Handle constants correctly in cdbpullup_findPathKeyExprInTargetList

If a PathKey contains a constant member, it can be evaluated without
any entries in the target list, and can always be returned in
cdbpullup_findPathKeyExprInTargetList. This fixes the "Unexpected intarnal
error" you got with the included test query.

Closes issue #348, reported by liruto. Thanks for the report!

src/backend/cdb/cdbpullup.c

@@ -379,52 +379,53 @@ cdbpullup_findPathKeyExprInTargetList(PathKey *item, List *targetlist)
 	ListCell *lc;
 	EquivalenceClass *eclass = item->pk_eclass;
 
-	/* Bail if targetlist is empty. */
-	if (!targetlist)
-		return NULL;
-
 	foreach(lc, eclass->ec_members)
 	{
 		EquivalenceMember *em = (EquivalenceMember *) lfirst(lc);
 		Expr	   *key = (Expr *) em->em_expr;
-		TargetEntry *tle;
 
+		/* A constant is OK regardless of the target list */
 		if (em->em_is_const)
 			return key;
 
-		/* Ignore possible RelabelType node atop the PathKey expr. */
-		if (IsA(key, RelabelType))
-			key = ((RelabelType *)key)->arg;
-
-		/* Check if targetlist is a List of TargetEntry */
-		if (IsA(linitial(targetlist), TargetEntry))
-		{
-			tle = tlist_member_ignoring_RelabelType(key, targetlist);
-			if (tle)
-				return key;
-		}
-		/* Planner's RelOptInfo targetlists don't have TargetEntry nodes */
-		else
+		if (targetlist)
 		{
-			ListCell *tcell;
+			/* Ignore possible RelabelType node atop the PathKey expr. */
+			if (IsA(key, RelabelType))
+				key = ((RelabelType *)key)->arg;
 
-			foreach(tcell, targetlist)
+			/* Check if targetlist is a List of TargetEntry */
+			if (IsA(linitial(targetlist), TargetEntry))
 			{
-				Expr *expr = (Expr *) lfirst(tcell);
+				TargetEntry *tle;
 
-				if (IsA(expr, RelabelType))
-					expr = ((RelabelType *)expr)->arg;
-
-				if (equal(expr, key))
+				tle = tlist_member_ignoring_RelabelType(key, targetlist);
+				if (tle)
 					return key;
 			}
-		}
+			/* Planner's RelOptInfo targetlists don't have TargetEntry nodes */
+			else
+			{
+				ListCell *tcell;
 
-		/* Return this item if all referenced Vars are in targetlist. */
-		if (!IsA(key, Var) &&
-			!cdbpullup_missingVarWalker((Node *) key, targetlist))
-		{
-			return key;
+				foreach(tcell, targetlist)
+				{
+					Expr *expr = (Expr *) lfirst(tcell);
+
+					if (IsA(expr, RelabelType))
+						expr = ((RelabelType *)expr)->arg;
+
+					if (equal(expr, key))
+						return key;
+				}
+			}
+
+			/* Return this item if all referenced Vars are in targetlist. */
+			if (!IsA(key, Var) &&
+				!cdbpullup_missingVarWalker((Node *) key, targetlist))
+			{
+				return key;
+			}
 		}
 	}
 

src/test/regress/expected/subselect_gp.out

@@ -1247,3 +1247,16 @@ where s_suppkey in (
  foo10
 (1 row)
 
+--
+-- Another case that failed at one point. (A planner bug in pulling up a
+-- subquery with constant distribution key, 1, in the outer queries.)
+--
+create table nested_in_tbl(tc1 int, tc2 int) distributed by (tc1);
+select * from nested_in_tbl t1  where tc1 in
+  (select 1 from nested_in_tbl t2 where tc1 in
+    (select 1 from nested_in_tbl t3 where t3.tc2 = t2.tc2));
+ tc1 | tc2 
+-----+-----
+(0 rows)
+
+drop table nested_in_tbl;

src/test/regress/expected/subselect_gp_optimizer.out

@@ -1260,3 +1260,16 @@ where s_suppkey in (
  foo10
 (1 row)
 
+--
+-- Another case that failed at one point. (A planner bug in pulling up a
+-- subquery with constant distribution key, 1, in the outer queries.)
+--
+create table nested_in_tbl(tc1 int, tc2 int) distributed by (tc1);
+select * from nested_in_tbl t1  where tc1 in
+  (select 1 from nested_in_tbl t2 where tc1 in
+    (select 1 from nested_in_tbl t3 where t3.tc2 = t2.tc2));
+ tc1 | tc2 
+-----+-----
+(0 rows)
+
+drop table nested_in_tbl;

src/test/regress/sql/subselect_gp.sql

@@ -568,3 +568,13 @@ select s_name from xsupplier
 where s_suppkey in (
   select g.l_suppkey from xlineitem g
 ) ;
+
+--
+-- Another case that failed at one point. (A planner bug in pulling up a
+-- subquery with constant distribution key, 1, in the outer queries.)
+--
+create table nested_in_tbl(tc1 int, tc2 int) distributed by (tc1);
+select * from nested_in_tbl t1  where tc1 in
+  (select 1 from nested_in_tbl t2 where tc1 in
+    (select 1 from nested_in_tbl t3 where t3.tc2 = t2.tc2));
+drop table nested_in_tbl;