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) 1996-2008, 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 1.235 2008/07/31 22:47:56 tgl Exp $
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15
  16 #include "postgres.h"
  17
  18 #include <limits.h>
  19
  20 #include "catalog/pg_operator.h"
  21 #include "executor/executor.h"
  22 #include "executor/nodeAgg.h"
  23 #include "miscadmin.h"
  24 #include "nodes/makefuncs.h"
  25 #include "optimizer/clauses.h"
  26 #include "optimizer/cost.h"
  27 #include "optimizer/pathnode.h"
  28 #include "optimizer/paths.h"
  29 #include "optimizer/planmain.h"
  30 #include "optimizer/planner.h"
  31 #include "optimizer/prep.h"
  32 #include "optimizer/subselect.h"
  33 #include "optimizer/tlist.h"
  34 #include "optimizer/var.h"
  35 #ifdef OPTIMIZER_DEBUG
  36 #include "nodes/print.h"
  37 #endif
  38 #include "parser/parse_expr.h"
  39 #include "parser/parse_oper.h"
  40 #include "parser/parsetree.h"
  41 #include "utils/lsyscache.h"
  42 #include "utils/syscache.h"
  43
  44
  45 /* GUC parameter */
  46 double cursor_tuple_fraction = DEFAULT_CURSOR_TUPLE_FRACTION;
  47
  48 /* Hook for plugins to get control in planner() */
  49 planner_hook_type planner_hook = NULL;
  50
  51
  52 /* Expression kind codes for preprocess_expression */
  53 #define EXPRKIND_QUAL           0
  54 #define EXPRKIND_TARGET         1
  55 #define EXPRKIND_RTFUNC         2
  56 #define EXPRKIND_VALUES         3
  57 #define EXPRKIND_LIMIT          4
  58 #define EXPRKIND_ININFO         5
  59 #define EXPRKIND_APPINFO        6
  60
  61
  62 static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
  63 static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
  64 static Plan *inheritance_planner(PlannerInfo *root);
  65 static Plan *grouping_planner(PlannerInfo *root, double tuple_fraction);
  66 static bool is_dummy_plan(Plan *plan);
  67 static double preprocess_limit(PlannerInfo *root,
  68                                  double tuple_fraction,
  69                                  int64 *offset_est, int64 *count_est);
  70 static Oid *extract_grouping_ops(List *groupClause);
  71 static bool choose_hashed_grouping(PlannerInfo *root,
  72                                            double tuple_fraction, double limit_tuples,
  73                                            Path *cheapest_path, Path *sorted_path,
  74                                            Oid *groupOperators, double dNumGroups,
  75                                            AggClauseCounts *agg_counts);
  76 static List *make_subplanTargetList(PlannerInfo *root, List *tlist,
  77                                            AttrNumber **groupColIdx, bool *need_tlist_eval);
  78 static void locate_grouping_columns(PlannerInfo *root,
  79                                                 List *tlist,
  80                                                 List *sub_tlist,
  81                                                 AttrNumber *groupColIdx);
  82 static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
  83
  84
  85 /*****************************************************************************
  86  *
  87  *         Query optimizer entry point
  88  *
  89  * To support loadable plugins that monitor or modify planner behavior,
  90  * we provide a hook variable that lets a plugin get control before and
  91  * after the standard planning process.  The plugin would normally call
  92  * standard_planner().
  93  *
  94  * Note to plugin authors: standard_planner() scribbles on its Query input,
  95  * so you'd better copy that data structure if you want to plan more than once.
  96  *
  97  *****************************************************************************/
  98 PlannedStmt *
  99 planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 100 {
 101         PlannedStmt *result;
 102
 103         if (planner_hook)
 104                 result = (*planner_hook) (parse, cursorOptions, boundParams);
 105         else
 106                 result = standard_planner(parse, cursorOptions, boundParams);
 107         return result;
 108 }
 109
 110 PlannedStmt *
 111 standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 112 {
 113         PlannedStmt *result;
 114         PlannerGlobal *glob;
 115         double          tuple_fraction;
 116         PlannerInfo *root;
 117         Plan       *top_plan;
 118         ListCell   *lp,
 119                            *lr;
 120
 121         /* Cursor options may come from caller or from DECLARE CURSOR stmt */
 122         if (parse->utilityStmt &&
 123                 IsA(parse->utilityStmt, DeclareCursorStmt))
 124                 cursorOptions |= ((DeclareCursorStmt *) parse->utilityStmt)->options;
 125
 126         /*
 127          * Set up global state for this planner invocation.  This data is needed
 128          * across all levels of sub-Query that might exist in the given command,
 129          * so we keep it in a separate struct that's linked to by each per-Query
 130          * PlannerInfo.
 131          */
 132         glob = makeNode(PlannerGlobal);
 133
 134         glob->boundParams = boundParams;
 135         glob->paramlist = NIL;
 136         glob->subplans = NIL;
 137         glob->subrtables = NIL;
 138         glob->rewindPlanIDs = NULL;
 139         glob->finalrtable = NIL;
 140         glob->relationOids = NIL;
 141         glob->transientPlan = false;
 142
 143         /* Determine what fraction of the plan is likely to be scanned */
 144         if (cursorOptions & CURSOR_OPT_FAST_PLAN)
 145         {
 146                 /*
 147                  * We have no real idea how many tuples the user will ultimately FETCH
 148                  * from a cursor, but it is often the case that he doesn't want 'em
 149                  * all, or would prefer a fast-start plan anyway so that he can
 150                  * process some of the tuples sooner.  Use a GUC parameter to decide
 151                  * what fraction to optimize for.
 152                  */
 153                 tuple_fraction = cursor_tuple_fraction;
 154
 155                 /*
 156                  * We document cursor_tuple_fraction as simply being a fraction,
 157                  * which means the edge cases 0 and 1 have to be treated specially
 158                  * here.  We convert 1 to 0 ("all the tuples") and 0 to a very small
 159                  * fraction.
 160                  */
 161                 if (tuple_fraction >= 1.0)
 162                         tuple_fraction = 0.0;
 163                 else if (tuple_fraction <= 0.0)
 164                         tuple_fraction = 1e-10;
 165         }
 166         else
 167         {
 168                 /* Default assumption is we need all the tuples */
 169                 tuple_fraction = 0.0;
 170         }
 171
 172         /* primary planning entry point (may recurse for subqueries) */
 173         top_plan = subquery_planner(glob, parse, 1, tuple_fraction, &root);
 174
 175         /*
 176          * If creating a plan for a scrollable cursor, make sure it can run
 177          * backwards on demand.  Add a Material node at the top at need.
 178          */
 179         if (cursorOptions & CURSOR_OPT_SCROLL)
 180         {
 181                 if (!ExecSupportsBackwardScan(top_plan))
 182                         top_plan = materialize_finished_plan(top_plan);
 183         }
 184
 185         /* final cleanup of the plan */
 186         Assert(glob->finalrtable == NIL);
 187         top_plan = set_plan_references(glob, top_plan, root->parse->rtable);
 188         /* ... and the subplans (both regular subplans and initplans) */
 189         Assert(list_length(glob->subplans) == list_length(glob->subrtables));
 190         forboth(lp, glob->subplans, lr, glob->subrtables)
 191         {
 192                 Plan       *subplan = (Plan *) lfirst(lp);
 193                 List       *subrtable = (List *) lfirst(lr);
 194
 195                 lfirst(lp) = set_plan_references(glob, subplan, subrtable);
 196         }
 197
 198         /* build the PlannedStmt result */
 199         result = makeNode(PlannedStmt);
 200
 201         result->commandType = parse->commandType;
 202         result->canSetTag = parse->canSetTag;
 203         result->transientPlan = glob->transientPlan;
 204         result->planTree = top_plan;
 205         result->rtable = glob->finalrtable;
 206         result->resultRelations = root->resultRelations;
 207         result->utilityStmt = parse->utilityStmt;
 208         result->intoClause = parse->intoClause;
 209         result->subplans = glob->subplans;
 210         result->rewindPlanIDs = glob->rewindPlanIDs;
 211         result->returningLists = root->returningLists;
 212         result->rowMarks = parse->rowMarks;
 213         result->relationOids = glob->relationOids;
 214         result->nParamExec = list_length(glob->paramlist);
 215
 216         return result;
 217 }
 218
 219
 220 /*--------------------
 221  * subquery_planner
 222  *        Invokes the planner on a subquery.  We recurse to here for each
 223  *        sub-SELECT found in the query tree.
 224  *
 225  * glob is the global state for the current planner run.
 226  * parse is the querytree produced by the parser & rewriter.
 227  * level is the current recursion depth (1 at the top-level Query).
 228  * tuple_fraction is the fraction of tuples we expect will be retrieved.
 229  * tuple_fraction is interpreted as explained for grouping_planner, below.
 230  *
 231  * If subroot isn't NULL, we pass back the query's final PlannerInfo struct;
 232  * among other things this tells the output sort ordering of the plan.
 233  *
 234  * Basically, this routine does the stuff that should only be done once
 235  * per Query object.  It then calls grouping_planner.  At one time,
 236  * grouping_planner could be invoked recursively on the same Query object;
 237  * that's not currently true, but we keep the separation between the two
 238  * routines anyway, in case we need it again someday.
 239  *
 240  * subquery_planner will be called recursively to handle sub-Query nodes
 241  * found within the query's expressions and rangetable.
 242  *
 243  * Returns a query plan.
 244  *--------------------
 245  */
 246 Plan *
 247 subquery_planner(PlannerGlobal *glob, Query *parse,
 248                                  Index level, double tuple_fraction,
 249                                  PlannerInfo **subroot)
 250 {
 251         int                     num_old_subplans = list_length(glob->subplans);
 252         PlannerInfo *root;
 253         Plan       *plan;
 254         List       *newHaving;
 255         ListCell   *l;
 256
 257         /* Create a PlannerInfo data structure for this subquery */
 258         root = makeNode(PlannerInfo);
 259         root->parse = parse;
 260         root->glob = glob;
 261         root->query_level = level;
 262         root->planner_cxt = CurrentMemoryContext;
 263         root->init_plans = NIL;
 264         root->eq_classes = NIL;
 265         root->in_info_list = NIL;
 266         root->append_rel_list = NIL;
 267
 268         /*
 269          * Look for IN clauses at the top level of WHERE, and transform them into
 270          * joins.  Note that this step only handles IN clauses originally at top
 271          * level of WHERE; if we pull up any subqueries below, their INs are
 272          * processed just before pulling them up.
 273          */
 274         if (parse->hasSubLinks)
 275                 parse->jointree->quals = pull_up_IN_clauses(root,
 276                                                                                                         parse->jointree->quals);
 277
 278         /*
 279          * Scan the rangetable for set-returning functions, and inline them
 280          * if possible (producing subqueries that might get pulled up next).
 281          * Recursion issues here are handled in the same way as for IN clauses.
 282          */
 283         inline_set_returning_functions(root);
 284
 285         /*
 286          * Check to see if any subqueries in the rangetable can be merged into
 287          * this query.
 288          */
 289         parse->jointree = (FromExpr *)
 290                 pull_up_subqueries(root, (Node *) parse->jointree, false, false);
 291
 292         /*
 293          * Detect whether any rangetable entries are RTE_JOIN kind; if not, we can
 294          * avoid the expense of doing flatten_join_alias_vars().  Also check for
 295          * outer joins --- if none, we can skip reduce_outer_joins() and some
 296          * other processing.  This must be done after we have done
 297          * pull_up_subqueries, of course.
 298          *
 299          * Note: if reduce_outer_joins manages to eliminate all outer joins,
 300          * root->hasOuterJoins is not reset currently.  This is OK since its
 301          * purpose is merely to suppress unnecessary processing in simple cases.
 302          */
 303         root->hasJoinRTEs = false;
 304         root->hasOuterJoins = false;
 305         foreach(l, parse->rtable)
 306         {
 307                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 308
 309                 if (rte->rtekind == RTE_JOIN)
 310                 {
 311                         root->hasJoinRTEs = true;
 312                         if (IS_OUTER_JOIN(rte->jointype))
 313                         {
 314                                 root->hasOuterJoins = true;
 315                                 /* Can quit scanning once we find an outer join */
 316                                 break;
 317                         }
 318                 }
 319         }
 320
 321         /*
 322          * Expand any rangetable entries that are inheritance sets into "append
 323          * relations".  This can add entries to the rangetable, but they must be
 324          * plain base relations not joins, so it's OK (and marginally more
 325          * efficient) to do it after checking for join RTEs.  We must do it after
 326          * pulling up subqueries, else we'd fail to handle inherited tables in
 327          * subqueries.
 328          */
 329         expand_inherited_tables(root);
 330
 331         /*
 332          * Set hasHavingQual to remember if HAVING clause is present.  Needed
 333          * because preprocess_expression will reduce a constant-true condition to
 334          * an empty qual list ... but "HAVING TRUE" is not a semantic no-op.
 335          */
 336         root->hasHavingQual = (parse->havingQual != NULL);
 337
 338         /* Clear this flag; might get set in distribute_qual_to_rels */
 339         root->hasPseudoConstantQuals = false;
 340
 341         /*
 342          * Do expression preprocessing on targetlist and quals.
 343          */
 344         parse->targetList = (List *)
 345                 preprocess_expression(root, (Node *) parse->targetList,
 346                                                           EXPRKIND_TARGET);
 347
 348         parse->returningList = (List *)
 349                 preprocess_expression(root, (Node *) parse->returningList,
 350                                                           EXPRKIND_TARGET);
 351
 352         preprocess_qual_conditions(root, (Node *) parse->jointree);
 353
 354         parse->havingQual = preprocess_expression(root, parse->havingQual,
 355                                                                                           EXPRKIND_QUAL);
 356
 357         parse->limitOffset = preprocess_expression(root, parse->limitOffset,
 358                                                                                            EXPRKIND_LIMIT);
 359         parse->limitCount = preprocess_expression(root, parse->limitCount,
 360                                                                                           EXPRKIND_LIMIT);
 361
 362         root->in_info_list = (List *)
 363                 preprocess_expression(root, (Node *) root->in_info_list,
 364                                                           EXPRKIND_ININFO);
 365         root->append_rel_list = (List *)
 366                 preprocess_expression(root, (Node *) root->append_rel_list,
 367                                                           EXPRKIND_APPINFO);
 368
 369         /* Also need to preprocess expressions for function and values RTEs */
 370         foreach(l, parse->rtable)
 371         {
 372                 RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
 373
 374                 if (rte->rtekind == RTE_FUNCTION)
 375                         rte->funcexpr = preprocess_expression(root, rte->funcexpr,
 376                                                                                                   EXPRKIND_RTFUNC);
 377                 else if (rte->rtekind == RTE_VALUES)
 378                         rte->values_lists = (List *)
 379                                 preprocess_expression(root, (Node *) rte->values_lists,
 380                                                                           EXPRKIND_VALUES);
 381         }
 382
 383         /*
 384          * In some cases we may want to transfer a HAVING clause into WHERE. We
 385          * cannot do so if the HAVING clause contains aggregates (obviously) or
 386          * volatile functions (since a HAVING clause is supposed to be executed
 387          * only once per group).  Also, it may be that the clause is so expensive
 388          * to execute that we're better off doing it only once per group, despite
 389          * the loss of selectivity.  This is hard to estimate short of doing the
 390          * entire planning process twice, so we use a heuristic: clauses
 391          * containing subplans are left in HAVING.      Otherwise, we move or copy the
 392          * HAVING clause into WHERE, in hopes of eliminating tuples before
 393          * aggregation instead of after.
 394          *
 395          * If the query has explicit grouping then we can simply move such a
 396          * clause into WHERE; any group that fails the clause will not be in the
 397          * output because none of its tuples will reach the grouping or
 398          * aggregation stage.  Otherwise we must have a degenerate (variable-free)
 399          * HAVING clause, which we put in WHERE so that query_planner() can use it
 400          * in a gating Result node, but also keep in HAVING to ensure that we
 401          * don't emit a bogus aggregated row. (This could be done better, but it
 402          * seems not worth optimizing.)
 403          *
 404          * Note that both havingQual and parse->jointree->quals are in
 405          * implicitly-ANDed-list form at this point, even though they are declared
 406          * as Node *.
 407          */
 408         newHaving = NIL;
 409         foreach(l, (List *) parse->havingQual)
 410         {
 411                 Node       *havingclause = (Node *) lfirst(l);
 412
 413                 if (contain_agg_clause(havingclause) ||
 414                         contain_volatile_functions(havingclause) ||
 415                         contain_subplans(havingclause))
 416                 {
 417                         /* keep it in HAVING */
 418                         newHaving = lappend(newHaving, havingclause);
 419                 }
 420                 else if (parse->groupClause)
 421                 {
 422                         /* move it to WHERE */
 423                         parse->jointree->quals = (Node *)
 424                                 lappend((List *) parse->jointree->quals, havingclause);
 425                 }
 426                 else
 427                 {
 428                         /* put a copy in WHERE, keep it in HAVING */
 429                         parse->jointree->quals = (Node *)
 430                                 lappend((List *) parse->jointree->quals,
 431                                                 copyObject(havingclause));
 432                         newHaving = lappend(newHaving, havingclause);
 433                 }
 434         }
 435         parse->havingQual = (Node *) newHaving;
 436
 437         /*
 438          * If we have any outer joins, try to reduce them to plain inner joins.
 439          * This step is most easily done after we've done expression
 440          * preprocessing.
 441          */
 442         if (root->hasOuterJoins)
 443                 reduce_outer_joins(root);
 444
 445         /*
 446          * Do the main planning.  If we have an inherited target relation, that
 447          * needs special processing, else go straight to grouping_planner.
 448          */
 449         if (parse->resultRelation &&
 450                 rt_fetch(parse->resultRelation, parse->rtable)->inh)
 451                 plan = inheritance_planner(root);
 452         else
 453                 plan = grouping_planner(root, tuple_fraction);
 454
 455         /*
 456          * If any subplans were generated, or if we're inside a subplan, build
 457          * initPlan list and extParam/allParam sets for plan nodes, and attach the
 458          * initPlans to the top plan node.
 459          */
 460         if (list_length(glob->subplans) != num_old_subplans ||
 461                 root->query_level > 1)
 462                 SS_finalize_plan(root, plan, true);
 463
 464         /* Return internal info if caller wants it */
 465         if (subroot)
 466                 *subroot = root;
 467
 468         return plan;
 469 }
 470
 471 /*
 472  * preprocess_expression
 473  *              Do subquery_planner's preprocessing work for an expression,
 474  *              which can be a targetlist, a WHERE clause (including JOIN/ON
 475  *              conditions), or a HAVING clause.
 476  */
 477 static Node *
 478 preprocess_expression(PlannerInfo *root, Node *expr, int kind)
 479 {
 480         /*
 481          * Fall out quickly if expression is empty.  This occurs often enough to
 482          * be worth checking.  Note that null->null is the correct conversion for
 483          * implicit-AND result format, too.
 484          */
 485         if (expr == NULL)
 486                 return NULL;
 487
 488         /*
 489          * If the query has any join RTEs, replace join alias variables with
 490          * base-relation variables. We must do this before sublink processing,
 491          * else sublinks expanded out from join aliases wouldn't get processed. We
 492          * can skip it in VALUES lists, however, since they can't contain any Vars
 493          * at all.
 494          */
 495         if (root->hasJoinRTEs && kind != EXPRKIND_VALUES)
 496                 expr = flatten_join_alias_vars(root, expr);
 497
 498         /*
 499          * Simplify constant expressions.
 500          *
 501          * Note: this also flattens nested AND and OR expressions into N-argument
 502          * form.  All processing of a qual expression after this point must be
 503          * careful to maintain AND/OR flatness --- that is, do not generate a tree
 504          * with AND directly under AND, nor OR directly under OR.
 505          *
 506          * Because this is a relatively expensive process, we skip it when the
 507          * query is trivial, such as "SELECT 2+2;" or "INSERT ... VALUES()". The
 508          * expression will only be evaluated once anyway, so no point in
 509          * pre-simplifying; we can't execute it any faster than the executor can,
 510          * and we will waste cycles copying the tree.  Notice however that we
 511          * still must do it for quals (to get AND/OR flatness); and if we are in a
 512          * subquery we should not assume it will be done only once.
 513          *
 514          * For VALUES lists we never do this at all, again on the grounds that we
 515          * should optimize for one-time evaluation.
 516          */
 517         if (kind != EXPRKIND_VALUES &&
 518                 (root->parse->jointree->fromlist != NIL ||
 519                  kind == EXPRKIND_QUAL ||
 520                  root->query_level > 1))
 521                 expr = eval_const_expressions(root, expr);
 522
 523         /*
 524          * If it's a qual or havingQual, canonicalize it.
 525          */
 526         if (kind == EXPRKIND_QUAL)
 527         {
 528                 expr = (Node *) canonicalize_qual((Expr *) expr);
 529
 530 #ifdef OPTIMIZER_DEBUG
 531                 printf("After canonicalize_qual()\n");
 532                 pprint(expr);
 533 #endif
 534         }
 535
 536         /* Expand SubLinks to SubPlans */
 537         if (root->parse->hasSubLinks)
 538                 expr = SS_process_sublinks(root, expr, (kind == EXPRKIND_QUAL));
 539
 540         /*
 541          * XXX do not insert anything here unless you have grokked the comments in
 542          * SS_replace_correlation_vars ...
 543          */
 544
 545         /* Replace uplevel vars with Param nodes (this IS possible in VALUES) */
 546         if (root->query_level > 1)
 547                 expr = SS_replace_correlation_vars(root, expr);
 548
 549         /*
 550          * If it's a qual or havingQual, convert it to implicit-AND format. (We
 551          * don't want to do this before eval_const_expressions, since the latter
 552          * would be unable to simplify a top-level AND correctly. Also,
 553          * SS_process_sublinks expects explicit-AND format.)
 554          */
 555         if (kind == EXPRKIND_QUAL)
 556                 expr = (Node *) make_ands_implicit((Expr *) expr);
 557
 558         return expr;
 559 }
 560
 561 /*
 562  * preprocess_qual_conditions
 563  *              Recursively scan the query's jointree and do subquery_planner's
 564  *              preprocessing work on each qual condition found therein.
 565  */
 566 static void
 567 preprocess_qual_conditions(PlannerInfo *root, Node *jtnode)
 568 {
 569         if (jtnode == NULL)
 570                 return;
 571         if (IsA(jtnode, RangeTblRef))
 572         {
 573                 /* nothing to do here */
 574         }
 575         else if (IsA(jtnode, FromExpr))
 576         {
 577                 FromExpr   *f = (FromExpr *) jtnode;
 578                 ListCell   *l;
 579
 580                 foreach(l, f->fromlist)
 581                         preprocess_qual_conditions(root, lfirst(l));
 582
 583                 f->quals = preprocess_expression(root, f->quals, EXPRKIND_QUAL);
 584         }
 585         else if (IsA(jtnode, JoinExpr))
 586         {
 587                 JoinExpr   *j = (JoinExpr *) jtnode;
 588
 589                 preprocess_qual_conditions(root, j->larg);
 590                 preprocess_qual_conditions(root, j->rarg);
 591
 592                 j->quals = preprocess_expression(root, j->quals, EXPRKIND_QUAL);
 593         }
 594         else
 595                 elog(ERROR, "unrecognized node type: %d",
 596                          (int) nodeTag(jtnode));
 597 }
 598
 599 /*
 600  * inheritance_planner
 601  *        Generate a plan in the case where the result relation is an
 602  *        inheritance set.
 603  *
 604  * We have to handle this case differently from cases where a source relation
 605  * is an inheritance set. Source inheritance is expanded at the bottom of the
 606  * plan tree (see allpaths.c), but target inheritance has to be expanded at
 607  * the top.  The reason is that for UPDATE, each target relation needs a
 608  * different targetlist matching its own column set.  Also, for both UPDATE
 609  * and DELETE, the executor needs the Append plan node at the top, else it
 610  * can't keep track of which table is the current target table.  Fortunately,
 611  * the UPDATE/DELETE target can never be the nullable side of an outer join,
 612  * so it's OK to generate the plan this way.
 613  *
 614  * Returns a query plan.
 615  */
 616 static Plan *
 617 inheritance_planner(PlannerInfo *root)
 618 {
 619         Query      *parse = root->parse;
 620         int                     parentRTindex = parse->resultRelation;
 621         List       *subplans = NIL;
 622         List       *resultRelations = NIL;
 623         List       *returningLists = NIL;
 624         List       *rtable = NIL;
 625         List       *tlist = NIL;
 626         PlannerInfo subroot;
 627         ListCell   *l;
 628
 629         foreach(l, root->append_rel_list)
 630         {
 631                 AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
 632                 Plan       *subplan;
 633
 634                 /* append_rel_list contains all append rels; ignore others */
 635                 if (appinfo->parent_relid != parentRTindex)
 636                         continue;
 637
 638                 /*
 639                  * Generate modified query with this rel as target.  We have to be
 640                  * prepared to translate varnos in in_info_list as well as in the
 641                  * Query proper.
 642                  */
 643                 memcpy(&subroot, root, sizeof(PlannerInfo));
 644                 subroot.parse = (Query *)
 645                         adjust_appendrel_attrs((Node *) parse,
 646                                                                    appinfo);
 647                 subroot.in_info_list = (List *)
 648                         adjust_appendrel_attrs((Node *) root->in_info_list,
 649                                                                    appinfo);
 650                 subroot.init_plans = NIL;
 651                 /* There shouldn't be any OJ info to translate, as yet */
 652                 Assert(subroot.oj_info_list == NIL);
 653
 654                 /* Generate plan */
 655                 subplan = grouping_planner(&subroot, 0.0 /* retrieve all tuples */ );
 656
 657                 /*
 658                  * If this child rel was excluded by constraint exclusion, exclude it
 659                  * from the plan.
 660                  */
 661                 if (is_dummy_plan(subplan))
 662                         continue;
 663
 664                 /* Save rtable and tlist from first rel for use below */
 665                 if (subplans == NIL)
 666                 {
 667                         rtable = subroot.parse->rtable;
 668                         tlist = subplan->targetlist;
 669                 }
 670
 671                 subplans = lappend(subplans, subplan);
 672
 673                 /* Make sure any initplans from this rel get into the outer list */
 674                 root->init_plans = list_concat(root->init_plans, subroot.init_plans);
 675
 676                 /* Build target-relations list for the executor */
 677                 resultRelations = lappend_int(resultRelations, appinfo->child_relid);
 678
 679                 /* Build list of per-relation RETURNING targetlists */
 680                 if (parse->returningList)
 681                 {
 682                         Assert(list_length(subroot.returningLists) == 1);
 683                         returningLists = list_concat(returningLists,
 684                                                                                  subroot.returningLists);
 685                 }
 686         }
 687
 688         root->resultRelations = resultRelations;
 689         root->returningLists = returningLists;
 690
 691         /* Mark result as unordered (probably unnecessary) */
 692         root->query_pathkeys = NIL;
 693
 694         /*
 695          * If we managed to exclude every child rel, return a dummy plan
 696          */
 697         if (subplans == NIL)
 698         {
 699                 root->resultRelations = list_make1_int(parentRTindex);
 700                 /* although dummy, it must have a valid tlist for executor */
 701                 tlist = preprocess_targetlist(root, parse->targetList);
 702                 return (Plan *) make_result(root,
 703                                                                         tlist,
 704                                                                         (Node *) list_make1(makeBoolConst(false,
 705                                                                                                                                           false)),
 706                                                                         NULL);
 707         }
 708
 709         /*
 710          * Planning might have modified the rangetable, due to changes of the
 711          * Query structures inside subquery RTEs.  We have to ensure that this
 712          * gets propagated back to the master copy.  But can't do this until we
 713          * are done planning, because all the calls to grouping_planner need
 714          * virgin sub-Queries to work from.  (We are effectively assuming that
 715          * sub-Queries will get planned identically each time, or at least that
 716          * the impacts on their rangetables will be the same each time.)
 717          *
 718          * XXX should clean this up someday
 719          */
 720         parse->rtable = rtable;
 721
 722         /* Suppress Append if there's only one surviving child rel */
 723         if (list_length(subplans) == 1)
 724                 return (Plan *) linitial(subplans);
 725
 726         return (Plan *) make_append(subplans, true, tlist);
 727 }
 728
 729 /*--------------------
 730  * grouping_planner
 731  *        Perform planning steps related to grouping, aggregation, etc.
 732  *        This primarily means adding top-level processing to the basic
 733  *        query plan produced by query_planner.
 734  *
 735  * tuple_fraction is the fraction of tuples we expect will be retrieved
 736  *
 737  * tuple_fraction is interpreted as follows:
 738  *        0: expect all tuples to be retrieved (normal case)
 739  *        0 < tuple_fraction < 1: expect the given fraction of tuples available
 740  *              from the plan to be retrieved
 741  *        tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 742  *              expected to be retrieved (ie, a LIMIT specification)
 743  *
 744  * Returns a query plan.  Also, root->query_pathkeys is returned as the
 745  * actual output ordering of the plan (in pathkey format).
 746  *--------------------
 747  */
 748 static Plan *
 749 grouping_planner(PlannerInfo *root, double tuple_fraction)
 750 {
 751         Query      *parse = root->parse;
 752         List       *tlist = parse->targetList;
 753         int64           offset_est = 0;
 754         int64           count_est = 0;
 755         double          limit_tuples = -1.0;
 756         Plan       *result_plan;
 757         List       *current_pathkeys;
 758         List       *sort_pathkeys;
 759         double          dNumGroups = 0;
 760
 761         /* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
 762         if (parse->limitCount || parse->limitOffset)
 763         {
 764                 tuple_fraction = preprocess_limit(root, tuple_fraction,
 765                                                                                   &offset_est, &count_est);
 766
 767                 /*
 768                  * If we have a known LIMIT, and don't have an unknown OFFSET, we can
 769                  * estimate the effects of using a bounded sort.
 770                  */
 771                 if (count_est > 0 && offset_est >= 0)
 772                         limit_tuples = (double) count_est + (double) offset_est;
 773         }
 774
 775         if (parse->setOperations)
 776         {
 777                 List       *set_sortclauses;
 778
 779                 /*
 780                  * If there's a top-level ORDER BY, assume we have to fetch all the
 781                  * tuples.      This might seem too simplistic given all the hackery below
 782                  * to possibly avoid the sort ... but a nonzero tuple_fraction is only
 783                  * of use to plan_set_operations() when the setop is UNION ALL, and
 784                  * the result of UNION ALL is always unsorted.
 785                  */
 786                 if (parse->sortClause)
 787                         tuple_fraction = 0.0;
 788
 789                 /*
 790                  * Construct the plan for set operations.  The result will not need
 791                  * any work except perhaps a top-level sort and/or LIMIT.
 792                  */
 793                 result_plan = plan_set_operations(root, tuple_fraction,
 794                                                                                   &set_sortclauses);
 795
 796                 /*
 797                  * Calculate pathkeys representing the sort order (if any) of the set
 798                  * operation's result.  We have to do this before overwriting the sort
 799                  * key information...
 800                  */
 801                 current_pathkeys = make_pathkeys_for_sortclauses(root,
 802                                                                                                                  set_sortclauses,
 803                                                                                                          result_plan->targetlist,
 804                                                                                                                  true);
 805
 806                 /*
 807                  * We should not need to call preprocess_targetlist, since we must be
 808                  * in a SELECT query node.      Instead, use the targetlist returned by
 809                  * plan_set_operations (since this tells whether it returned any
 810                  * resjunk columns!), and transfer any sort key information from the
 811                  * original tlist.
 812                  */
 813                 Assert(parse->commandType == CMD_SELECT);
 814
 815                 tlist = postprocess_setop_tlist(result_plan->targetlist, tlist);
 816
 817                 /*
 818                  * Can't handle FOR UPDATE/SHARE here (parser should have checked
 819                  * already, but let's make sure).
 820                  */
 821                 if (parse->rowMarks)
 822                         ereport(ERROR,
 823                                         (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 824                                          errmsg("SELECT FOR UPDATE/SHARE is not allowed with UNION/INTERSECT/EXCEPT")));
 825
 826                 /*
 827                  * Calculate pathkeys that represent result ordering requirements
 828                  */
 829                 Assert(parse->distinctClause == NIL);
 830                 sort_pathkeys = make_pathkeys_for_sortclauses(root,
 831                                                                                                           parse->sortClause,
 832                                                                                                           tlist,
 833                                                                                                           true);
 834         }
 835         else
 836         {
 837                 /* No set operations, do regular planning */
 838                 List       *sub_tlist;
 839                 List       *group_pathkeys;
 840                 AttrNumber *groupColIdx = NULL;
 841                 Oid                *groupOperators = NULL;
 842                 bool            need_tlist_eval = true;
 843                 QualCost        tlist_cost;
 844                 Path       *cheapest_path;
 845                 Path       *sorted_path;
 846                 Path       *best_path;
 847                 long            numGroups = 0;
 848                 AggClauseCounts agg_counts;
 849                 int                     numGroupCols = list_length(parse->groupClause);
 850                 bool            use_hashed_grouping = false;
 851
 852                 MemSet(&agg_counts, 0, sizeof(AggClauseCounts));
 853
 854                 /* Preprocess targetlist */
 855                 tlist = preprocess_targetlist(root, tlist);
 856
 857                 /*
 858                  * Generate appropriate target list for subplan; may be different from
 859                  * tlist if grouping or aggregation is needed.
 860                  */
 861                 sub_tlist = make_subplanTargetList(root, tlist,
 862                                                                                    &groupColIdx, &need_tlist_eval);
 863
 864                 /*
 865                  * Calculate pathkeys that represent grouping/ordering requirements.
 866                  * Stash them in PlannerInfo so that query_planner can canonicalize
 867                  * them after EquivalenceClasses have been formed.
 868                  *
 869                  * Note: for the moment, DISTINCT is always implemented via sort/uniq,
 870                  * and we set the sort_pathkeys to be the more rigorous of the
 871                  * DISTINCT and ORDER BY requirements.  This should be changed
 872                  * someday, but DISTINCT ON is a bit of a problem ...
 873                  */
 874                 root->group_pathkeys =
 875                         make_pathkeys_for_sortclauses(root,
 876                                                                                   parse->groupClause,
 877                                                                                   tlist,
 878                                                                                   false);
 879                 if (list_length(parse->distinctClause) > list_length(parse->sortClause))
 880                         root->sort_pathkeys =
 881                                 make_pathkeys_for_sortclauses(root,
 882                                                                                           parse->distinctClause,
 883                                                                                           tlist,
 884                                                                                           false);
 885                 else
 886                         root->sort_pathkeys =
 887                                 make_pathkeys_for_sortclauses(root,
 888                                                                                           parse->sortClause,
 889                                                                                           tlist,
 890                                                                                           false);
 891
 892                 /*
 893                  * Will need actual number of aggregates for estimating costs.
 894                  *
 895                  * Note: we do not attempt to detect duplicate aggregates here; a
 896                  * somewhat-overestimated count is okay for our present purposes.
 897                  *
 898                  * Note: think not that we can turn off hasAggs if we find no aggs. It
 899                  * is possible for constant-expression simplification to remove all
 900                  * explicit references to aggs, but we still have to follow the
 901                  * aggregate semantics (eg, producing only one output row).
 902                  */
 903                 if (parse->hasAggs)
 904                 {
 905                         count_agg_clauses((Node *) tlist, &agg_counts);
 906                         count_agg_clauses(parse->havingQual, &agg_counts);
 907                 }
 908
 909                 /*
 910                  * Figure out whether we need a sorted result from query_planner.
 911                  *
 912                  * If we have a GROUP BY clause, then we want a result sorted properly
 913                  * for grouping.  Otherwise, if there is an ORDER BY clause, we want
 914                  * to sort by the ORDER BY clause.      (Note: if we have both, and ORDER
 915                  * BY is a superset of GROUP BY, it would be tempting to request sort
 916                  * by ORDER BY --- but that might just leave us failing to exploit an
 917                  * available sort order at all. Needs more thought...)
 918                  */
 919                 if (root->group_pathkeys)
 920                         root->query_pathkeys = root->group_pathkeys;
 921                 else if (root->sort_pathkeys)
 922                         root->query_pathkeys = root->sort_pathkeys;
 923                 else
 924                         root->query_pathkeys = NIL;
 925
 926                 /*
 927                  * Generate the best unsorted and presorted paths for this Query (but
 928                  * note there may not be any presorted path).  query_planner will also
 929                  * estimate the number of groups in the query, and canonicalize all
 930                  * the pathkeys.
 931                  */
 932                 query_planner(root, sub_tlist, tuple_fraction, limit_tuples,
 933                                           &cheapest_path, &sorted_path, &dNumGroups);
 934
 935                 group_pathkeys = root->group_pathkeys;
 936                 sort_pathkeys = root->sort_pathkeys;
 937
 938                 /*
 939                  * If grouping, extract the grouping operators and decide whether we
 940                  * want to use hashed grouping.
 941                  */
 942                 if (parse->groupClause)
 943                 {
 944                         groupOperators = extract_grouping_ops(parse->groupClause);
 945                         use_hashed_grouping =
 946                                 choose_hashed_grouping(root, tuple_fraction, limit_tuples,
 947                                                                            cheapest_path, sorted_path,
 948                                                                            groupOperators, dNumGroups,
 949                                                                            &agg_counts);
 950
 951                         /* Also convert # groups to long int --- but 'ware overflow! */
 952                         numGroups = (long) Min(dNumGroups, (double) LONG_MAX);
 953                 }
 954
 955                 /*
 956                  * Select the best path.  If we are doing hashed grouping, we will
 957                  * always read all the input tuples, so use the cheapest-total path.
 958                  * Otherwise, trust query_planner's decision about which to use.
 959                  */
 960                 if (use_hashed_grouping || !sorted_path)
 961                         best_path = cheapest_path;
 962                 else
 963                         best_path = sorted_path;
 964
 965                 /*
 966                  * Check to see if it's possible to optimize MIN/MAX aggregates. If
 967                  * so, we will forget all the work we did so far to choose a "regular"
 968                  * path ... but we had to do it anyway to be able to tell which way is
 969                  * cheaper.
 970                  */
 971                 result_plan = optimize_minmax_aggregates(root,
 972                                                                                                  tlist,
 973                                                                                                  best_path);
 974                 if (result_plan != NULL)
 975                 {
 976                         /*
 977                          * optimize_minmax_aggregates generated the full plan, with the
 978                          * right tlist, and it has no sort order.
 979                          */
 980                         current_pathkeys = NIL;
 981                 }
 982                 else
 983                 {
 984                         /*
 985                          * Normal case --- create a plan according to query_planner's
 986                          * results.
 987                          */
 988                         bool    need_sort_for_grouping = false;
 989
 990                         result_plan = create_plan(root, best_path);
 991                         current_pathkeys = best_path->pathkeys;
 992
 993                         /* Detect if we'll need an explicit sort for grouping */
 994                         if (parse->groupClause && !use_hashed_grouping &&
 995                                 !pathkeys_contained_in(group_pathkeys, current_pathkeys))
 996                         {
 997                                 need_sort_for_grouping = true;
 998                                 /*
 999                                  * Always override query_planner's tlist, so that we don't
1000                                  * sort useless data from a "physical" tlist.
1001                                  */
1002                                 need_tlist_eval = true;
1003                         }
1004
1005                         /*
1006                          * create_plan() returns a plan with just a "flat" tlist of
1007                          * required Vars.  Usually we need to insert the sub_tlist as the
1008                          * tlist of the top plan node.  However, we can skip that if we
1009                          * determined that whatever query_planner chose to return will be
1010                          * good enough.
1011                          */
1012                         if (need_tlist_eval)
1013                         {
1014                                 /*
1015                                  * If the top-level plan node is one that cannot do expression
1016                                  * evaluation, we must insert a Result node to project the
1017                                  * desired tlist.
1018                                  */
1019                                 if (!is_projection_capable_plan(result_plan))
1020                                 {
1021                                         result_plan = (Plan *) make_result(root,
1022                                                                                                            sub_tlist,
1023                                                                                                            NULL,
1024                                                                                                            result_plan);
1025                                 }
1026                                 else
1027                                 {
1028                                         /*
1029                                          * Otherwise, just replace the subplan's flat tlist with
1030                                          * the desired tlist.
1031                                          */
1032                                         result_plan->targetlist = sub_tlist;
1033                                 }
1034
1035                                 /*
1036                                  * Also, account for the cost of evaluation of the sub_tlist.
1037                                  *
1038                                  * Up to now, we have only been dealing with "flat" tlists,
1039                                  * containing just Vars.  So their evaluation cost is zero
1040                                  * according to the model used by cost_qual_eval() (or if you
1041                                  * prefer, the cost is factored into cpu_tuple_cost).  Thus we
1042                                  * can avoid accounting for tlist cost throughout
1043                                  * query_planner() and subroutines.  But now we've inserted a
1044                                  * tlist that might contain actual operators, sub-selects, etc
1045                                  * --- so we'd better account for its cost.
1046                                  *
1047                                  * Below this point, any tlist eval cost for added-on nodes
1048                                  * should be accounted for as we create those nodes.
1049                                  * Presently, of the node types we can add on, only Agg and
1050                                  * Group project new tlists (the rest just copy their input
1051                                  * tuples) --- so make_agg() and make_group() are responsible
1052                                  * for computing the added cost.
1053                                  */
1054                                 cost_qual_eval(&tlist_cost, sub_tlist, root);
1055                                 result_plan->startup_cost += tlist_cost.startup;
1056                                 result_plan->total_cost += tlist_cost.startup +
1057                                         tlist_cost.per_tuple * result_plan->plan_rows;
1058                         }
1059                         else
1060                         {
1061                                 /*
1062                                  * Since we're using query_planner's tlist and not the one
1063                                  * make_subplanTargetList calculated, we have to refigure any
1064                                  * grouping-column indexes make_subplanTargetList computed.
1065                                  */
1066                                 locate_grouping_columns(root, tlist, result_plan->targetlist,
1067                                                                                 groupColIdx);
1068                         }
1069
1070                         /*
1071                          * Insert AGG or GROUP node if needed, plus an explicit sort step
1072                          * if necessary.
1073                          *
1074                          * HAVING clause, if any, becomes qual of the Agg or Group node.
1075                          */
1076                         if (use_hashed_grouping)
1077                         {
1078                                 /* Hashed aggregate plan --- no sort needed */
1079                                 result_plan = (Plan *) make_agg(root,
1080                                                                                                 tlist,
1081                                                                                                 (List *) parse->havingQual,
1082                                                                                                 AGG_HASHED,
1083                                                                                                 numGroupCols,
1084                                                                                                 groupColIdx,
1085                                                                                                 groupOperators,
1086                                                                                                 numGroups,
1087                                                                                                 agg_counts.numAggs,
1088                                                                                                 result_plan);
1089                                 /* Hashed aggregation produces randomly-ordered results */
1090                                 current_pathkeys = NIL;
1091                         }
1092                         else if (parse->hasAggs)
1093                         {
1094                                 /* Plain aggregate plan --- sort if needed */
1095                                 AggStrategy aggstrategy;
1096
1097                                 if (parse->groupClause)
1098                                 {
1099                                         if (need_sort_for_grouping)
1100                                         {
1101                                                 result_plan = (Plan *)
1102                                                         make_sort_from_groupcols(root,
1103                                                                                                          parse->groupClause,
1104                                                                                                          groupColIdx,
1105                                                                                                          result_plan);
1106                                                 current_pathkeys = group_pathkeys;
1107                                         }
1108                                         aggstrategy = AGG_SORTED;
1109
1110                                         /*
1111                                          * The AGG node will not change the sort ordering of its
1112                                          * groups, so current_pathkeys describes the result too.
1113                                          */
1114                                 }
1115                                 else
1116                                 {
1117                                         aggstrategy = AGG_PLAIN;
1118                                         /* Result will be only one row anyway; no sort order */
1119                                         current_pathkeys = NIL;
1120                                 }
1121
1122                                 result_plan = (Plan *) make_agg(root,
1123                                                                                                 tlist,
1124                                                                                                 (List *) parse->havingQual,
1125                                                                                                 aggstrategy,
1126                                                                                                 numGroupCols,
1127                                                                                                 groupColIdx,
1128                                                                                                 groupOperators,
1129                                                                                                 numGroups,
1130                                                                                                 agg_counts.numAggs,
1131                                                                                                 result_plan);
1132                         }
1133                         else if (parse->groupClause)
1134                         {
1135                                 /*
1136                                  * GROUP BY without aggregation, so insert a group node (plus
1137                                  * the appropriate sort node, if necessary).
1138                                  *
1139                                  * Add an explicit sort if we couldn't make the path come out
1140                                  * the way the GROUP node needs it.
1141                                  */
1142                                 if (need_sort_for_grouping)
1143                                 {
1144                                         result_plan = (Plan *)
1145                                                 make_sort_from_groupcols(root,
1146                                                                                                  parse->groupClause,
1147                                                                                                  groupColIdx,
1148                                                                                                  result_plan);
1149                                         current_pathkeys = group_pathkeys;
1150                                 }
1151
1152                                 result_plan = (Plan *) make_group(root,
1153                                                                                                   tlist,
1154                                                                                                   (List *) parse->havingQual,
1155                                                                                                   numGroupCols,
1156                                                                                                   groupColIdx,
1157                                                                                                   groupOperators,
1158                                                                                                   dNumGroups,
1159                                                                                                   result_plan);
1160                                 /* The Group node won't change sort ordering */
1161                         }
1162                         else if (root->hasHavingQual)
1163                         {
1164                                 /*
1165                                  * No aggregates, and no GROUP BY, but we have a HAVING qual.
1166                                  * This is a degenerate case in which we are supposed to emit
1167                                  * either 0 or 1 row depending on whether HAVING succeeds.
1168                                  * Furthermore, there cannot be any variables in either HAVING
1169                                  * or the targetlist, so we actually do not need the FROM
1170                                  * table at all!  We can just throw away the plan-so-far and
1171                                  * generate a Result node.      This is a sufficiently unusual
1172                                  * corner case that it's not worth contorting the structure of
1173                                  * this routine to avoid having to generate the plan in the
1174                                  * first place.
1175                                  */
1176                                 result_plan = (Plan *) make_result(root,
1177                                                                                                    tlist,
1178                                                                                                    parse->havingQual,
1179                                                                                                    NULL);
1180                         }
1181                 }                                               /* end of non-minmax-aggregate case */
1182         }                                                       /* end of if (setOperations) */
1183
1184         /*
1185          * If we were not able to make the plan come out in the right order, add
1186          * an explicit sort step.
1187          */
1188         if (sort_pathkeys)
1189         {
1190                 if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys))
1191                 {
1192                         result_plan = (Plan *) make_sort_from_pathkeys(root,
1193                                                                                                                    result_plan,
1194                                                                                                                    sort_pathkeys,
1195                                                                                                                    limit_tuples);
1196                         current_pathkeys = sort_pathkeys;
1197                 }
1198         }
1199
1200         /*
1201          * If there is a DISTINCT clause, add the UNIQUE node.
1202          */
1203         if (parse->distinctClause)
1204         {
1205                 result_plan = (Plan *) make_unique(result_plan, parse->distinctClause);
1206
1207                 /*
1208                  * If there was grouping or aggregation, leave plan_rows as-is (ie,
1209                  * assume the result was already mostly unique).  If not, use the
1210                  * number of distinct-groups calculated by query_planner.
1211                  */
1212                 if (!parse->groupClause && !root->hasHavingQual && !parse->hasAggs)
1213                         result_plan->plan_rows = dNumGroups;
1214         }
1215
1216         /*
1217          * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node.
1218          */
1219         if (parse->limitCount || parse->limitOffset)
1220         {
1221                 result_plan = (Plan *) make_limit(result_plan,
1222                                                                                   parse->limitOffset,
1223                                                                                   parse->limitCount,
1224                                                                                   offset_est,
1225                                                                                   count_est);
1226         }
1227
1228         /*
1229          * Deal with the RETURNING clause if any.  It's convenient to pass the
1230          * returningList through setrefs.c now rather than at top level (if we
1231          * waited, handling inherited UPDATE/DELETE would be much harder).
1232          */
1233         if (parse->returningList)
1234         {
1235                 List       *rlist;
1236
1237                 Assert(parse->resultRelation);
1238                 rlist = set_returning_clause_references(root->glob,
1239                                                                                                 parse->returningList,
1240                                                                                                 result_plan,
1241                                                                                                 parse->resultRelation);
1242                 root->returningLists = list_make1(rlist);
1243         }
1244         else
1245                 root->returningLists = NIL;
1246
1247         /* Compute result-relations list if needed */
1248         if (parse->resultRelation)
1249                 root->resultRelations = list_make1_int(parse->resultRelation);
1250         else
1251                 root->resultRelations = NIL;
1252
1253         /*
1254          * Return the actual output ordering in query_pathkeys for possible use by
1255          * an outer query level.
1256          */
1257         root->query_pathkeys = current_pathkeys;
1258
1259         return result_plan;
1260 }
1261
1262 /*
1263  * Detect whether a plan node is a "dummy" plan created when a relation
1264  * is deemed not to need scanning due to constraint exclusion.
1265  *
1266  * Currently, such dummy plans are Result nodes with constant FALSE
1267  * filter quals.
1268  */
1269 static bool
1270 is_dummy_plan(Plan *plan)
1271 {
1272         if (IsA(plan, Result))
1273         {
1274                 List       *rcqual = (List *) ((Result *) plan)->resconstantqual;
1275
1276                 if (list_length(rcqual) == 1)
1277                 {
1278                         Const      *constqual = (Const *) linitial(rcqual);
1279
1280                         if (constqual && IsA(constqual, Const))
1281                         {
1282                                 if (!constqual->constisnull &&
1283                                         !DatumGetBool(constqual->constvalue))
1284                                         return true;
1285                         }
1286                 }
1287         }
1288         return false;
1289 }
1290
1291 /*
1292  * preprocess_limit - do pre-estimation for LIMIT and/or OFFSET clauses
1293  *
1294  * We try to estimate the values of the LIMIT/OFFSET clauses, and pass the
1295  * results back in *count_est and *offset_est.  These variables are set to
1296  * 0 if the corresponding clause is not present, and -1 if it's present
1297  * but we couldn't estimate the value for it.  (The "0" convention is OK
1298  * for OFFSET but a little bit bogus for LIMIT: effectively we estimate
1299  * LIMIT 0 as though it were LIMIT 1.  But this is in line with the planner's
1300  * usual practice of never estimating less than one row.)  These values will
1301  * be passed to make_limit, which see if you change this code.
1302  *
1303  * The return value is the suitably adjusted tuple_fraction to use for
1304  * planning the query.  This adjustment is not overridable, since it reflects
1305  * plan actions that grouping_planner() will certainly take, not assumptions
1306  * about context.
1307  */
1308 static double
1309 preprocess_limit(PlannerInfo *root, double tuple_fraction,
1310                                  int64 *offset_est, int64 *count_est)
1311 {
1312         Query      *parse = root->parse;
1313         Node       *est;
1314         double          limit_fraction;
1315
1316         /* Should not be called unless LIMIT or OFFSET */
1317         Assert(parse->limitCount || parse->limitOffset);
1318
1319         /*
1320          * Try to obtain the clause values.  We use estimate_expression_value
1321          * primarily because it can sometimes do something useful with Params.
1322          */
1323         if (parse->limitCount)
1324         {
1325                 est = estimate_expression_value(root, parse->limitCount);
1326                 if (est && IsA(est, Const))
1327                 {
1328                         if (((Const *) est)->constisnull)
1329                         {
1330                                 /* NULL indicates LIMIT ALL, ie, no limit */
1331                                 *count_est = 0; /* treat as not present */
1332                         }
1333                         else
1334                         {
1335                                 *count_est = DatumGetInt64(((Const *) est)->constvalue);
1336                                 if (*count_est <= 0)
1337                                         *count_est = 1;         /* force to at least 1 */
1338                         }
1339                 }
1340                 else
1341                         *count_est = -1;        /* can't estimate */
1342         }
1343         else
1344                 *count_est = 0;                 /* not present */
1345
1346         if (parse->limitOffset)
1347         {
1348                 est = estimate_expression_value(root, parse->limitOffset);
1349                 if (est && IsA(est, Const))
1350                 {
1351                         if (((Const *) est)->constisnull)
1352                         {
1353                                 /* Treat NULL as no offset; the executor will too */
1354                                 *offset_est = 0;        /* treat as not present */
1355                         }
1356                         else
1357                         {
1358                                 *offset_est = DatumGetInt64(((Const *) est)->constvalue);
1359                                 if (*offset_est < 0)
1360                                         *offset_est = 0;        /* less than 0 is same as 0 */
1361                         }
1362                 }
1363                 else
1364                         *offset_est = -1;       /* can't estimate */
1365         }
1366         else
1367                 *offset_est = 0;                /* not present */
1368
1369         if (*count_est != 0)
1370         {
1371                 /*
1372                  * A LIMIT clause limits the absolute number of tuples returned.
1373                  * However, if it's not a constant LIMIT then we have to guess; for
1374                  * lack of a better idea, assume 10% of the plan's result is wanted.
1375                  */
1376                 if (*count_est < 0 || *offset_est < 0)
1377                 {
1378                         /* LIMIT or OFFSET is an expression ... punt ... */
1379                         limit_fraction = 0.10;
1380                 }
1381                 else
1382                 {
1383                         /* LIMIT (plus OFFSET, if any) is max number of tuples needed */
1384                         limit_fraction = (double) *count_est + (double) *offset_est;
1385                 }
1386
1387                 /*
1388                  * If we have absolute limits from both caller and LIMIT, use the
1389                  * smaller value; likewise if they are both fractional.  If one is
1390                  * fractional and the other absolute, we can't easily determine which
1391                  * is smaller, but we use the heuristic that the absolute will usually
1392                  * be smaller.
1393                  */
1394                 if (tuple_fraction >= 1.0)
1395                 {
1396                         if (limit_fraction >= 1.0)
1397                         {
1398                                 /* both absolute */
1399                                 tuple_fraction = Min(tuple_fraction, limit_fraction);
1400                         }
1401                         else
1402                         {
1403                                 /* caller absolute, limit fractional; use caller's value */
1404                         }
1405                 }
1406                 else if (tuple_fraction > 0.0)
1407                 {
1408                         if (limit_fraction >= 1.0)
1409                         {
1410                                 /* caller fractional, limit absolute; use limit */
1411                                 tuple_fraction = limit_fraction;
1412                         }
1413                         else
1414                         {
1415                                 /* both fractional */
1416                                 tuple_fraction = Min(tuple_fraction, limit_fraction);
1417                         }
1418                 }
1419                 else
1420                 {
1421                         /* no info from caller, just use limit */
1422                         tuple_fraction = limit_fraction;
1423                 }
1424         }
1425         else if (*offset_est != 0 && tuple_fraction > 0.0)
1426         {
1427                 /*
1428                  * We have an OFFSET but no LIMIT.      This acts entirely differently
1429                  * from the LIMIT case: here, we need to increase rather than decrease
1430                  * the caller's tuple_fraction, because the OFFSET acts to cause more
1431                  * tuples to be fetched instead of fewer.  This only matters if we got
1432                  * a tuple_fraction > 0, however.
1433                  *
1434                  * As above, use 10% if OFFSET is present but unestimatable.
1435                  */
1436                 if (*offset_est < 0)
1437                         limit_fraction = 0.10;
1438                 else
1439                         limit_fraction = (double) *offset_est;
1440
1441                 /*
1442                  * If we have absolute counts from both caller and OFFSET, add them
1443                  * together; likewise if they are both fractional.      If one is
1444                  * fractional and the other absolute, we want to take the larger, and
1445                  * we heuristically assume that's the fractional one.
1446                  */
1447                 if (tuple_fraction >= 1.0)
1448                 {
1449                         if (limit_fraction >= 1.0)
1450                         {
1451                                 /* both absolute, so add them together */
1452                                 tuple_fraction += limit_fraction;
1453                         }
1454                         else
1455                         {
1456                                 /* caller absolute, limit fractional; use limit */
1457                                 tuple_fraction = limit_fraction;
1458                         }
1459                 }
1460                 else
1461                 {
1462                         if (limit_fraction >= 1.0)
1463                         {
1464                                 /* caller fractional, limit absolute; use caller's value */
1465                         }
1466                         else
1467                         {
1468                                 /* both fractional, so add them together */
1469                                 tuple_fraction += limit_fraction;
1470                                 if (tuple_fraction >= 1.0)
1471                                         tuple_fraction = 0.0;           /* assume fetch all */
1472                         }
1473                 }
1474         }
1475
1476         return tuple_fraction;
1477 }
1478
1479 /*
1480  * extract_grouping_ops - make an array of the equality operator OIDs
1481  *              for the GROUP BY clause
1482  */
1483 static Oid *
1484 extract_grouping_ops(List *groupClause)
1485 {
1486         int                     numCols = list_length(groupClause);
1487         int                     colno = 0;
1488         Oid                *groupOperators;
1489         ListCell   *glitem;
1490
1491         groupOperators = (Oid *) palloc(sizeof(Oid) * numCols);
1492
1493         foreach(glitem, groupClause)
1494         {
1495                 GroupClause *groupcl = (GroupClause *) lfirst(glitem);
1496
1497                 groupOperators[colno] = get_equality_op_for_ordering_op(groupcl->sortop);
1498                 if (!OidIsValid(groupOperators[colno])) /* shouldn't happen */
1499                         elog(ERROR, "could not find equality operator for ordering operator %u",
1500                                  groupcl->sortop);
1501                 colno++;
1502         }
1503
1504         return groupOperators;
1505 }
1506
1507 /*
1508  * choose_hashed_grouping - should we use hashed grouping?
1509  */
1510 static bool
1511 choose_hashed_grouping(PlannerInfo *root,
1512                                            double tuple_fraction, double limit_tuples,
1513                                            Path *cheapest_path, Path *sorted_path,
1514                                            Oid *groupOperators, double dNumGroups,
1515                                            AggClauseCounts *agg_counts)
1516 {
1517         int                     numGroupCols = list_length(root->parse->groupClause);
1518         double          cheapest_path_rows;
1519         int                     cheapest_path_width;
1520         Size            hashentrysize;
1521         List       *current_pathkeys;
1522         Path            hashed_p;
1523         Path            sorted_p;
1524         int                     i;
1525
1526         /*
1527          * Check can't-do-it conditions, including whether the grouping operators
1528          * are hashjoinable.  (We assume hashing is OK if they are marked
1529          * oprcanhash.  If there isn't actually a supporting hash function, the
1530          * executor will complain at runtime.)
1531          *
1532          * Executor doesn't support hashed aggregation with DISTINCT aggregates.
1533          * (Doing so would imply storing *all* the input values in the hash table,
1534          * which seems like a certain loser.)
1535          */
1536         if (!enable_hashagg)
1537                 return false;
1538         if (agg_counts->numDistinctAggs != 0)
1539                 return false;
1540         for (i = 0; i < numGroupCols; i++)
1541         {
1542                 if (!op_hashjoinable(groupOperators[i]))
1543                         return false;
1544         }
1545
1546         /*
1547          * Don't do it if it doesn't look like the hashtable will fit into
1548          * work_mem.
1549          *
1550          * Beware here of the possibility that cheapest_path->parent is NULL. This
1551          * could happen if user does something silly like SELECT 'foo' GROUP BY 1;
1552          */
1553         if (cheapest_path->parent)
1554         {
1555                 cheapest_path_rows = cheapest_path->parent->rows;
1556                 cheapest_path_width = cheapest_path->parent->width;
1557         }
1558         else
1559         {
1560                 cheapest_path_rows = 1; /* assume non-set result */
1561                 cheapest_path_width = 100;              /* arbitrary */
1562         }
1563
1564         /* Estimate per-hash-entry space at tuple width... */
1565         hashentrysize = MAXALIGN(cheapest_path_width) + MAXALIGN(sizeof(MinimalTupleData));
1566         /* plus space for pass-by-ref transition values... */
1567         hashentrysize += agg_counts->transitionSpace;
1568         /* plus the per-hash-entry overhead */
1569         hashentrysize += hash_agg_entry_size(agg_counts->numAggs);
1570
1571         if (hashentrysize * dNumGroups > work_mem * 1024L)
1572                 return false;
1573
1574         /*
1575          * See if the estimated cost is no more than doing it the other way. While
1576          * avoiding the need for sorted input is usually a win, the fact that the
1577          * output won't be sorted may be a loss; so we need to do an actual cost
1578          * comparison.
1579          *
1580          * We need to consider cheapest_path + hashagg [+ final sort] versus
1581          * either cheapest_path [+ sort] + group or agg [+ final sort] or
1582          * presorted_path + group or agg [+ final sort] where brackets indicate a
1583          * step that may not be needed. We assume query_planner() will have
1584          * returned a presorted path only if it's a winner compared to
1585          * cheapest_path for this purpose.
1586          *
1587          * These path variables are dummies that just hold cost fields; we don't
1588          * make actual Paths for these steps.
1589          */
1590         cost_agg(&hashed_p, root, AGG_HASHED, agg_counts->numAggs,
1591                          numGroupCols, dNumGroups,
1592                          cheapest_path->startup_cost, cheapest_path->total_cost,
1593                          cheapest_path_rows);
1594         /* Result of hashed agg is always unsorted */
1595         if (root->sort_pathkeys)
1596                 cost_sort(&hashed_p, root, root->sort_pathkeys, hashed_p.total_cost,
1597                                   dNumGroups, cheapest_path_width, limit_tuples);
1598
1599         if (sorted_path)
1600         {
1601                 sorted_p.startup_cost = sorted_path->startup_cost;
1602                 sorted_p.total_cost = sorted_path->total_cost;
1603                 current_pathkeys = sorted_path->pathkeys;
1604         }
1605         else
1606         {
1607                 sorted_p.startup_cost = cheapest_path->startup_cost;
1608                 sorted_p.total_cost = cheapest_path->total_cost;
1609                 current_pathkeys = cheapest_path->pathkeys;
1610         }
1611         if (!pathkeys_contained_in(root->group_pathkeys, current_pathkeys))
1612         {
1613                 cost_sort(&sorted_p, root, root->group_pathkeys, sorted_p.total_cost,
1614                                   cheapest_path_rows, cheapest_path_width, -1.0);
1615                 current_pathkeys = root->group_pathkeys;
1616         }
1617
1618         if (root->parse->hasAggs)
1619                 cost_agg(&sorted_p, root, AGG_SORTED, agg_counts->numAggs,
1620                                  numGroupCols, dNumGroups,
1621                                  sorted_p.startup_cost, sorted_p.total_cost,
1622                                  cheapest_path_rows);
1623         else
1624                 cost_group(&sorted_p, root, numGroupCols, dNumGroups,
1625                                    sorted_p.startup_cost, sorted_p.total_cost,
1626                                    cheapest_path_rows);
1627         /* The Agg or Group node will preserve ordering */
1628         if (root->sort_pathkeys &&
1629                 !pathkeys_contained_in(root->sort_pathkeys, current_pathkeys))
1630                 cost_sort(&sorted_p, root, root->sort_pathkeys, sorted_p.total_cost,
1631                                   dNumGroups, cheapest_path_width, limit_tuples);
1632
1633         /*
1634          * Now make the decision using the top-level tuple fraction.  First we
1635          * have to convert an absolute count (LIMIT) into fractional form.
1636          */
1637         if (tuple_fraction >= 1.0)
1638                 tuple_fraction /= dNumGroups;
1639
1640         if (compare_fractional_path_costs(&hashed_p, &sorted_p,
1641                                                                           tuple_fraction) < 0)
1642         {
1643                 /* Hashed is cheaper, so use it */
1644                 return true;
1645         }
1646         return false;
1647 }
1648
1649 /*---------------
1650  * make_subplanTargetList
1651  *        Generate appropriate target list when grouping is required.
1652  *
1653  * When grouping_planner inserts Aggregate, Group, or Result plan nodes
1654  * above the result of query_planner, we typically want to pass a different
1655  * target list to query_planner than the outer plan nodes should have.
1656  * This routine generates the correct target list for the subplan.
1657  *
1658  * The initial target list passed from the parser already contains entries
1659  * for all ORDER BY and GROUP BY expressions, but it will not have entries
1660  * for variables used only in HAVING clauses; so we need to add those
1661  * variables to the subplan target list.  Also, we flatten all expressions
1662  * except GROUP BY items into their component variables; the other expressions
1663  * will be computed by the inserted nodes rather than by the subplan.
1664  * For example, given a query like
1665  *              SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
1666  * we want to pass this targetlist to the subplan:
1667  *              a,b,c,d,a+b
1668  * where the a+b target will be used by the Sort/Group steps, and the
1669  * other targets will be used for computing the final results.  (In the
1670  * above example we could theoretically suppress the a and b targets and
1671  * pass down only c,d,a+b, but it's not really worth the trouble to
1672  * eliminate simple var references from the subplan.  We will avoid doing
1673  * the extra computation to recompute a+b at the outer level; see
1674  * fix_upper_expr() in setrefs.c.)
1675  *
1676  * If we are grouping or aggregating, *and* there are no non-Var grouping
1677  * expressions, then the returned tlist is effectively dummy; we do not
1678  * need to force it to be evaluated, because all the Vars it contains
1679  * should be present in the output of query_planner anyway.
1680  *
1681  * 'tlist' is the query's target list.
1682  * 'groupColIdx' receives an array of column numbers for the GROUP BY
1683  *                      expressions (if there are any) in the subplan's target list.
1684  * 'need_tlist_eval' is set true if we really need to evaluate the
1685  *                      result tlist.
1686  *
1687  * The result is the targetlist to be passed to the subplan.
1688  *---------------
1689  */
1690 static List *
1691 make_subplanTargetList(PlannerInfo *root,
1692                                            List *tlist,
1693                                            AttrNumber **groupColIdx,
1694                                            bool *need_tlist_eval)
1695 {
1696         Query      *parse = root->parse;
1697         List       *sub_tlist;
1698         List       *extravars;
1699         int                     numCols;
1700
1701         *groupColIdx = NULL;
1702
1703         /*
1704          * If we're not grouping or aggregating, there's nothing to do here;
1705          * query_planner should receive the unmodified target list.
1706          */
1707         if (!parse->hasAggs && !parse->groupClause && !root->hasHavingQual)
1708         {
1709                 *need_tlist_eval = true;
1710                 return tlist;
1711         }
1712
1713         /*
1714          * Otherwise, start with a "flattened" tlist (having just the vars
1715          * mentioned in the targetlist and HAVING qual --- but not upper- level
1716          * Vars; they will be replaced by Params later on).
1717          */
1718         sub_tlist = flatten_tlist(tlist);
1719         extravars = pull_var_clause(parse->havingQual, false);
1720         sub_tlist = add_to_flat_tlist(sub_tlist, extravars);
1721         list_free(extravars);
1722         *need_tlist_eval = false;       /* only eval if not flat tlist */
1723
1724         /*
1725          * If grouping, create sub_tlist entries for all GROUP BY expressions
1726          * (GROUP BY items that are simple Vars should be in the list already),
1727          * and make an array showing where the group columns are in the sub_tlist.
1728          */
1729         numCols = list_length(parse->groupClause);
1730         if (numCols > 0)
1731         {
1732                 int                     keyno = 0;
1733                 AttrNumber *grpColIdx;
1734                 ListCell   *gl;
1735
1736                 grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols);
1737                 *groupColIdx = grpColIdx;
1738
1739                 foreach(gl, parse->groupClause)
1740                 {
1741                         GroupClause *grpcl = (GroupClause *) lfirst(gl);
1742                         Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1743                         TargetEntry *te = NULL;
1744                         ListCell   *sl;
1745
1746                         /* Find or make a matching sub_tlist entry */
1747                         foreach(sl, sub_tlist)
1748                         {
1749                                 te = (TargetEntry *) lfirst(sl);
1750                                 if (equal(groupexpr, te->expr))
1751                                         break;
1752                         }
1753                         if (!sl)
1754                         {
1755                                 te = makeTargetEntry((Expr *) groupexpr,
1756                                                                          list_length(sub_tlist) + 1,
1757                                                                          NULL,
1758                                                                          false);
1759                                 sub_tlist = lappend(sub_tlist, te);
1760                                 *need_tlist_eval = true;                /* it's not flat anymore */
1761                         }
1762
1763                         /* and save its resno */
1764                         grpColIdx[keyno++] = te->resno;
1765                 }
1766         }
1767
1768         return sub_tlist;
1769 }
1770
1771 /*
1772  * locate_grouping_columns
1773  *              Locate grouping columns in the tlist chosen by query_planner.
1774  *
1775  * This is only needed if we don't use the sub_tlist chosen by
1776  * make_subplanTargetList.      We have to forget the column indexes found
1777  * by that routine and re-locate the grouping vars in the real sub_tlist.
1778  */
1779 static void
1780 locate_grouping_columns(PlannerInfo *root,
1781                                                 List *tlist,
1782                                                 List *sub_tlist,
1783                                                 AttrNumber *groupColIdx)
1784 {
1785         int                     keyno = 0;
1786         ListCell   *gl;
1787
1788         /*
1789          * No work unless grouping.
1790          */
1791         if (!root->parse->groupClause)
1792         {
1793                 Assert(groupColIdx == NULL);
1794                 return;
1795         }
1796         Assert(groupColIdx != NULL);
1797
1798         foreach(gl, root->parse->groupClause)
1799         {
1800                 GroupClause *grpcl = (GroupClause *) lfirst(gl);
1801                 Node       *groupexpr = get_sortgroupclause_expr(grpcl, tlist);
1802                 TargetEntry *te = NULL;
1803                 ListCell   *sl;
1804
1805                 foreach(sl, sub_tlist)
1806                 {
1807                         te = (TargetEntry *) lfirst(sl);
1808                         if (equal(groupexpr, te->expr))
1809                                 break;
1810                 }
1811                 if (!sl)
1812                         elog(ERROR, "failed to locate grouping columns");
1813
1814                 groupColIdx[keyno++] = te->resno;
1815         }
1816 }
1817
1818 /*
1819  * postprocess_setop_tlist
1820  *        Fix up targetlist returned by plan_set_operations().
1821  *
1822  * We need to transpose sort key info from the orig_tlist into new_tlist.
1823  * NOTE: this would not be good enough if we supported resjunk sort keys
1824  * for results of set operations --- then, we'd need to project a whole
1825  * new tlist to evaluate the resjunk columns.  For now, just ereport if we
1826  * find any resjunk columns in orig_tlist.
1827  */
1828 static List *
1829 postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
1830 {
1831         ListCell   *l;
1832         ListCell   *orig_tlist_item = list_head(orig_tlist);
1833
1834         foreach(l, new_tlist)
1835         {
1836                 TargetEntry *new_tle = (TargetEntry *) lfirst(l);
1837                 TargetEntry *orig_tle;
1838
1839                 /* ignore resjunk columns in setop result */
1840                 if (new_tle->resjunk)
1841                         continue;
1842
1843                 Assert(orig_tlist_item != NULL);
1844                 orig_tle = (TargetEntry *) lfirst(orig_tlist_item);
1845                 orig_tlist_item = lnext(orig_tlist_item);
1846                 if (orig_tle->resjunk)  /* should not happen */
1847                         elog(ERROR, "resjunk output columns are not implemented");
1848                 Assert(new_tle->resno == orig_tle->resno);
1849                 new_tle->ressortgroupref = orig_tle->ressortgroupref;
1850         }
1851         if (orig_tlist_item != NULL)
1852                 elog(ERROR, "resjunk output columns are not implemented");
1853         return new_tlist;
1854 }