diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 90485171d9..033aaba494 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -16,7 +16,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.15 2004/01/10 00:30:21 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/prep/prepjointree.c,v 1.16 2004/01/10 18:13:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -439,11 +439,13 @@ is_simple_subquery(Query *subquery)
 /*
  * has_nullable_targetlist
  *	  Check a subquery in the range table to see if all the non-junk
- *	  targetlist items are simple variables (and, hence, will correctly
- *	  go to NULL when examined above the point of an outer join).
+ *	  targetlist items are simple variables or strict functions of simple
+ *	  variables (and, hence, will correctly go to NULL when examined above
+ *	  the point of an outer join).
  *
- * A possible future extension is to accept strict functions of simple
- * variables, eg, "x + 1".
+ * NOTE: it would be correct (and useful) to ignore output columns that aren't
+ * actually referenced by the enclosing query ... but we do not have that
+ * information available at this point.
  */
 static bool
 has_nullable_targetlist(Query *subquery)
@@ -458,11 +460,15 @@ has_nullable_targetlist(Query *subquery)
 		if (tle->resdom->resjunk)
 			continue;
 
-		/* Okay if tlist item is a simple Var */
-		if (tle->expr && IsA(tle->expr, Var))
-			continue;
+		/* Must contain a Var of current level */
+		if (!contain_vars_of_level((Node *) tle->expr, 0))
+			return false;
 
-		return false;
+		/* Must not contain any non-strict constructs */
+		if (contain_nonstrict_functions((Node *) tle->expr))
+			return false;
+
+		/* This one's OK, keep scanning */
 	}
 	return true;
 }
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index b2b2d7d02b..6ce171e2f1 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.160 2004/01/05 18:04:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.161 2004/01/10 18:13:53 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -697,10 +697,10 @@ contain_volatile_functions_walker(Node *node, void *context)
  * Returns true if any nonstrict construct is found --- ie, anything that
  * could produce non-NULL output with a NULL input.
  *
- * XXX we do not examine sub-selects to see if they contain uses of
- * nonstrict functions. It's not real clear if that is correct or not...
- * for the current usage it does not matter, since inline_function()
- * rejects cases with sublinks.
+ * The idea here is that the caller has verified that the expression contains
+ * one or more Var or Param nodes (as appropriate for the caller's need), and
+ * now wishes to prove that the expression result will be NULL if any of these
+ * inputs is NULL.  If we return false, then the proof succeeded.
  */
 bool
 contain_nonstrict_functions(Node *clause)
@@ -713,6 +713,11 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 {
 	if (node == NULL)
 		return false;
+	if (IsA(node, Aggref))
+	{
+		/* an aggregate could return non-null with null input */
+		return true;
+	}
 	if (IsA(node, FuncExpr))
 	{
 		FuncExpr   *expr = (FuncExpr *) node;
@@ -745,16 +750,25 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 
 		switch (expr->boolop)
 		{
-			case OR_EXPR:
 			case AND_EXPR:
-				/* OR, AND are inherently non-strict */
+			case OR_EXPR:
+				/* AND, OR are inherently non-strict */
 				return true;
 			default:
 				break;
 		}
 	}
+	if (IsA(node, SubLink))
+	{
+		/* In some cases a sublink might be strict, but in general not */
+		return true;
+	}
+	if (IsA(node, SubPlan))
+		return true;
 	if (IsA(node, CaseExpr))
 		return true;
+	if (IsA(node, CaseWhen))
+		return true;
 	/* NB: ArrayExpr might someday be nonstrict */
 	if (IsA(node, CoalesceExpr))
 		return true;
@@ -764,18 +778,6 @@ contain_nonstrict_functions_walker(Node *node, void *context)
 		return true;
 	if (IsA(node, BooleanTest))
 		return true;
-	if (IsA(node, SubLink))
-	{
-		SubLink    *sublink = (SubLink *) node;
-		List	   *opid;
-
-		foreach(opid, sublink->operOids)
-		{
-			if (!op_strict(lfirsto(opid)))
-				return true;
-		}
-		/* else fall through to check args */
-	}
 	return expression_tree_walker(node, contain_nonstrict_functions_walker,
 								  context);
 }