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Fix optimizer to not try to push WHERE clauses down into a sub-SELECT that

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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.
This commit is contained in:
Tom Lane
2001-07-31 17:56:31 +00:00
parent 6fbf442d5a
commit 421467cdc8
4 changed files with 70 additions and 40 deletions
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13
src/backend/optimizer/path/allpaths.c
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@ -8,7 +8,7 @@
*
*
* 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 $
*
*-------------------------------------------------------------------------
*/
@ -296,8 +296,12 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
* 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
@ -311,7 +315,8 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
*/
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;