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.

diff --git a/src/backend/utils/sort/lselect.c b/src/backend/utils/sort/lselect.c
index 230b0b0..ae10049 100644 (file)
--- a/src/backend/utils/sort/lselect.c
+++ b/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;
 }