Do not allow Unique nodes to be scanned backwards. The code claimed that it

would work, but in fact it didn't return the same rows when moving backwards
as when moving forwards.  This would have no visible effect in a DISTINCT
query (at least assuming the column datatypes use a strong definition of
equality), but it gave entirely wrong answers for DISTINCT ON queries.

diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c
index be65336c109fbe6af0613a52ae77af5320c1e111..3a8e3f0d5174a35cc37ddede240b982ba5ab55c6 100644 (file)
--- a/src/backend/executor/execAmi.c
+++ b/src/backend/executor/execAmi.c
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *     $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.85.2.2 2008/07/10 01:17:52 tgl Exp $
+ *     $PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.85.2.3 2008/08/05 21:28:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -383,9 +383,6 @@ ExecSupportsBackwardScan(Plan *node)
                case T_Sort:
                        return true;
 
-               case T_Unique:
-                       return ExecSupportsBackwardScan(outerPlan(node));
-
                case T_Limit:
                        return ExecSupportsBackwardScan(outerPlan(node));