Fix tuplecmp() to ensure repeatable sort ordering of tuples

that contain null fields.  Old code would produce erratic sort results
because comparisons of tuples containing nulls could produce inconsistent
answers.

src/backend/utils/sort/lselect.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/sort/Attic/lselect.c,v 1.15 1999/02/13 23:20:15 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/sort/Attic/lselect.c,v 1.16 1999/07/10 18:21:59 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -186,41 +186,49 @@ puttuple(struct leftist ** treep,
 int
 tuplecmp(HeapTuple ltup, HeapTuple rtup, LeftistContext context)
 {
-	Datum		lattr,
-				rattr;
-	int			nkey = 0;
+	int			nkey;
 	int			result = 0;
-	bool		isnull;
 
 	if (ltup == (HeapTuple) NULL)
 		return 0;
 	if (rtup == (HeapTuple) NULL)
 		return 1;
-	while (nkey < context->nKeys && !result)
+	for (nkey = 0; nkey < context->nKeys; nkey++)
 	{
-		lattr = heap_getattr(ltup,
-							 context->scanKeys[nkey].sk_attno,
-							 context->tupDesc, &isnull);
-		if (isnull)
-			return 0;
-		rattr = heap_getattr(rtup,
-							 context->scanKeys[nkey].sk_attno,
-							 context->tupDesc,
-							 &isnull);
-		if (isnull)
+		ScanKey		thisKey = & context->scanKeys[nkey];
+		Datum		lattr,
+					rattr;
+		bool		lisnull,
+					risnull;
+
+		lattr = heap_getattr(ltup, thisKey->sk_attno,
+							 context->tupDesc, &lisnull);
+		rattr = heap_getattr(rtup, thisKey->sk_attno,
+							 context->tupDesc, &risnull);
+		if (lisnull)
+		{
+			if (risnull)
+				continue;		/* treat two nulls as equal */
+			return 0;			/* else, a null sorts after all else */
+		}
+		if (risnull)
 			return 1;
-		if (context->scanKeys[nkey].sk_flags & SK_COMMUTE)
+		if (thisKey->sk_flags & SK_COMMUTE)
+		{
+			if (!(result =
+				  (long) (*fmgr_faddr(&thisKey->sk_func)) (rattr, lattr)))
+				result =
+					-(long) (*fmgr_faddr(&thisKey->sk_func)) (lattr, rattr);
+		}
+		else
 		{
 			if (!(result =
-				  (long) (*fmgr_faddr(&context->scanKeys[nkey].sk_func)) (rattr, lattr)))
+				  (long) (*fmgr_faddr(&thisKey->sk_func)) (lattr, rattr)))
 				result =
-					-(long) (*fmgr_faddr(&context->scanKeys[nkey].sk_func)) (lattr, rattr);
+					-(long) (*fmgr_faddr(&thisKey->sk_func)) (rattr, lattr);
 		}
-		else if (!(result =
-				   (long) (*fmgr_faddr(&context->scanKeys[nkey].sk_func)) (lattr, rattr)))
-			result =
-				-(long) (*fmgr_faddr(&context->scanKeys[nkey].sk_func)) (rattr, lattr);
-		nkey++;
+		if (result)
+			break;
 	}
 	return result == 1;
 }