Fix nodeUnique to behave correctly when reversing direction after reaching

either end of subplan results.  This prevents misbehavior of cursors
on SELECT DISTINCT ... queries.  Per bug report 1-Feb-02.

diff --git a/src/backend/executor/nodeUnique.c b/src/backend/executor/nodeUnique.c
index 7a0ccb0..fb012a5 100644 (file)
--- a/src/backend/executor/nodeUnique.c
+++ b/src/backend/executor/nodeUnique.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/executor/nodeUnique.c,v 1.37 2003/01/10 23:54:24 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/executor/nodeUnique.c,v 1.38 2003/02/02 19:08:57 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -56,6 +56,11 @@ ExecUnique(UniqueState *node)
        /*
         * now loop, returning only non-duplicate tuples. We assume that the
         * tuples arrive in sorted order so we can detect duplicates easily.
+        *
+        * We return the first tuple from each group of duplicates (or the
+        * last tuple of each group, when moving backwards).  At either end
+        * of the subplan, clear priorTuple so that we correctly return the
+        * first/last tuple when reversing direction.
         */
        for (;;)
        {
@@ -64,10 +69,16 @@ ExecUnique(UniqueState *node)
                 */
                slot = ExecProcNode(outerPlan);
                if (TupIsNull(slot))
+               {
+                       /* end of subplan; reset in case we change direction */
+                       if (node->priorTuple != NULL)
+                               heap_freetuple(node->priorTuple);
+                       node->priorTuple = NULL;
                        return NULL;
+               }
 
                /*
-                * Always return the first tuple from the subplan.
+                * Always return the first/last tuple from the subplan.
                 */
                if (node->priorTuple == NULL)
                        break;