Allows the following query to succeed: "SELECT NULL ORDER BY 1;"

There are three or four cases in transformSortClause() and I had fixed
only one case for UNION. A second case is now fixed, in the same way; I
assigned INT4OID to the column type for the "won't actually happen"
sort. Didn't want to skip the code entirely, since the backend needs to
_try_ a sort to get the NULLs right. I'm not certain under what
circumstances the other cases are invoked and these are not yet
fixed up, though perhaps they don't need to be...

src/backend/parser/parse_clause.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.21 1998/07/14 03:51:42 thomas Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_clause.c,v 1.22 1998/08/02 13:34:26 thomas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -317,6 +317,10 @@ transformSortClause(ParseState *pstate,
 {
 	List	   *s = NIL;
 
+#ifdef PARSEDEBUG
+printf("transformSortClause: entering\n");
+#endif
+
 	while (orderlist != NIL)
 	{
 		SortGroupBy *sortby = lfirst(orderlist);
@@ -326,7 +330,17 @@ transformSortClause(ParseState *pstate,
 
 		restarget = find_targetlist_entry(pstate, sortby, targetlist);
 
+#ifdef PARSEDEBUG
+printf("transformSortClause: find sorting operator for type %d\n",
+  restarget->resdom->restype);
+#endif
+
 		sortcl->resdom = resdom = restarget->resdom;
+
+		/* if we have InvalidOid, then this is a NULL field and don't need to sort */
+		if (resdom->restype == InvalidOid)
+			resdom->restype = INT4OID;
+
 		sortcl->opoid = oprid(oper(sortby->useOp,
 								   resdom->restype,
 								   resdom->restype, false));
@@ -389,6 +403,14 @@ transformSortClause(ParseState *pstate,
 					/* not a member of the sortclauses yet */
 					SortClause *sortcl = makeNode(SortClause);
 
+#ifdef PARSEDEBUG
+printf("transformSortClause: (2) find sorting operator for type %d\n",
+  tlelt->resdom->restype);
+#endif
+
+					if (tlelt->resdom->restype == InvalidOid)
+						tlelt->resdom->restype = INT4OID;
+
 					sortcl->resdom = tlelt->resdom;
 					sortcl->opoid = any_ordering_op(tlelt->resdom->restype);
 
@@ -423,6 +445,11 @@ transformSortClause(ParseState *pstate,
 				/* not a member of the sortclauses yet */
 				SortClause *sortcl = makeNode(SortClause);
 
+#ifdef PARSEDEBUG
+printf("transformSortClause: try sorting type %d\n",
+  tlelt->resdom->restype);
+#endif
+
 				sortcl->resdom = tlelt->resdom;
 				sortcl->opoid = any_ordering_op(tlelt->resdom->restype);
 
@@ -485,6 +512,13 @@ printf("transformUnionClause: types are %d -> %d\n", itype, otype);
 					{
 						((TargetEntry *)lfirst(prev_target))->resdom->restype = itype;
 					}
+#if FALSE
+					else
+					{
+						((TargetEntry *)lfirst(prev_target))->resdom->restype = UNKNOWNOID;
+						((TargetEntry *)lfirst(next_target))->resdom->restype = UNKNOWNOID;
+					}
+#endif
 				}
 				else if (itype == InvalidOid)
 				{