*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.77 2001/07/16 17:57:02 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.78 2001/07/31 17:56:30 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* the quals down into the component queries of the setop, but getting it
* right seems nontrivial. Work on this later.)
*
- * 2. If the subquery has a LIMIT clause we must not push down any quals,
- * since that could change the set of rows returned.
+ * 2. If the subquery has a LIMIT clause or a DISTINCT ON clause, we must
+ * not push down any quals, since that could change the set of rows
+ * returned. (Actually, we could push down quals into a DISTINCT ON
+ * subquery if they refer only to DISTINCT-ed output columns, but checking
+ * that seems more work than it's worth. In any case, a plain DISTINCT is
+ * safe to push down past.)
*
* 3. We do not push down clauses that contain subselects, mainly because
* I'm not sure it will work correctly (the subplan hasn't yet transformed
*/
if (subquery->setOperations == NULL &&
subquery->limitOffset == NULL &&
- subquery->limitCount == NULL)
+ subquery->limitCount == NULL &&
+ !has_distinct_on_clause(subquery))
{
/* OK to consider pushing down individual quals */
List *upperrestrictlist = NIL;
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.86 2001/06/19 22:39:11 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/util/clauses.c,v 1.87 2001/07/31 17:56:31 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
}
+/*****************************************************************************
+ * 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_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
* back to source text
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/ruleutils.c,v 1.80 2001/07/16 05:06:59 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/ruleutils.c,v 1.81 2001/07/31 17:56:31 tgl Exp $
*
* This software is copyrighted by Jan Wieck - Hamburg.
*
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);
/* 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 = "";
}
appendStringInfo(buf, ")");
}
+ else
+ appendStringInfo(buf, " DISTINCT");
}
/* Then we tell what to select (the targetlist) */
}
}
-/*
- * 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.
*/
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: clauses.h,v 1.44 2001/05/20 20:28:20 tgl Exp $
+ * $Id: clauses.h,v 1.45 2001/07/31 17:56:31 tgl Exp $
*
*-------------------------------------------------------------------------
*/
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 CommuteClause(Expr *clause);
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