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Teach planner how to propagate pathkeys from sub-SELECTs in FROM up to

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the outer query.  (The implementation is a bit klugy, but it would take
nontrivial restructuring to make it nicer, which this is probably not
worth.)  This avoids unnecessary sort steps in examples like
SELECT foo,count(*) FROM (SELECT ... ORDER BY foo,bar) sub GROUP BY foo
which means there is now a reasonable technique for controlling the
order of inputs to custom aggregates, even in the grouping case.
This commit is contained in:
Tom Lane
2003-02-15 20:12:41 +00:00
parent 50c4190e37
commit 056467ec6b
9 changed files with 172 additions and 29 deletions
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6
src/backend/optimizer/util/pathnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.87 2003/02/08 20:20:55 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.88 2003/02/15 20:12:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -676,13 +676,13 @@ hash_safe_tlist(List *tlist)
* returning the pathnode.
*/
Path *
create_subqueryscan_path(RelOptInfo *rel)
create_subqueryscan_path(RelOptInfo *rel, List *pathkeys)
{
Path *pathnode = makeNode(Path);
pathnode->pathtype = T_SubqueryScan;
pathnode->parent = rel;
pathnode->pathkeys = NIL; /* for now, assume unordered result */
pathnode->pathkeys = pathkeys;
/* just copy the subplan's cost estimates */
pathnode->startup_cost = rel->subplan->startup_cost;