From 174b552e711c337535481dbbb35c1b7a3caa101b Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Tue, 13 Apr 1999 17:18:29 +0000
Subject: There are some bugs about backward scanning using indexes.

1. Index Scan using plural indexids never scan backward
   as to the order of indexids.
2. The cursor using Index scan is not usable after moving
   past the end.

This patch solves above bugs.
Moreover the change of _bt_first() would be useful to extend
ORDER BY patch by Jan Wieck for all descending order cases.

Hiroshi Inoue
---
 src/backend/executor/nodeIndexscan.c | 42 +++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 8 deletions(-)

(limited to 'src/backend/executor/nodeIndexscan.c')

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index cdf13c5e19e..16bb4f23b41 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v 1.33 1999/02/21 03:48:40 scrappy Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v 1.34 1999/04/13 17:18:29 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -96,6 +96,8 @@ IndexNext(IndexScan *node)
 	Buffer		buffer = InvalidBuffer;
 	int			numIndices;
 
+ 	bool		bBackward;
+ 	int		indexNumber;
 	/* ----------------
 	 *	extract necessary information from index scan node
 	 * ----------------
@@ -151,8 +153,26 @@ IndexNext(IndexScan *node)
 	 *	appropriate heap tuple.. else return NULL.
 	 * ----------------
 	 */
-	while (indexstate->iss_IndexPtr < numIndices)
-	{
+ 	bBackward = ScanDirectionIsBackward(direction);
+ 	if (bBackward)
+  	{
+ 		indexNumber = numIndices - indexstate->iss_IndexPtr - 1;
+ 		if (indexNumber < 0)
+ 		{
+ 			indexNumber = 0;
+ 			indexstate->iss_IndexPtr = numIndices - 1;
+ 		}
+ 	}
+ 	else
+ 	{
+ 		if ((indexNumber = indexstate->iss_IndexPtr) < 0)
+ 		{
+ 			indexNumber = 0;
+ 			indexstate->iss_IndexPtr = 0;
+ 		}
+ 	}
+ 	while (indexNumber < numIndices)
+ 	{
 		scandesc = scanDescs[indexstate->iss_IndexPtr];
 		while ((result = index_getnext(scandesc, direction)) != NULL)
 		{
@@ -204,8 +224,14 @@ IndexNext(IndexScan *node)
 			if (BufferIsValid(buffer))
 				ReleaseBuffer(buffer);
 		}
-		if (indexstate->iss_IndexPtr < numIndices)
-			indexstate->iss_IndexPtr++;
+ 		if (indexNumber < numIndices)
+ 		{
+ 			indexNumber++;
+ 			if (bBackward)
+ 				indexstate->iss_IndexPtr--;
+ 			else
+ 				indexstate->iss_IndexPtr++;
+ 		}
 	}
 	/* ----------------
 	 *	if we get here it means the index scan failed so we
@@ -294,7 +320,7 @@ ExecIndexReScan(IndexScan *node, ExprContext *exprCtxt, Plan *parent)
 	runtimeKeyInfo = (Pointer *) indexstate->iss_RuntimeKeyInfo;
 	indxqual = node->indxqual;
 	numScanKeys = indexstate->iss_NumScanKeys;
-	indexstate->iss_IndexPtr = 0;
+	indexstate->iss_IndexPtr = -1;
 
 	/* If this is re-scanning of PlanQual ... */
 	if (estate->es_evTuple != NULL && 
@@ -611,7 +637,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate, Plan *parent)
 	  */
 	indexstate = makeNode(IndexScanState);
 	indexstate->iss_NumIndices = 0;
-	indexstate->iss_IndexPtr = 0;
+	indexstate->iss_IndexPtr = -1;
 	indexstate->iss_ScanKeys = NULL;
 	indexstate->iss_NumScanKeys = NULL;
 	indexstate->iss_RuntimeKeyInfo = NULL;
@@ -635,7 +661,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate, Plan *parent)
 	indxid = node->indxid;
 	indxqual = node->indxqual;
 	numIndices = length(indxid);
-	indexPtr = 0;
+	indexPtr = -1;
 
 	CXT1_printf("ExecInitIndexScan: context is %d\n", CurrentMemoryContext);
 
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