Improve pull_up_subqueries logic so that it doesn't insert unnecessary

PlaceHolderVar nodes in join quals appearing in or below the lowest
outer join that could null the subquery being pulled up.  This improves
the planner's ability to recognize constant join quals, and probably
helps with detection of common sort keys (equivalence classes) as well.

src/backend/optimizer/plan/planner.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.254 2009/04/19 19:46:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.255 2009/04/28 21:31:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -324,7 +324,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	 * this query.
 	 */
 	parse->jointree = (FromExpr *)
-		pull_up_subqueries(root, (Node *) parse->jointree, false, false);
+		pull_up_subqueries(root, (Node *) parse->jointree, NULL, NULL);
 
 	/*
 	 * Detect whether any rangetable entries are RTE_JOIN kind; if not, we can

src/include/optimizer/prep.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.64 2009/01/01 17:24:00 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.65 2009/04/28 21:31:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,7 +24,8 @@
 extern void pull_up_sublinks(PlannerInfo *root);
 extern void inline_set_returning_functions(PlannerInfo *root);
 extern Node *pull_up_subqueries(PlannerInfo *root, Node *jtnode,
-				   bool below_outer_join, bool append_rel_member);
+				   JoinExpr *lowest_outer_join,
+				   AppendRelInfo *containing_appendrel);
 extern void reduce_outer_joins(PlannerInfo *root);
 extern Relids get_relids_in_jointree(Node *jtnode, bool include_joins);
 extern Relids get_relids_for_join(PlannerInfo *root, int joinrelid);