Reimplement planner's handling of MIN/MAX aggregate optimization (again).

Instead of playing cute games with pathkeys, just build a direct
representation of the intended sub-select, and feed it through
query_planner to get a Path for the index access.  This is a bit slower
than 9.1's previous method, since we'll duplicate most of the overhead of
query_planner; but since the whole optimization only applies to rather
simple single-table queries, that probably won't be much of a problem in
practice.  The advantage is that we get to do the right thing when there's
a partial index that needs the implicit IS NOT NULL clause to be usable.
Also, although this makes planagg.c be a bit more closely tied to the
ordering of operations in grouping_planner, we can get rid of some coupling
to lower-level parts of the planner.  Per complaint from Marti Raudsepp.

1 files changed, 0 insertions, 9 deletions

diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index d0e872b6466..3dc23662e71 100644
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -440,18 +440,9 @@ query_planner(PlannerInfo *root, List *tlist,
 static void
 canonicalize_all_pathkeys(PlannerInfo *root)
 {
-	ListCell   *lc;
-
 	root->query_pathkeys = canonicalize_pathkeys(root, root->query_pathkeys);
 	root->group_pathkeys = canonicalize_pathkeys(root, root->group_pathkeys);
 	root->window_pathkeys = canonicalize_pathkeys(root, root->window_pathkeys);
 	root->distinct_pathkeys = canonicalize_pathkeys(root, root->distinct_pathkeys);
 	root->sort_pathkeys = canonicalize_pathkeys(root, root->sort_pathkeys);
-
-	foreach(lc, root->minmax_aggs)
-	{
-		MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
-
-		mminfo->pathkeys = canonicalize_pathkeys(root, mminfo->pathkeys);
-	}
 }