/*------------------------------------------------------------------------- * * planner.c * The query optimizer external interface. * * Portions Copyright (c) 1996-2000, PostgreSQL, Inc * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.98 2000/12/14 22:30:43 tgl Exp $ * *------------------------------------------------------------------------- */ #include "postgres.h" #include "catalog/pg_type.h" #include "nodes/makefuncs.h" #include "optimizer/clauses.h" #include "optimizer/paths.h" #include "optimizer/planmain.h" #include "optimizer/planner.h" #include "optimizer/prep.h" #include "optimizer/subselect.h" #include "optimizer/tlist.h" #include "optimizer/var.h" #include "parser/analyze.h" #include "parser/parsetree.h" #include "parser/parse_expr.h" #include "rewrite/rewriteManip.h" #include "utils/lsyscache.h" /* Expression kind codes for preprocess_expression */ #define EXPRKIND_TARGET 0 #define EXPRKIND_WHERE 1 #define EXPRKIND_HAVING 2 static Node *pull_up_subqueries(Query *parse, Node *jtnode); static bool is_simple_subquery(Query *subquery); static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist); static Node *preprocess_jointree(Query *parse, Node *jtnode); static Node *preprocess_expression(Query *parse, Node *expr, int kind); static void preprocess_qual_conditions(Query *parse, Node *jtnode); static Plan *inheritance_planner(Query *parse, List *inheritlist); static Plan *grouping_planner(Query *parse, double tuple_fraction); static List *make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx); static Plan *make_groupplan(List *group_tlist, bool tuplePerGroup, List *groupClause, AttrNumber *grpColIdx, bool is_presorted, Plan *subplan); static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist); /***************************************************************************** * * Query optimizer entry point * *****************************************************************************/ Plan * planner(Query *parse) { Plan *result_plan; Index save_PlannerQueryLevel; List *save_PlannerParamVar; /* * The planner can be called recursively (an example is when * eval_const_expressions tries to pre-evaluate an SQL function). * So, these global state variables must be saved and restored. * * These vars cannot be moved into the Query structure since their * whole purpose is communication across multiple sub-Queries. * * Note we do NOT save and restore PlannerPlanId: it exists to assign * unique IDs to SubPlan nodes, and we want those IDs to be unique * for the life of a backend. Also, PlannerInitPlan is saved/restored * in subquery_planner, not here. */ save_PlannerQueryLevel = PlannerQueryLevel; save_PlannerParamVar = PlannerParamVar; /* Initialize state for handling outer-level references and params */ PlannerQueryLevel = 0; /* will be 1 in top-level subquery_planner */ PlannerParamVar = NIL; /* primary planning entry point (may recurse for subqueries) */ result_plan = subquery_planner(parse, -1.0 /* default case */ ); Assert(PlannerQueryLevel == 0); /* executor wants to know total number of Params used overall */ result_plan->nParamExec = length(PlannerParamVar); /* final cleanup of the plan */ set_plan_references(result_plan); /* restore state for outer planner, if any */ PlannerQueryLevel = save_PlannerQueryLevel; PlannerParamVar = save_PlannerParamVar; return result_plan; } /*-------------------- * subquery_planner * Invokes the planner on a subquery. We recurse to here for each * sub-SELECT found in the query tree. * * parse is the querytree produced by the parser & rewriter. * tuple_fraction is the fraction of tuples we expect will be retrieved. * tuple_fraction is interpreted as explained for grouping_planner, below. * * Basically, this routine does the stuff that should only be done once * per Query object. It then calls grouping_planner. At one time, * grouping_planner could be invoked recursively on the same Query object; * that's not currently true, but we keep the separation between the two * routines anyway, in case we need it again someday. * * subquery_planner will be called recursively to handle sub-Query nodes * found within the query's expressions and rangetable. * * Returns a query plan. *-------------------- */ Plan * subquery_planner(Query *parse, double tuple_fraction) { List *saved_initplan = PlannerInitPlan; int saved_planid = PlannerPlanId; Plan *plan; List *lst; /* Set up for a new level of subquery */ PlannerQueryLevel++; PlannerInitPlan = NIL; #ifdef ENABLE_KEY_SET_QUERY /* this should go away sometime soon */ transformKeySetQuery(parse); #endif /* * Check to see if any subqueries in the rangetable can be merged into * this query. */ parse->jointree = (FromExpr *) pull_up_subqueries(parse, (Node *) parse->jointree); /* * If so, we may have created opportunities to simplify the jointree. */ parse->jointree = (FromExpr *) preprocess_jointree(parse, (Node *) parse->jointree); /* * A HAVING clause without aggregates is equivalent to a WHERE clause * (except it can only refer to grouped fields). If there are no aggs * anywhere in the query, then we don't want to create an Agg plan * node, so merge the HAVING condition into WHERE. (We used to * consider this an error condition, but it seems to be legal SQL.) */ if (parse->havingQual != NULL && !parse->hasAggs) { parse->jointree->quals = make_and_qual(parse->jointree->quals, parse->havingQual); parse->havingQual = NULL; } /* * Do expression preprocessing on targetlist and quals. */ parse->targetList = (List *) preprocess_expression(parse, (Node *) parse->targetList, EXPRKIND_TARGET); preprocess_qual_conditions(parse, (Node *) parse->jointree); parse->havingQual = preprocess_expression(parse, parse->havingQual, EXPRKIND_HAVING); /* * Do the main planning. If we have an inherited target relation, * that needs special processing, else go straight to grouping_planner. */ if (parse->resultRelation && (lst = expand_inherted_rtentry(parse, parse->resultRelation)) != NIL) plan = inheritance_planner(parse, lst); else plan = grouping_planner(parse, tuple_fraction); /* * If any subplans were generated, or if we're inside a subplan, * build subPlan, extParam and locParam lists for plan nodes. */ if (PlannerPlanId != saved_planid || PlannerQueryLevel > 1) { (void) SS_finalize_plan(plan); /* * At the moment, SS_finalize_plan doesn't handle initPlans * and so we assign them to the topmost plan node. */ plan->initPlan = PlannerInitPlan; /* Must add the initPlans' extParams to the topmost node's, too */ foreach(lst, plan->initPlan) { SubPlan *subplan = (SubPlan *) lfirst(lst); plan->extParam = set_unioni(plan->extParam, subplan->plan->extParam); } } /* Return to outer subquery context */ PlannerQueryLevel--; PlannerInitPlan = saved_initplan; /* we do NOT restore PlannerPlanId; that's not an oversight! */ return plan; } /* * pull_up_subqueries * Look for subqueries in the rangetable that can be pulled up into * the parent query. If the subquery has no special features like * grouping/aggregation then we can merge it into the parent's jointree. * * A tricky aspect of this code is that if we pull up a subquery we have * to replace Vars that reference the subquery's outputs throughout the * parent query, including quals attached to jointree nodes above the one * we are currently processing! We handle this by being careful not to * change the jointree structure while recursing: no nodes other than * subquery RangeTblRef entries will be replaced. Also, we can't turn * ResolveNew loose on the whole jointree, because it'll return a mutated * copy of the tree; we have to invoke it just on the quals, instead. */ static Node * pull_up_subqueries(Query *parse, Node *jtnode) { if (jtnode == NULL) return NULL; if (IsA(jtnode, RangeTblRef)) { int varno = ((RangeTblRef *) jtnode)->rtindex; RangeTblEntry *rte = rt_fetch(varno, parse->rtable); Query *subquery = rte->subquery; /* * Is this a subquery RTE, and if so, is the subquery simple enough * to pull up? (If not, do nothing at this node.) */ if (subquery && is_simple_subquery(subquery)) { int rtoffset; Node *subjointree; List *subtlist; List *l; /* * First, recursively pull up the subquery's subqueries, * so that this routine's processing is complete for its * jointree and rangetable. */ subquery->jointree = (FromExpr *) pull_up_subqueries(subquery, (Node *) subquery->jointree); /* * Append the subquery's rangetable to mine (currently, * no adjustments will be needed in the subquery's rtable). */ rtoffset = length(parse->rtable); parse->rtable = nconc(parse->rtable, subquery->rtable); /* * Make copies of the subquery's jointree and targetlist * with varnos adjusted to match the merged rangetable. */ subjointree = copyObject(subquery->jointree); OffsetVarNodes(subjointree, rtoffset, 0); subtlist = copyObject(subquery->targetList); OffsetVarNodes((Node *) subtlist, rtoffset, 0); /* * Replace all of the top query's references to the subquery's * outputs with copies of the adjusted subtlist items, being * careful not to replace any of the jointree structure. */ parse->targetList = (List *) ResolveNew((Node *) parse->targetList, varno, 0, subtlist, CMD_SELECT, 0); resolvenew_in_jointree((Node *) parse->jointree, varno, subtlist); parse->havingQual = ResolveNew(parse->havingQual, varno, 0, subtlist, CMD_SELECT, 0); /* * Pull up any FOR UPDATE markers, too. */ foreach(l, subquery->rowMarks) { int submark = lfirsti(l); parse->rowMarks = lappendi(parse->rowMarks, submark + rtoffset); } /* * Miscellaneous housekeeping. */ parse->hasSubLinks |= subquery->hasSubLinks; /* subquery won't be pulled up if it hasAggs, so no work there */ /* * Return the adjusted subquery jointree to replace the * RangeTblRef entry in my jointree. */ return subjointree; } } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *l; foreach(l, f->fromlist) { lfirst(l) = pull_up_subqueries(parse, lfirst(l)); } } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; j->larg = pull_up_subqueries(parse, j->larg); j->rarg = pull_up_subqueries(parse, j->rarg); } else elog(ERROR, "pull_up_subqueries: unexpected node type %d", nodeTag(jtnode)); return jtnode; } /* * is_simple_subquery * Check a subquery in the range table to see if it's simple enough * to pull up into the parent query. */ static bool is_simple_subquery(Query *subquery) { /* * Let's just make sure it's a valid subselect ... */ if (!IsA(subquery, Query) || subquery->commandType != CMD_SELECT || subquery->resultRelation != 0 || subquery->into != NULL || subquery->isPortal) elog(ERROR, "is_simple_subquery: subquery is bogus"); /* * Can't currently pull up a query with setops. * Maybe after querytree redesign... */ if (subquery->setOperations) return false; /* * Can't pull up a subquery involving grouping, aggregation, sorting, * or limiting. */ if (subquery->hasAggs || subquery->groupClause || subquery->havingQual || subquery->sortClause || subquery->distinctClause || subquery->limitOffset || subquery->limitCount) return false; /* * Hack: don't try to pull up a subquery with an empty jointree. * query_planner() will correctly generate a Result plan for a * jointree that's totally empty, but I don't think the right things * happen if an empty FromExpr appears lower down in a jointree. * Not worth working hard on this, just to collapse SubqueryScan/Result * into Result... */ if (subquery->jointree->fromlist == NIL) return false; return true; } /* * Helper routine for pull_up_subqueries: do ResolveNew on every expression * in the jointree, without changing the jointree structure itself. Ugly, * but there's no other way... */ static void resolvenew_in_jointree(Node *jtnode, int varno, List *subtlist) { if (jtnode == NULL) return; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *l; foreach(l, f->fromlist) resolvenew_in_jointree(lfirst(l), varno, subtlist); f->quals = ResolveNew(f->quals, varno, 0, subtlist, CMD_SELECT, 0); } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; resolvenew_in_jointree(j->larg, varno, subtlist); resolvenew_in_jointree(j->rarg, varno, subtlist); j->quals = ResolveNew(j->quals, varno, 0, subtlist, CMD_SELECT, 0); /* We don't bother to update the colvars list, since it won't be * used again ... */ } else elog(ERROR, "resolvenew_in_jointree: unexpected node type %d", nodeTag(jtnode)); } /* * preprocess_jointree * Attempt to simplify a query's jointree. * * If we succeed in pulling up a subquery then we might form a jointree * in which a FromExpr is a direct child of another FromExpr. In that * case we can consider collapsing the two FromExprs into one. This is * an optional conversion, since the planner will work correctly either * way. But we may find a better plan (at the cost of more planning time) * if we merge the two nodes. * * NOTE: don't try to do this in the same jointree scan that does subquery * pullup! Since we're changing the jointree structure here, that wouldn't * work reliably --- see comments for pull_up_subqueries(). */ static Node * preprocess_jointree(Query *parse, Node *jtnode) { if (jtnode == NULL) return NULL; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here... */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *newlist = NIL; List *l; foreach(l, f->fromlist) { Node *child = (Node *) lfirst(l); /* Recursively simplify the child... */ child = preprocess_jointree(parse, child); /* Now, is it a FromExpr? */ if (child && IsA(child, FromExpr)) { /* * Yes, so do we want to merge it into parent? Always do so * if child has just one element (since that doesn't make the * parent's list any longer). Otherwise we have to be careful * about the increase in planning time caused by combining the * two join search spaces into one. Our heuristic is to merge * if the merge will produce a join list no longer than * GEQO_RELS/2. (Perhaps need an additional user parameter?) */ FromExpr *subf = (FromExpr *) child; int childlen = length(subf->fromlist); int myothers = length(newlist) + length(lnext(l)); if (childlen <= 1 || (childlen+myothers) <= geqo_rels/2) { newlist = nconc(newlist, subf->fromlist); f->quals = make_and_qual(f->quals, subf->quals); } else newlist = lappend(newlist, child); } else newlist = lappend(newlist, child); } f->fromlist = newlist; } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; /* Can't usefully change the JoinExpr, but recurse on children */ j->larg = preprocess_jointree(parse, j->larg); j->rarg = preprocess_jointree(parse, j->rarg); } else elog(ERROR, "preprocess_jointree: unexpected node type %d", nodeTag(jtnode)); return jtnode; } /* * preprocess_expression * Do subquery_planner's preprocessing work for an expression, * which can be a targetlist, a WHERE clause (including JOIN/ON * conditions), or a HAVING clause. */ static Node * preprocess_expression(Query *parse, Node *expr, int kind) { /* * Simplify constant expressions. * * Note that at this point quals have not yet been converted to * implicit-AND form, so we can apply eval_const_expressions directly. * Also note that we need to do this before SS_process_sublinks, * because that routine inserts bogus "Const" nodes. */ expr = eval_const_expressions(expr); /* * If it's a qual or havingQual, canonicalize it, and convert it * to implicit-AND format. * * XXX Is there any value in re-applying eval_const_expressions after * canonicalize_qual? */ if (kind != EXPRKIND_TARGET) { expr = (Node *) canonicalize_qual((Expr *) expr, true); #ifdef OPTIMIZER_DEBUG printf("After canonicalize_qual()\n"); pprint(expr); #endif } if (parse->hasSubLinks) { /* Expand SubLinks to SubPlans */ expr = SS_process_sublinks(expr); if (kind != EXPRKIND_WHERE && (parse->groupClause != NIL || parse->hasAggs)) { /* * Check for ungrouped variables passed to subplans. Note we * do NOT do this for subplans in WHERE (or JOIN/ON); it's legal * there because WHERE is evaluated pre-GROUP. * * An interesting fine point: if subquery_planner reassigned a * HAVING qual into WHERE, then we will accept references to * ungrouped vars from subplans in the HAVING qual. This is not * entirely consistent, but it doesn't seem particularly * harmful... */ check_subplans_for_ungrouped_vars(expr, parse); } } /* Replace uplevel vars with Param nodes */ if (PlannerQueryLevel > 1) expr = SS_replace_correlation_vars(expr); return expr; } /* * preprocess_qual_conditions * Recursively scan the query's jointree and do subquery_planner's * preprocessing work on each qual condition found therein. */ static void preprocess_qual_conditions(Query *parse, Node *jtnode) { if (jtnode == NULL) return; if (IsA(jtnode, RangeTblRef)) { /* nothing to do here */ } else if (IsA(jtnode, FromExpr)) { FromExpr *f = (FromExpr *) jtnode; List *l; foreach(l, f->fromlist) preprocess_qual_conditions(parse, lfirst(l)); f->quals = preprocess_expression(parse, f->quals, EXPRKIND_WHERE); } else if (IsA(jtnode, JoinExpr)) { JoinExpr *j = (JoinExpr *) jtnode; preprocess_qual_conditions(parse, j->larg); preprocess_qual_conditions(parse, j->rarg); j->quals = preprocess_expression(parse, j->quals, EXPRKIND_WHERE); } else elog(ERROR, "preprocess_qual_conditions: unexpected node type %d", nodeTag(jtnode)); } /*-------------------- * inheritance_planner * Generate a plan in the case where the result relation is an * inheritance set. * * We have to handle this case differently from cases where a source * relation is an inheritance set. Source inheritance is expanded at * the bottom of the plan tree (see allpaths.c), but target inheritance * has to be expanded at the top. The reason is that for UPDATE, each * target relation needs a different targetlist matching its own column * set. (This is not so critical for DELETE, but for simplicity we treat * inherited DELETE the same way.) Fortunately, the UPDATE/DELETE target * can never be the nullable side of an outer join, so it's OK to generate * the plan this way. * * parse is the querytree produced by the parser & rewriter. * inheritlist is an integer list of RT indexes for the result relation set. * * Returns a query plan. *-------------------- */ static Plan * inheritance_planner(Query *parse, List *inheritlist) { int parentRTindex = parse->resultRelation; Oid parentOID = getrelid(parentRTindex, parse->rtable); List *subplans = NIL; List *tlist = NIL; List *l; foreach(l, inheritlist) { int childRTindex = lfirsti(l); Oid childOID = getrelid(childRTindex, parse->rtable); Query *subquery; Plan *subplan; /* Generate modified query with this rel as target */ subquery = (Query *) adjust_inherited_attrs((Node *) parse, parentRTindex, parentOID, childRTindex, childOID); /* Generate plan */ subplan = grouping_planner(subquery, 0.0 /* retrieve all tuples */); subplans = lappend(subplans, subplan); /* Save preprocessed tlist from first rel for use in Append */ if (tlist == NIL) tlist = subplan->targetlist; } /* Save the target-relations list for the executor, too */ parse->resultRelations = inheritlist; return (Plan *) make_append(subplans, true, tlist); } /*-------------------- * grouping_planner * Perform planning steps related to grouping, aggregation, etc. * This primarily means adding top-level processing to the basic * query plan produced by query_planner. * * parse is the querytree produced by the parser & rewriter. * tuple_fraction is the fraction of tuples we expect will be retrieved * * tuple_fraction is interpreted as follows: * < 0: determine fraction by inspection of query (normal case) * 0: expect all tuples to be retrieved * 0 < tuple_fraction < 1: expect the given fraction of tuples available * from the plan to be retrieved * tuple_fraction >= 1: tuple_fraction is the absolute number of tuples * expected to be retrieved (ie, a LIMIT specification) * The normal case is to pass -1, but some callers pass values >= 0 to * override this routine's determination of the appropriate fraction. * * Returns a query plan. *-------------------- */ static Plan * grouping_planner(Query *parse, double tuple_fraction) { List *tlist = parse->targetList; Plan *result_plan; List *current_pathkeys; List *group_pathkeys; List *sort_pathkeys; AttrNumber *groupColIdx = NULL; if (parse->setOperations) { /* * Construct the plan for set operations. The result will not * need any work except perhaps a top-level sort and/or LIMIT. */ result_plan = plan_set_operations(parse); /* * We should not need to call preprocess_targetlist, since we must * be in a SELECT query node. Instead, use the targetlist * returned by plan_set_operations (since this tells whether it * returned any resjunk columns!), and transfer any sort key * information from the original tlist. */ Assert(parse->commandType == CMD_SELECT); tlist = postprocess_setop_tlist(result_plan->targetlist, tlist); /* * Can't handle FOR UPDATE here (parser should have checked already, * but let's make sure). */ if (parse->rowMarks) elog(ERROR, "SELECT FOR UPDATE is not allowed with UNION/INTERSECT/EXCEPT"); /* * We set current_pathkeys NIL indicating we do not know sort * order. This is correct when the top set operation is UNION ALL, * since the appended-together results are unsorted even if the * subplans were sorted. For other set operations we could be * smarter --- room for future improvement! */ current_pathkeys = NIL; /* * Calculate pathkeys that represent grouping/ordering * requirements (grouping should always be null, but...) */ group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause, tlist); sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause, tlist); } else { List *sub_tlist; /* Preprocess targetlist in case we are inside an INSERT/UPDATE. */ tlist = preprocess_targetlist(tlist, parse->commandType, parse->resultRelation, parse->rtable); /* * Add TID targets for rels selected FOR UPDATE (should this be * done in preprocess_targetlist?). The executor uses the TID * to know which rows to lock, much as for UPDATE or DELETE. */ if (parse->rowMarks) { List *l; /* * We've got trouble if the FOR UPDATE appears inside grouping, * since grouping renders a reference to individual tuple CTIDs * invalid. This is also checked at parse time, but that's * insufficient because of rule substitution, query pullup, etc. */ CheckSelectForUpdate(parse); /* Currently the executor only supports FOR UPDATE at top level */ if (PlannerQueryLevel > 1) elog(ERROR, "SELECT FOR UPDATE is not allowed in subselects"); foreach(l, parse->rowMarks) { Index rti = lfirsti(l); char *resname; Resdom *resdom; Var *var; TargetEntry *ctid; resname = (char *) palloc(32); sprintf(resname, "ctid%u", rti); resdom = makeResdom(length(tlist) + 1, TIDOID, -1, resname, true); var = makeVar(rti, SelfItemPointerAttributeNumber, TIDOID, -1, 0); ctid = makeTargetEntry(resdom, (Node *) var); tlist = lappend(tlist, ctid); } } /* * Generate appropriate target list for subplan; may be different * from tlist if grouping or aggregation is needed. */ sub_tlist = make_subplanTargetList(parse, tlist, &groupColIdx); /* * Calculate pathkeys that represent grouping/ordering * requirements */ group_pathkeys = make_pathkeys_for_sortclauses(parse->groupClause, tlist); sort_pathkeys = make_pathkeys_for_sortclauses(parse->sortClause, tlist); /* * Figure out whether we need a sorted result from query_planner. * * If we have a GROUP BY clause, then we want a result sorted * properly for grouping. Otherwise, if there is an ORDER BY * clause, we want to sort by the ORDER BY clause. (Note: if we * have both, and ORDER BY is a superset of GROUP BY, it would be * tempting to request sort by ORDER BY --- but that might just * leave us failing to exploit an available sort order at all. * Needs more thought...) */ if (parse->groupClause) parse->query_pathkeys = group_pathkeys; else if (parse->sortClause) parse->query_pathkeys = sort_pathkeys; else parse->query_pathkeys = NIL; /* * Figure out whether we expect to retrieve all the tuples that * the plan can generate, or to stop early due to a LIMIT or other * factors. If the caller passed a value >= 0, believe that * value, else do our own examination of the query context. */ if (tuple_fraction < 0.0) { /* Initial assumption is we need all the tuples */ tuple_fraction = 0.0; /* * Check for a LIMIT clause. */ if (parse->limitCount != NULL) { if (IsA(parse->limitCount, Const)) { Const *limitc = (Const *) parse->limitCount; int32 count = DatumGetInt32(limitc->constvalue); /* * A NULL-constant LIMIT represents "LIMIT ALL", * which we treat the same as no limit (ie, * expect to retrieve all the tuples). */ if (!limitc->constisnull && count > 0) { tuple_fraction = (double) count; /* We must also consider the OFFSET, if present */ if (parse->limitOffset != NULL) { if (IsA(parse->limitOffset, Const)) { int32 offset; limitc = (Const *) parse->limitOffset; offset = DatumGetInt32(limitc->constvalue); if (!limitc->constisnull && offset > 0) tuple_fraction += (double) offset; } else { /* It's an expression ... punt ... */ tuple_fraction = 0.10; } } } } else { /* * COUNT is an expression ... don't know exactly what the * limit will be, but for lack of a better idea assume * 10% of the plan's result is wanted. */ tuple_fraction = 0.10; } } /* * If no LIMIT, check for retrieve-into-portal, ie DECLARE CURSOR. * * We have no real idea how many tuples the user will ultimately * FETCH from a cursor, but it seems a good bet that he * doesn't want 'em all. Optimize for 10% retrieval (you * gotta better number?) */ else if (parse->isPortal) tuple_fraction = 0.10; } /* * Adjust tuple_fraction if we see that we are going to apply * grouping/aggregation/etc. This is not overridable by the * caller, since it reflects plan actions that this routine will * certainly take, not assumptions about context. */ if (parse->groupClause) { /* * In GROUP BY mode, we have the little problem that we don't * really know how many input tuples will be needed to make a * group, so we can't translate an output LIMIT count into an * input count. For lack of a better idea, assume 25% of the * input data will be processed if there is any output limit. * However, if the caller gave us a fraction rather than an * absolute count, we can keep using that fraction (which * amounts to assuming that all the groups are about the same * size). */ if (tuple_fraction >= 1.0) tuple_fraction = 0.25; /* * If both GROUP BY and ORDER BY are specified, we will need * two levels of sort --- and, therefore, certainly need to * read all the input tuples --- unless ORDER BY is a subset * of GROUP BY. (We have not yet canonicalized the pathkeys, * so must use the slower noncanonical comparison method.) */ if (parse->groupClause && parse->sortClause && !noncanonical_pathkeys_contained_in(sort_pathkeys, group_pathkeys)) tuple_fraction = 0.0; } else if (parse->hasAggs) { /* * Ungrouped aggregate will certainly want all the input * tuples. */ tuple_fraction = 0.0; } else if (parse->distinctClause) { /* * SELECT DISTINCT, like GROUP, will absorb an unpredictable * number of input tuples per output tuple. Handle the same * way. */ if (tuple_fraction >= 1.0) tuple_fraction = 0.25; } /* Generate the basic plan for this Query */ result_plan = query_planner(parse, sub_tlist, tuple_fraction); /* * query_planner returns actual sort order (which is not * necessarily what we requested) in query_pathkeys. */ current_pathkeys = parse->query_pathkeys; } /* * We couldn't canonicalize group_pathkeys and sort_pathkeys before * running query_planner(), so do it now. */ group_pathkeys = canonicalize_pathkeys(parse, group_pathkeys); sort_pathkeys = canonicalize_pathkeys(parse, sort_pathkeys); /* * If we have a GROUP BY clause, insert a group node (plus the * appropriate sort node, if necessary). */ if (parse->groupClause) { bool tuplePerGroup; List *group_tlist; bool is_sorted; /* * Decide whether how many tuples per group the Group node needs * to return. (Needs only one tuple per group if no aggregate is * present. Otherwise, need every tuple from the group to do the * aggregation.) Note tuplePerGroup is named backwards :-( */ tuplePerGroup = parse->hasAggs; /* * If there are aggregates then the Group node should just return * the same set of vars as the subplan did (but we can exclude any * GROUP BY expressions). If there are no aggregates then the * Group node had better compute the final tlist. */ if (parse->hasAggs) group_tlist = flatten_tlist(result_plan->targetlist); else group_tlist = tlist; /* * Figure out whether the path result is already ordered the way * we need it --- if so, no need for an explicit sort step. */ if (pathkeys_contained_in(group_pathkeys, current_pathkeys)) { is_sorted = true; /* no sort needed now */ /* current_pathkeys remains unchanged */ } else { /* * We will need to do an explicit sort by the GROUP BY clause. * make_groupplan will do the work, but set current_pathkeys * to indicate the resulting order. */ is_sorted = false; current_pathkeys = group_pathkeys; } result_plan = make_groupplan(group_tlist, tuplePerGroup, parse->groupClause, groupColIdx, is_sorted, result_plan); } /* * If aggregate is present, insert the Agg node * * HAVING clause, if any, becomes qual of the Agg node */ if (parse->hasAggs) { result_plan = (Plan *) make_agg(tlist, (List *) parse->havingQual, result_plan); /* Note: Agg does not affect any existing sort order of the tuples */ } /* * If we were not able to make the plan come out in the right order, * add an explicit sort step. */ if (parse->sortClause) { if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys)) result_plan = make_sortplan(tlist, result_plan, parse->sortClause); } /* * If there is a DISTINCT clause, add the UNIQUE node. */ if (parse->distinctClause) { result_plan = (Plan *) make_unique(tlist, result_plan, parse->distinctClause); } /* * Finally, if there is a LIMIT/OFFSET clause, add the LIMIT node. */ if (parse->limitOffset || parse->limitCount) { result_plan = (Plan *) make_limit(tlist, result_plan, parse->limitOffset, parse->limitCount); } return result_plan; } /*--------------- * make_subplanTargetList * Generate appropriate target list when grouping is required. * * When grouping_planner inserts Aggregate and/or Group plan nodes above * the result of query_planner, we typically want to pass a different * target list to query_planner than the outer plan nodes should have. * This routine generates the correct target list for the subplan. * * The initial target list passed from the parser already contains entries * for all ORDER BY and GROUP BY expressions, but it will not have entries * for variables used only in HAVING clauses; so we need to add those * variables to the subplan target list. Also, if we are doing either * grouping or aggregation, we flatten all expressions except GROUP BY items * into their component variables; the other expressions will be computed by * the inserted nodes rather than by the subplan. For example, * given a query like * SELECT a+b,SUM(c+d) FROM table GROUP BY a+b; * we want to pass this targetlist to the subplan: * a,b,c,d,a+b * where the a+b target will be used by the Sort/Group steps, and the * other targets will be used for computing the final results. (In the * above example we could theoretically suppress the a and b targets and * use only a+b, but it's not really worth the trouble.) * * 'parse' is the query being processed. * 'tlist' is the query's target list. * 'groupColIdx' receives an array of column numbers for the GROUP BY * expressions (if there are any) in the subplan's target list. * * The result is the targetlist to be passed to the subplan. *--------------- */ static List * make_subplanTargetList(Query *parse, List *tlist, AttrNumber **groupColIdx) { List *sub_tlist; List *extravars; int numCols; *groupColIdx = NULL; /* * If we're not grouping or aggregating, nothing to do here; * query_planner should receive the unmodified target list. */ if (!parse->hasAggs && !parse->groupClause && !parse->havingQual) return tlist; /* * Otherwise, start with a "flattened" tlist (having just the vars * mentioned in the targetlist and HAVING qual --- but not upper- * level Vars; they will be replaced by Params later on). */ sub_tlist = flatten_tlist(tlist); extravars = pull_var_clause(parse->havingQual, false); sub_tlist = add_to_flat_tlist(sub_tlist, extravars); freeList(extravars); /* * If grouping, create sub_tlist entries for all GROUP BY expressions * (GROUP BY items that are simple Vars should be in the list * already), and make an array showing where the group columns are in * the sub_tlist. */ numCols = length(parse->groupClause); if (numCols > 0) { int keyno = 0; AttrNumber *grpColIdx; List *gl; grpColIdx = (AttrNumber *) palloc(sizeof(AttrNumber) * numCols); *groupColIdx = grpColIdx; foreach(gl, parse->groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); Node *groupexpr = get_sortgroupclause_expr(grpcl, tlist); TargetEntry *te = NULL; List *sl; /* Find or make a matching sub_tlist entry */ foreach(sl, sub_tlist) { te = (TargetEntry *) lfirst(sl); if (equal(groupexpr, te->expr)) break; } if (!sl) { te = makeTargetEntry(makeResdom(length(sub_tlist) + 1, exprType(groupexpr), exprTypmod(groupexpr), NULL, false), groupexpr); sub_tlist = lappend(sub_tlist, te); } /* and save its resno */ grpColIdx[keyno++] = te->resdom->resno; } } return sub_tlist; } /* * make_groupplan * Add a Group node for GROUP BY processing. * If we couldn't make the subplan produce presorted output for grouping, * first add an explicit Sort node. */ static Plan * make_groupplan(List *group_tlist, bool tuplePerGroup, List *groupClause, AttrNumber *grpColIdx, bool is_presorted, Plan *subplan) { int numCols = length(groupClause); if (!is_presorted) { /* * The Sort node always just takes a copy of the subplan's tlist * plus ordering information. (This might seem inefficient if the * subplan contains complex GROUP BY expressions, but in fact Sort * does not evaluate its targetlist --- it only outputs the same * tuples in a new order. So the expressions we might be copying * are just dummies with no extra execution cost.) */ List *sort_tlist = new_unsorted_tlist(subplan->targetlist); int keyno = 0; List *gl; foreach(gl, groupClause) { GroupClause *grpcl = (GroupClause *) lfirst(gl); TargetEntry *te = nth(grpColIdx[keyno] - 1, sort_tlist); Resdom *resdom = te->resdom; /* * Check for the possibility of duplicate group-by clauses --- * the parser should have removed 'em, but the Sort executor * will get terribly confused if any get through! */ if (resdom->reskey == 0) { /* OK, insert the ordering info needed by the executor. */ resdom->reskey = ++keyno; resdom->reskeyop = get_opcode(grpcl->sortop); } } Assert(keyno > 0); subplan = (Plan *) make_sort(sort_tlist, subplan, keyno); } return (Plan *) make_group(group_tlist, tuplePerGroup, numCols, grpColIdx, subplan); } /* * make_sortplan * Add a Sort node to implement an explicit ORDER BY clause. */ Plan * make_sortplan(List *tlist, Plan *plannode, List *sortcls) { List *sort_tlist; List *i; int keyno = 0; /* * First make a copy of the tlist so that we don't corrupt the * original. */ sort_tlist = new_unsorted_tlist(tlist); foreach(i, sortcls) { SortClause *sortcl = (SortClause *) lfirst(i); TargetEntry *tle = get_sortgroupclause_tle(sortcl, sort_tlist); Resdom *resdom = tle->resdom; /* * Check for the possibility of duplicate order-by clauses --- the * parser should have removed 'em, but the executor will get * terribly confused if any get through! */ if (resdom->reskey == 0) { /* OK, insert the ordering info needed by the executor. */ resdom->reskey = ++keyno; resdom->reskeyop = get_opcode(sortcl->sortop); } } Assert(keyno > 0); return (Plan *) make_sort(sort_tlist, plannode, keyno); } /* * postprocess_setop_tlist * Fix up targetlist returned by plan_set_operations(). * * We need to transpose sort key info from the orig_tlist into new_tlist. * NOTE: this would not be good enough if we supported resjunk sort keys * for results of set operations --- then, we'd need to project a whole * new tlist to evaluate the resjunk columns. For now, just elog if we * find any resjunk columns in orig_tlist. */ static List * postprocess_setop_tlist(List *new_tlist, List *orig_tlist) { List *l; foreach(l, new_tlist) { TargetEntry *new_tle = (TargetEntry *) lfirst(l); TargetEntry *orig_tle; /* ignore resjunk columns in setop result */ if (new_tle->resdom->resjunk) continue; Assert(orig_tlist != NIL); orig_tle = (TargetEntry *) lfirst(orig_tlist); orig_tlist = lnext(orig_tlist); if (orig_tle->resdom->resjunk) elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented"); Assert(new_tle->resdom->resno == orig_tle->resdom->resno); Assert(new_tle->resdom->restype == orig_tle->resdom->restype); new_tle->resdom->ressortgroupref = orig_tle->resdom->ressortgroupref; } if (orig_tlist != NIL) elog(ERROR, "postprocess_setop_tlist: resjunk output columns not implemented"); return new_tlist; }