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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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8
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 1.96 2003/02/08 20:20:54 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/allpaths.c,v 1.97 2003/02/15 20:12:40 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -291,6 +291,7 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
Index rti, RangeTblEntry *rte)
{
Query *subquery = rte->subquery;
List *pathkeys;
/*
* If there are any restriction clauses that have been attached to the
@ -351,8 +352,11 @@ set_subquery_pathlist(Query *root, RelOptInfo *rel,
/* Mark rel with estimated output rows, width, etc */
set_baserel_size_estimates(root, rel);
/* Convert subquery pathkeys to outer representation */
pathkeys = build_subquery_pathkeys(root, rel, subquery);
/* Generate appropriate path */
add_path(rel, create_subqueryscan_path(rel));
add_path(rel, create_subqueryscan_path(rel, pathkeys));
/* Select cheapest path (pretty easy in this case...) */
set_cheapest(rel);