From: Darren King <darrenk@insightdist.com>

scrappy · scrappy · commit 20e11f290976 · 1998-01-26T00:21:02.000Z
I have always been under the impression that NULL is not equal to
NULL and that NULL is not equal to anything else either.  If this
is the case, then this patch is correct.

If NULL _is_ equal to NULL, then I think there are other problems
in the Group By logic.
diff --git a/src/backend/executor/nodeGroup.c b/src/backend/executor/nodeGroup.c
@@ -13,7 +13,7 @@
  *	  columns. (ie. tuples from the same group are consecutive)
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeGroup.c,v 1.11 1997/10/27 12:00:43 vadim Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeGroup.c,v 1.12 1998/01/26 00:21:02 scrappy Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -415,8 +415,11 @@ sameGroup(TupleTableSlot *oldslot,
 
 		if (isNull1 == isNull2)
 		{
-			if (isNull1)		/* both are null, they are equal */
-				continue;
+			/* both are null, they are _not_ equal since
+			 * NULL is not equal to NULL (or anything).
+			 *   --  25 Jan 1998  --  darrenk */
+			if (isNull1)
+				return FALSE;
 
 			val1 = fmgr(typoutput, attr1,
 						gettypelem(tupdesc->attrs[att - 1]->atttypid));
