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, 13 insertions, 1 deletions

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 1ac0ff6ee87..925155c64d4 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -41,6 +41,13 @@
 #define IsBooleanOpfamily(opfamily) \
 	((opfamily) == BOOL_BTREE_FAM_OID || (opfamily) == BOOL_HASH_FAM_OID)
 
+/* Whether to use ScalarArrayOpExpr to build index qualifications */
+typedef enum
+{
+	SAOP_FORBID,				/* Do not use ScalarArrayOpExpr */
+	SAOP_ALLOW,					/* OK to use ScalarArrayOpExpr */
+	SAOP_REQUIRE				/* Require ScalarArrayOpExpr */
+} SaOpControl;
 
 /* Whether we are looking for plain indexscan, bitmap scan, or either */
 typedef enum
@@ -78,6 +85,11 @@ static PathClauseUsage *classify_index_clause_usage(Path *path,
 							List **clauselist);
 static void find_indexpath_quals(Path *bitmapqual, List **quals, List **preds);
 static int	find_list_position(Node *node, List **nodelist);
+static List *group_clauses_by_indexkey(IndexOptInfo *index,
+						  List *clauses, List *outer_clauses,
+						  Relids outer_relids,
+						  SaOpControl saop_control,
+						  bool *found_clause);
 static bool match_clause_to_indexcol(IndexOptInfo *index,
 						 int indexcol,
 						 RestrictInfo *rinfo,
@@ -1060,7 +1072,7 @@ find_list_position(Node *node, List **nodelist)
  * from multiple places.  Defend against redundant outputs by using
  * list_append_unique_ptr (pointer equality should be good enough).
  */
-List *
+static List *
 group_clauses_by_indexkey(IndexOptInfo *index,
 						  List *clauses, List *outer_clauses,
 						  Relids outer_relids,