted_p, parse, group_pathkeys,
1038                                                                   sorted_p.total_cost,
1039                                                                   cheapest_path_rows,
1040                                                                   cheapest_path_width);
1041                                                 current_pathkeys = group_pathkeys;
1042                                         }
1043                                         if (parse->hasAggs)
1044                                                 cost_agg(&sorted_p, parse,
1045                                                                  AGG_SORTED, agg_counts.numAggs,
1046                                                                  numGroupCols, dNumGroups,
1047                                                                  sorted_p.startup_cost,
1048                                                                  sorted_p.total_cost,
1049                                                                  cheapest_path_rows);
1050                                         else
1051                                                 cost_group(&sorted_p, parse,
1052                                                                    numGroupCols, dNumGroups,
1053                                                                    sorted_p.startup_cost,
1054                                                                    sorted_p.total_cost,
1055                                                                    cheapest_path_rows);
1056                                         /* The Agg or Group node will preserve ordering */
1057                                         if (sort_pathkeys &&
1058                                                 !pathkeys_contained_in(sort_pathkeys,
1059                                                                                            current_pathkeys))
1060                                         {
1061                                                 cost_sort(&sorted_p, parse, sort_pathkeys,
1062                                                                   sorted_p.total_cost,
1063                                                                   dNumGroups,
1064                                                                   cheapest_path_width);
1065                                         }
1066
1067                                         /*
1068                                          * Now make the decision using the top-level tuple
1069                                          * fraction.  First we have to convert an absolute
1070                                          * count (LIMIT) into fractional form.
1071                                          */
1072                                         if (tuple_fraction >= 1.0)
1073                                                 tuple_fraction /= dNumGroups;
1074
1075                                         if (compare_fractional_path_costs(&hashed_p, &sorted_p,
1076                                                                                                           tuple_fraction) < 0)
1077                                         {
1078                                                 /* Hashed is cheaper, so use it */
1079                                                 use_hashed_grouping = true;
1080                                         }
1081                                 }
1082                         }
1083                 }
1084
1085                 /*
1086                  * Select the best path and create a plan to execute it.
1087                  *
1088                  * If we are doing hashed grouping, we will always read all the input
1089                  * tuples, so use the cheapest-total path.      Otherwise, trust
1090                  * query_planner's decision about which to use.
1091                  */
1092                 if (sorted_path && !use_hashed_grouping)
1093                 {
1094                         result_plan = create_plan(parse, sorted_path);
1095                         current_pathkeys = sorted_path->pathkeys;
1096                 }
1097                 else
1098                 {
1099                         result_plan = create_plan(parse, cheapest_path);
1100                         current_pathkeys = cheapest_path->pathkeys;
1101                 }
1102
1103                 /*
1104                  * create_plan() returns a plan with just a "flat" tlist of
1105                  * required Vars.  Usually we need to insert the sub_tlist as the
1106                  * tlist of the top plan node.  However, we can skip that if we
1107                  * determined that whatever query_planner chose to return will be
1108                  * good enough.
1109                  */
1110                 if (need_tlist_eval)
1111                 {
1112                         /*
1113                          * If the top-level plan node is one that cannot do expression
1114                          * evaluation, we must insert a Result node to project the
1115                          * desired tlist.
1116                          */
1117                         if (!is_projection_capable_plan(result_plan))
1118                         {
1119                                 result_plan = (Plan *) make_result(sub_tlist, NULL,
1120                                                                                                    result_plan);
1121                         }
1122                         else
1123                         {
1124                                 /*
1125                                  * Otherwise, just replace the subplan's flat tlist with
1126                                  * the desired tlist.
1127                                  */
1128                                 result_plan->targetlist = sub_tlist;
1129                         }
1130
1131                         /*
1132                          * Also, account for the cost of evaluation of the sub_tlist.
1133                          *
1134                          * Up to now, we have only been dealing with "flat" tlists,
1135                          * containing just Vars.  So their evaluation cost is zero
1136                          * according to the model used by cost_qual_eval() (or if you
1137                          * prefer, the cost is factored into cpu_tuple_cost).  Thus we
1138                          * can avoid accounting for tlist cost throughout
1139                          * query_planner() and subroutines.  But now we've inserted a
1140                          * tlist that might contain actual operators, sub-selects, etc
1141                          * --- so we'd better account for its cost.
1142                          *
1143                          * Below this point, any tlist eval cost for added-on nodes
1144                          * should be accounted for as we create those nodes.
1145                          * Presently, of the node types we can add on, only Agg and
1146                          * Group project new tlists (the rest just copy their input
1147                          * tuples) --- so make_agg() and make_group() are responsible
1148                          * for computing the added cost.
1149                          */
1150                         cost_qual_eval(&tlist_cost, sub_tlist);
1151                         result_plan->startup_cost += tlist_cost.startup;
1152                         result_plan->total_cost += tlist_cost.startup +
1153                                 tlist_cost.per_tuple * result_plan->plan_rows;
1154                 }
1155                 else
1156                 {
1157                         /*
1158                          * Since we're using query_planner's tlist and not the one
1159                          * make_subplanTargetList calculated, we have to refigure any
1160                          * grouping-column indexes make_subplanTargetList computed.
1161                          */
1162                         locate_grouping_columns(parse, tlist, result_plan->targetlist,
1163                                                                         groupColIdx);
1164                 }
1165
1166                 /*
1167                  * Insert AGG or GROUP node if needed, plus an explicit sort step
1168                  * if necessary.
1169                  *
1170                  * HAVING clause, if any, becomes qual of the Agg or Group node.
1171                  */
1172                 if (use_hashed_grouping)
1173                 {
1174                         /* Hashed aggregate plan --- no sort needed */
1175                         result_plan = (Plan *) make_agg(parse,
1176                                                                                         tlist,
1177                                                                                         (List *) parse->havingQual,
1178                                                                                         AGG_HASHED,
1179                                                                                         numGroupCols,
1180                                                                                         groupColIdx,
1181                                                                                         numGroups,
1182                                                                                         agg_counts.numAggs,
1183                                                                                         result_plan);
1184                         /* Hashed aggregation produces randomly-ordered results */
1185                         current_pathkeys = NIL;
1186                 }
1187                 else if (parse->hasAggs)
1188                 {
1189                         /* Plain aggregate plan --- sort if needed */
1190                         AggStrategy aggstrategy;
1191
1192                         if (parse->groupClause)
1193                         {
1194                                 if (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
1195                                 {
1196                                         result_plan = (Plan *)
1197                                                 make_sort_from_groupcols(parse,
1198                                                                                                  parse->groupClause,
1199                                                                                                  groupColIdx,
1200                                                                                                  result_plan);
1201                                         current_pathkeys = group_pathkeys;
1202                                 }
1203                                 aggstrategy = AGG_SORTED;
1204
1205                                 /*
1206                                  * The AGG node will not change the sort ordering of its
1207                                  * groups, so current_pathkeys describes the result too.
1208                                  */
1209                         }
1210                         else
1211                         {
1212                                 aggstrategy = AGG_PLAIN;
1213                                 /* Result will be only one row anyway; no sort order */
1214                                 current_pathkeys = NIL;
1215                         }
1216
1217                         result_plan = (Plan *) make_agg(parse,
1218                                                                                         tlist,
1219                                                                                         (List *) parse->havingQual,
1220                                                                                         aggstrategy,
1221                                                                                         numGroupCols,
1222                                                                                         groupColIdx,
1223                                                                                         numGroups,
1224                                                                                         agg_counts.numAggs,
1225                                                                                         result_plan);
1226                 }
1227                 else if (parse->groupClause)
1228                 {
1229                         /*
1230                          * GROUP BY without aggregation, so insert a group node (plus the
1231                          * appropriate sort node, if necessary).
1232                          *
1233                          * Add an explicit sort if we couldn't make the path come
1234                          * out the way the GROUP node needs it.
1235                          */
1236                         if (!pathkeys_contained_in(group_pathkeys, current_pathkeys))
1237                         {
1238                                 result_plan = (Plan *)
1239                                         make_sort_from_groupcols(parse,
1240                                                                                          parse->groupClause,
1241                                                                                          groupColIdx,
1242                                                                                          result_plan);
1243                                 current_pathkeys = group_pathkeys;
1244                         }
1245
1246                         result_plan = (Plan *) make_group(parse,
1247                                                                                           tlist,
1248                                                                                           (List *) parse->havingQual,
1249                                                                                           numGroupCols,
1250                                                                                           groupColIdx,
1251                                                                                           dNumGroups,
1252                                                                                           result_plan);
1253                         /* The Group node won't change sort ordering */
1254                 }
1255                 else if (parse->hasHavingQual)
1256                 {
1257                         /*
1258                          * No aggregates, and no GROUP BY, but we have a HAVING qual.
1259                          * This is a degenerate case in which we are supposed to emit
1260                          * either 0 or 1 row depending on whether HAVING succeeds.
1261                          * Furthermore, there cannot be any variables in either HAVING
1262                          * or the targetlist, so we actually do not need the FROM table
1263                          * at all!  We can just throw away the plan-so-far and generate
1264                          * a Result node.  This is a sufficiently unusual corner case
1265                          * that it's not worth contorting the structure of this routine
1266                          * to avoid having to generate the plan in the first place.
1267                          */
1268                         result_plan = (Plan *) make_result(tlist,
1269                                                                                            parse->havingQual,
1270                                                                                            NULL);
1271                 }
1272         }                                                       /* end of if (setOperations) */
1273
1274         /*
1275          * If we were not able to make the plan come out in the right order,
1276          * add an explicit sort step.
1277          */
1278         if (parse->sortClause)
1279         {
1280                 if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys))
1281                 {
1282                         result_plan = (Plan *)
1283                                 make_sort_from_sortclauses(parse,
1284                                                                                    parse->sortClause,
1285                                                                                    result_plan);
1286                         current_pathkeys = sort_pathkeys;
1287                 }
1288         }
1289
1290         /*
1291          * If there is a DISTINCT clause, add the UNIQUE node.
1292          */
1293         if (parse->distinctClause)
1294         {
1295                 result_plan = (Plan *) make_unique(result_plan, parse->distinctClause);
1296
1297                 /*
1298                  * If there was grouping or aggregation, leave plan_rows as-is
1299                  * (ie, assume the result was already mostly unique).  If not,
1300                  * it's reasonable to assume the UNIQUE filter has effects
1301                  * comparable to GROUP BY.
1302                  */
1303                 if (!parse->groupClause && !parse->hasHavingQual && !parse->hasAggs)
1304                 {
1305                         List       *distinctExprs;
1306
1307                         distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
1308                                                                                                         parse->targetList);
1309                         result_plan->plan_rows = estimate_num_groups(parse,
1310                                                                                                                  distinctExprs,
1311                                                                                                  result_plan->plan_rows);
1312                 }
1313         }
1314
1315         /*
1316          * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
1317          */
1318         if (parse->limitOffset || parse->limitCount)
1319         {
1320                 result_plan = (Plan *) make_limit(result_plan,
1321                                                                                   parse->limitOffset,
1322                                                                                   parse->limitCount);
1323         }
1324
1325         /*
1326          * Return the actual output ordering in query_pathkeys for possible
1327          * use by an outer query level.
1328          */
1329         parse->query_pathkeys = current_pathkeys;
1330
1331         return result_plan;
1332 }
1333
1334 /*
1335  * hash_safe_grouping - are grouping operators hashable?
1336  *
1337  * We assume hashed aggregation will work if the datatype's equality operator
1338  * is marked hashjoinable.
1339  */
1340 static bool
1341 hash_safe_grouping(Query *parse)
1342 {
1343         ListCell   *gl;
1344
1345         foreach(gl, parse->groupClause)
1346         {
1347                 GroupClause *grpcl = (GroupClause *) lfirst(gl);
1348                 TargetEntry *tle = get_sortgroupclause_tle(grpcl, parse->targetList);
1349                 Operator        optup;
1350                 bool            oprcanhash;
1351
1352                 optup = equality_oper(tle->resdom->restype, true);
1353                 if (!optup)
1354                         return false;
1355                 oprcanhash = ((Form_pg_operator) GETSTRUCT(optup))->oprcanhash;
1356                 ReleaseSysCache(optup);
1357                 if (!oprcanhash)
1358                         return false;
1359         }
1360         return true;
1361 }
1362
1363 /*---------------
1364  * make_subplanTargetList
1365  *        Generate appropriate target list when grouping is required.
1366  *
1367  * When grouping_planner inserts Aggregate, Group, or Result plan nodes
1368  * above the result of query_planner, we typically want to pass a different
1369  * target list to query_planner than the outer plan nodes should have.
1370  * This routine generates the correct target list for the subplan.
1371  *
1372  * The initial target list passed from the parser already contains entries
1373  * for all ORDER BY and GROUP BY expressions, but it will not have entries
1374  * for variables used only in HAVING clauses; so we need to add those
1375  * variables to the subplan target list.  Also, we flatten all expressions
1376  * except GROUP BY items into their component variables; the other expressions
1377  * will be computed by the inserted nodes rather than by the subplan.
1378  * For example, given a query like
1379  *              SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
1380  * we want to pass this targetlist to the subplan:
1381  *              a,b,c,d,a+b
1382  * where the a+b target will be used by the Sort/Group steps, and the
1383  * other targets will be used for computing the final results.  (In the
1384  * above example we could theoretically suppress the a and b targets and
1385  * pass down only c,d,a+b, but it's not really worth the trouble to
1386  * eliminate simple var references from the subplan.  We will avoid doing
1387  * the extra computation to recompute a+b at the outer level; see
1388  * replace_vars_with_subplan_refs() in setrefs.c.)
1389  *
1390  * If we are grouping or aggregating, *and* there are no non-Var grouping
1391  * expressions, then the returned tlist is effectively dummy; we do not
1392  * need to force it to be evaluated, because all the Vars it contains
1393  * should be present in the output of query_planner anyway.
1394  *
1395  * 'parse' is the query being processed.
1396  * 'tlist' is the query's target list.
1397  * 'groupColIdx' receives an array of column numbers for the GROUP BY
1398  *                      expressions (if there are any) in the subplan's target list.
1399  * 'need_tlist_eval' is set true if we really need to evaluate the
1400  *                      result tlist.
1401  *
1402  * The result is the targetlist to be passed to the subplan.
1403  *---------------
1404  */
1405 static List *
1406 make_subplanTargetList(Query *parse,
1407                                            List *tlist,
1408                                            AttrNumber **groupColIdx,
1409                                            bool *need_tlist_eval)
1410 {
1411         List       *sub_tlist;
1412         List       *extravars;
1413         int                     numCols;
1414
1415         *groupColIdx = NULL;
1416
1417         /*
1418          * If we're not grouping or aggregating, there's nothing to do here;
1419          * query_planner should receive the unmodified target list.
1420          */
1421         if (!parse->hasAggs && !parse->groupClause && !parse->hasHavingQual)
1422         {
1423                 *need_tlist_eval = true;
1424                 return tlist;
1425         }
1426
1427         /*
1428          * Otherwise, start with a "flattened" tlist (having just the vars
1429          * mentioned in the targetlist and HAVING qual --- but not upper-
1430          * level Vars; they will be replaced by Params later on).
1431          */
1432         sub_tlist = flatten_tlist(tlist);
1433         extravars = pull_var_clause(parse->havingQual, false);
1434         sub_tlist = add_to_flat_tlist(sub_tlist, extravars);
1435         list_free(extravars);
1436         *need_tlist_eval = false;       /* only eval if not flat tlist */
1437
1438         /*
1439          * If grouping, create sub_tlist entries for all GROUP BY expressions
1440          * (GROUP BY items that are simple Vars should be in the list
1441          * already), and make an array showing where the group columns are in
1442          * the sub_tlist.
1443          */
1444         numCols = list_length(parse->groupClause);
1445         if (numCols > 0)
1446         {
1447                 int                     keyno = 0;
1448                 AttrNumber *grpColIdx;
1449                 ListCell   *gl;
1450
1451                 grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
1452                 *groupColIdx = grpColIdx;
1453
1454                 foreach(gl, parse->groupClause)
1455                 {
1456                         GroupClause *grpcl = (GroupClause *) lfirst(gl);
1457                         Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1458                         TargetEntry *te = NULL;
1459                         ListCell   *sl;
1460
1461                         /* Find or make a matching sub_tlist entry */
1462                         foreach(sl, sub_tlist)
1463                         {
1464                                 te = (TargetEntry *) lfirst(sl);
1465                                 if (equal(groupexpr, te->expr))
1466                                         break;
1467                         }
1468                         if (!sl)
1469                         {
1470                                 te = makeTargetEntry(makeResdom(list_length(sub_tlist) + 1,
1471                                                                                                 exprType(groupexpr),
1472                                                                                                 exprTypmod(groupexpr),
1473                                                                                                 NULL,
1474                                                                                                 false),
1475                                                                          (Expr *) groupexpr);
1476                                 sub_tlist = lappend(sub_tlist, te);
1477                                 *need_tlist_eval = true;                /* it's not flat anymore */
1478                         }
1479
1480                         /* and save its resno */
1481                         grpColIdx[keyno++] = te->resdom->resno;
1482                 }
1483         }
1484
1485         return sub_tlist;
1486 }
1487
1488 /*
1489  * locate_grouping_columns
1490  *              Locate grouping columns in the tlist chosen by query_planner.
1491  *
1492  * This is only needed if we don't use the sub_tlist chosen by
1493  * make_subplanTargetList.      We have to forget the column indexes found
1494  * by that routine and re-locate the grouping vars in the real sub_tlist.
1495  */
1496 static void
1497 locate_grouping_columns(Query *parse,
1498                                                 List *tlist,
1499                                                 List *sub_tlist,
1500                                                 AttrNumber *groupColIdx)
1501 {
1502         int                     keyno = 0;
1503         ListCell   *gl;
1504
1505         /*
1506          * No work unless grouping.
1507          */
1508         if (!parse->groupClause)
1509         {
1510                 Assert(groupColIdx == NULL);
1511                 return;
1512         }
1513         Assert(groupColIdx != NULL);
1514
1515         foreach(gl, parse->groupClause)
1516         {
1517                 GroupClause *grpcl = (GroupClause *) lfirst(gl);
1518                 Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1519                 TargetEntry *te = NULL;
1520                 ListCell   *sl;
1521
1522                 foreach(sl, sub_tlist)
1523                 {
1524                         te = (TargetEntry *) lfirst(sl);
1525                         if (equal(groupexpr, te->expr))
1526                                 break;
1527                 }
1528                 if (!sl)
1529                         elog(ERROR, "failed to locate grouping columns");
1530
1531                 groupColIdx[keyno++] = te->resdom->resno;
1532         }
1533 }
1534
1535 /*
1536  * postprocess_setop_tlist
1537  *        Fix up targetlist returned by plan_set_operations().
1538  *
1539  * We need to transpose sort key info from the orig_tlist into new_tlist.
1540  * NOTE: this would not be good enough if we supported resjunk sort keys
1541  * for results of set operations --- then, we'd need to project a whole
1542  * new tlist to evaluate the resjunk columns.  For now, just ereport if we
1543  * find any resjunk columns in orig_tlist.
1544  */
1545 static List *
1546 postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
1547 {
1548         ListCell   *l;
1549         ListCell   *orig_tlist_item = list_head(orig_tlist);
1550
1551         foreach(l, new_tlist)
1552         {
1553                 TargetEntry *new_tle = (TargetEntry *) lfirst(l);
1554                 TargetEntry *orig_tle;
1555
1556                 /* ignore resjunk columns in setop result */
1557                 if (new_tle->resdom->resjunk)
1558                         continue;
1559
1560                 Assert(orig_tlist_item != NULL);
1561                 orig_tle = (TargetEntry *) lfirst(orig_tlist_item);
1562                 orig_tlist_item = lnext(orig_tlist_item);
1563                 if (orig_tle->resdom->resjunk)  /* should not happen */
1564                         elog(ERROR, "resjunk output columns are not implemented");
1565                 Assert(new_tle->resdom->resno == orig_tle->resdom->resno);
1566                 Assert(new_tle->resdom->restype == orig_tle->resdom->restype);
1567                 new_tle->resdom->ressortgroupref = orig_tle->resdom->ressortgroupref;
1568         }
1569         if (orig_tlist_item != NULL)
1570                 elog(ERROR, "resjunk output columns are not implemented");
1571         return new_tlist;
1572 }