From: Tom Lane Date: Tue, 31 Jul 2001 18:39:13 +0000 (+0000) Subject: Fix optimizer to not try to push WHERE clauses down into a sub-SELECT that X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=658809c80a156bb5aca156aca70b7ba93e2bae5b;p=users%2Fbernd%2Fpostgres.git Fix optimizer to not try to push WHERE clauses down into a sub-SELECT that has a DISTINCT ON clause, per bug report from Anthony Wood. While at it, improve the DISTINCT-ON-clause recognizer routine to not be fooled by out- of-order DISTINCT lists. Also, back-patch earlier fix to not push down into sub-SELECT with LIMIT. --- diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index cb1ea631fa..a47a16b393 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -125,11 +125,17 @@ set_base_rel_pathlists(Query *root) * Non-pushed-down clauses will get evaluated as qpquals of * the SubqueryScan node. * + * We can't push down into subqueries with LIMIT or DISTINCT ON + * clauses, either. + * * XXX Are there any cases where we want to make a policy * decision not to push down, because it'd result in a worse * plan? */ - if (rte->subquery->setOperations == NULL) + if (rte->subquery->setOperations == NULL && + rte->subquery->limitOffset == NULL && + rte->subquery->limitCount == NULL && + !has_distinct_on_clause(rte->subquery)) { /* OK to consider pushing down individual quals */ List *upperrestrictlist = NIL; diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index 21b1dedac9..3cee43b729 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -729,6 +729,58 @@ pull_constant_clauses(List *quals, List **constantQual) } +/***************************************************************************** + * Tests on clauses of queries + * + * Possibly this code should go someplace else, since this isn't quite the + * same meaning of "clause" as is used elsewhere in this module. But I can't + * think of a better place for it... + *****************************************************************************/ + +/* + * Test whether a query uses DISTINCT ON, ie, has a distinct-list that is + * just a subset of the output columns. + */ +bool +has_distinct_on_clause(Query *query) +{ + List *targetList; + + /* Is there a DISTINCT clause at all? */ + if (query->distinctClause == NIL) + return false; + /* + * If the DISTINCT list contains all the nonjunk targetlist items, + * then it's a simple DISTINCT, else it's DISTINCT ON. We do not + * require the lists to be in the same order (since the parser may + * have adjusted the DISTINCT clause ordering to agree with ORDER BY). + */ + foreach(targetList, query->targetList) + { + TargetEntry *tle = (TargetEntry *) lfirst(targetList); + Index ressortgroupref; + List *distinctClause; + + if (tle->resdom->resjunk) + continue; + ressortgroupref = tle->resdom->ressortgroupref; + if (ressortgroupref == 0) + return true; /* definitely not in DISTINCT list */ + foreach(distinctClause, query->distinctClause) + { + SortClause *scl = (SortClause *) lfirst(distinctClause); + + if (scl->tleSortGroupRef == ressortgroupref) + break; /* found TLE in DISTINCT */ + } + if (distinctClause == NIL) + return true; /* this TLE is not in DISTINCT list */ + } + /* It's a simple DISTINCT */ + return false; +} + + /***************************************************************************** * * * General clause-manipulating routines * @@ -736,7 +788,7 @@ pull_constant_clauses(List *quals, List **constantQual) *****************************************************************************/ /* - * clause_relids_vars + * clause_get_relids_vars * Retrieves distinct relids and vars appearing within a clause. * * '*relids' is set to an integer list of all distinct "varno"s appearing diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c index 4533a20783..edc818637b 100644 --- a/src/backend/utils/adt/ruleutils.c +++ b/src/backend/utils/adt/ruleutils.c @@ -119,7 +119,6 @@ static void get_utility_query_def(Query *query, deparse_context *context); static void get_basic_select_query(Query *query, deparse_context *context); static void get_setop_query(Node *setOp, Query *query, deparse_context *context, bool toplevel); -static bool simple_distinct(List *distinctClause, List *targetList); static void get_rule_sortgroupclause(SortClause *srt, List *tlist, bool force_colno, deparse_context *context); @@ -1006,9 +1005,7 @@ get_basic_select_query(Query *query, deparse_context *context) /* Add the DISTINCT clause if given */ if (query->distinctClause != NIL) { - if (simple_distinct(query->distinctClause, query->targetList)) - appendStringInfo(buf, " DISTINCT"); - else + if (has_distinct_on_clause(query)) { appendStringInfo(buf, " DISTINCT ON ("); sep = ""; @@ -1023,6 +1020,8 @@ get_basic_select_query(Query *query, deparse_context *context) } appendStringInfo(buf, ")"); } + else + appendStringInfo(buf, " DISTINCT"); } /* Then we tell what to select (the targetlist) */ @@ -1149,34 +1148,6 @@ get_setop_query(Node *setOp, Query *query, deparse_context *context, } } -/* - * Detect whether a DISTINCT list can be represented as just DISTINCT - * or needs DISTINCT ON. It's simple if it contains exactly the nonjunk - * targetlist items. - */ -static bool -simple_distinct(List *distinctClause, List *targetList) -{ - while (targetList) - { - TargetEntry *tle = (TargetEntry *) lfirst(targetList); - - if (!tle->resdom->resjunk) - { - if (distinctClause == NIL) - return false; - if (((SortClause *) lfirst(distinctClause))->tleSortGroupRef != - tle->resdom->ressortgroupref) - return false; - distinctClause = lnext(distinctClause); - } - targetList = lnext(targetList); - } - if (distinctClause != NIL) - return false; - return true; -} - /* * Display a sort/group clause. */ diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h index 38dcceea3d..ab08b7f6a7 100644 --- a/src/include/optimizer/clauses.h +++ b/src/include/optimizer/clauses.h @@ -59,6 +59,8 @@ extern bool contain_noncachable_functions(Node *clause); extern bool is_pseudo_constant_clause(Node *clause); extern List *pull_constant_clauses(List *quals, List **constantQual); +extern bool has_distinct_on_clause(Query *query); + extern void clause_get_relids_vars(Node *clause, Relids *relids, List **vars); extern int NumRelids(Node *clause); extern void get_relattval(Node *clause, int targetrelid,