Repair two constraint-exclusion corner cases triggered by proving that an

inheritance child of an UPDATE/DELETE target relation can be excluded by
constraints.  I had rearranged some code in set_append_rel_pathlist() to
avoid "useless" work when a child is excluded, but overdid it and left
the child with no cheapest_path entry, causing possible failure later
if the appendrel was involved in a join.  Also, it seems that the dummy
plan generated by inheritance_planner() when all branches are excluded
has to be a bit less dummy now than was required in 8.2.
Per report from Jan Wieck.  Add his test case to the regression tests.

src/backend/optimizer/path/allpaths.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.163 2007/04/21 21:01:44 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.164 2007/05/26 18:23:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,6 +45,7 @@ static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					   RangeTblEntry *rte);
 static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 						Index rti, RangeTblEntry *rte);
+static void set_dummy_rel_pathlist(RelOptInfo *rel);
 static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 					  Index rti, RangeTblEntry *rte);
 static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel,
@@ -198,23 +199,14 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 {
 	/*
 	 * If we can prove we don't need to scan the rel via constraint exclusion,
-	 * set up a single dummy path for it.  (Rather than inventing a special
-	 * "dummy" path type, we represent this as an AppendPath with no members.)
-	 * We only need to check for regular baserels; if it's an otherrel, CE
-	 * was already checked in set_append_rel_pathlist().
+	 * set up a single dummy path for it.  We only need to check for regular
+	 * baserels; if it's an otherrel, CE was already checked in
+	 * set_append_rel_pathlist().
 	 */
 	if (rel->reloptkind == RELOPT_BASEREL &&
 		relation_excluded_by_constraints(rel, rte))
 	{
-		/* Set dummy size estimates --- we leave attr_widths[] as zeroes */
-		rel->rows = 0;
-		rel->width = 0;
-
-		add_path(rel, (Path *) create_append_path(rel, NIL));
-
-		/* Select cheapest path (pretty easy in this case...) */
-		set_cheapest(rel);
-
+		set_dummy_rel_pathlist(rel);
 		return;
 	}
 
@@ -330,7 +322,12 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 
 		if (relation_excluded_by_constraints(childrel, childRTE))
 		{
-			/* this child need not be scanned, so just disregard it */
+			/*
+			 * This child need not be scanned, so we can omit it from the
+			 * appendrel.  Mark it with a dummy cheapest-path though, in
+			 * case best_appendrel_indexscan() looks at it later.
+			 */
+			set_dummy_rel_pathlist(childrel);
 			continue;
 		}
 
@@ -425,6 +422,26 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 	set_cheapest(rel);
 }
 
+/*
+ * set_dummy_rel_pathlist
+ *	  Build a dummy path for a relation that's been excluded by constraints
+ *
+ * Rather than inventing a special "dummy" path type, we represent this as an
+ * AppendPath with no members.
+ */
+static void
+set_dummy_rel_pathlist(RelOptInfo *rel)
+{
+	/* Set dummy size estimates --- we leave attr_widths[] as zeroes */
+	rel->rows = 0;
+	rel->width = 0;
+
+	add_path(rel, (Path *) create_append_path(rel, NIL));
+
+	/* Select cheapest path (pretty easy in this case...) */
+	set_cheapest(rel);
+}
+
 /* quick-and-dirty test to see if any joining is needed */
 static bool
 has_multiple_baserels(PlannerInfo *root)

src/backend/optimizer/plan/planner.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.220 2007/05/25 17:54:25 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.221 2007/05/26 18:23:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -669,11 +669,16 @@ inheritance_planner(PlannerInfo *root)
 	 * If we managed to exclude every child rel, return a dummy plan
 	 */
 	if (subplans == NIL)
+	{
+		root->resultRelations = list_make1_int(parentRTindex);
+		/* although dummy, it must have a valid tlist for executor */
+		tlist = preprocess_targetlist(root, parse->targetList);
 		return (Plan *) make_result(root,
 									tlist,
 									(Node *) list_make1(makeBoolConst(false,
 																	  false)),
 									NULL);
+	}
 
 	/*
 	 * Planning might have modified the rangetable, due to changes of the

src/test/regress/expected/rules.out

@@ -1493,3 +1493,61 @@ select * from id_ordered;
 
 set client_min_messages to warning; -- suppress cascade notices
 drop table id cascade;
+reset client_min_messages;
+--
+-- check corner case where an entirely-dummy subplan is created by
+-- constraint exclusion
+--
+create temp table t1 (a integer primary key);
+NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t1_pkey" for table "t1"
+create temp table t1_1 (check (a >= 0 and a < 10)) inherits (t1);
+create temp table t1_2 (check (a >= 10 and a < 20)) inherits (t1);
+create rule t1_ins_1 as on insert to t1 
+	where new.a >= 0 and new.a < 10
+	do instead
+	insert into t1_1 values (new.a);
+create rule t1_ins_2 as on insert to t1 
+	where new.a >= 10 and new.a < 20
+	do instead
+	insert into t1_2 values (new.a);
+create rule t1_upd_1 as on update to t1
+	where old.a >= 0 and old.a < 10
+	do instead
+	update t1_1 set a = new.a where a = old.a;
+create rule t1_upd_2 as on update to t1
+	where old.a >= 10 and old.a < 20
+	do instead
+	update t1_2 set a = new.a where a = old.a;
+set constraint_exclusion = on;
+insert into t1 select * from generate_series(5,19,1) g;
+update t1 set a = 4 where a = 5;
+select * from only t1;
+ a 
+---
+(0 rows)
+
+select * from only t1_1;
+ a 
+---
+ 6
+ 7
+ 8
+ 9
+ 4
+(5 rows)
+
+select * from only t1_2;
+ a  
+----
+ 10
+ 11
+ 12
+ 13
+ 14
+ 15
+ 16
+ 17
+ 18
+ 19
+(10 rows)
+

src/test/regress/sql/rules.sql

@@ -881,3 +881,41 @@ select * from id_ordered;
 
 set client_min_messages to warning; -- suppress cascade notices
 drop table id cascade;
+reset client_min_messages;
+
+--
+-- check corner case where an entirely-dummy subplan is created by
+-- constraint exclusion
+--
+
+create temp table t1 (a integer primary key);
+
+create temp table t1_1 (check (a >= 0 and a < 10)) inherits (t1);
+create temp table t1_2 (check (a >= 10 and a < 20)) inherits (t1);
+
+create rule t1_ins_1 as on insert to t1 
+	where new.a >= 0 and new.a < 10
+	do instead
+	insert into t1_1 values (new.a);
+create rule t1_ins_2 as on insert to t1 
+	where new.a >= 10 and new.a < 20
+	do instead
+	insert into t1_2 values (new.a);
+
+create rule t1_upd_1 as on update to t1
+	where old.a >= 0 and old.a < 10
+	do instead
+	update t1_1 set a = new.a where a = old.a;
+create rule t1_upd_2 as on update to t1
+	where old.a >= 10 and old.a < 20
+	do instead
+	update t1_2 set a = new.a where a = old.a;
+
+set constraint_exclusion = on;
+
+insert into t1 select * from generate_series(5,19,1) g;
+update t1 set a = 4 where a = 5;
+
+select * from only t1;
+select * from only t1_1;
+select * from only t1_2;