From 967e8a37abcb389809fd35c7b54d8d0de4c5496f Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 2 Feb 2003 19:08:57 +0000
Subject: [PATCH] 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.
---
src/backend/executor/nodeUnique.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/src/backend/executor/nodeUnique.c b/src/backend/executor/nodeUnique.c
index 7a0ccb0b14c..fb012a5cc40 100644
--- 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;
--
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