Subject: Re: [BUGS] subquery results bypassed From: Tom Lane To: woody+postgresqlbugs@switchonline.com.au, pgsql-bugs@postgresql.org Date: Tue, 31 Jul 2001 14:43:51 -0400 Comments: In-reply-to pgsql-bugs@postgresql.org message dated "Mon, 30 Jul 2001 22:57:20 -0400" Anthony Wood (woody+postgresqlbugs@switchonline.com.au) writes: > [ SELECT DISTINCT ON in a subquery-in-FROM misbehaves ] Here's the patch against 7.1.2 to fix this problem. This also fixes a related problem noted a few days ago, that outer WHERE clauses shouldn't be pushed down into a sub-select that has a LIMIT clause. regards, tom lane *** src/backend/optimizer/path/allpaths.c.orig Wed Mar 21 22:59:34 2001 --- src/backend/optimizer/path/allpaths.c Tue Jul 31 14:05:05 2001 *************** *** 125,135 **** * Non-pushed-down clauses will get evaluated as qpquals of * the SubqueryScan node. * * 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) { /* OK to consider pushing down individual quals */ List *upperrestrictlist = NIL; --- 125,141 ---- * 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 && ! rte->subquery->limitOffset == NULL && ! rte->subquery->limitCount == NULL && ! !has_distinct_on_clause(rte->subquery)) { /* OK to consider pushing down individual quals */ List *upperrestrictlist = NIL; *** src/backend/optimizer/util/clauses.c.orig Tue Mar 27 12:12:34 2001 --- src/backend/optimizer/util/clauses.c Tue Jul 31 14:05:01 2001 *************** *** 730,742 **** /***************************************************************************** * * * General clause-manipulating routines * * * *****************************************************************************/ /* ! * clause_relids_vars * Retrieves distinct relids and vars appearing within a clause. * * '*relids' is set to an integer list of all distinct "varno"s appearing --- 730,794 ---- /***************************************************************************** + * 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 * * * *****************************************************************************/ /* ! * 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 *** src/backend/utils/adt/ruleutils.c.orig Wed Apr 18 13:04:24 2001 --- src/backend/utils/adt/ruleutils.c Tue Jul 31 14:04:51 2001 *************** *** 119,125 **** 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); --- 119,124 ---- *************** *** 1006,1014 **** /* Add the DISTINCT clause if given */ if (query->distinctClause != NIL) { ! if (simple_distinct(query->distinctClause, query->targetList)) ! appendStringInfo(buf, " DISTINCT"); ! else { appendStringInfo(buf, " DISTINCT ON ("); sep = ""; --- 1005,1011 ---- /* Add the DISTINCT clause if given */ if (query->distinctClause != NIL) { ! if (has_distinct_on_clause(query)) { appendStringInfo(buf, " DISTINCT ON ("); sep = ""; *************** *** 1023,1028 **** --- 1020,1027 ---- } appendStringInfo(buf, ")"); } + else + appendStringInfo(buf, " DISTINCT"); } /* Then we tell what to select (the targetlist) */ *************** *** 1147,1180 **** elog(ERROR, "get_setop_query: unexpected node %d", (int) nodeTag(setOp)); } - } - - /* - * 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; } /* --- 1146,1151 ---- *** src/include/optimizer/clauses.h.orig Wed Mar 21 23:00:53 2001 --- src/include/optimizer/clauses.h Tue Jul 31 14:04:35 2001 *************** *** 59,64 **** --- 59,66 ---- 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, ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://www.postgresql.org/search.mpl