From 884f9dfee1b263c1b1780e85b5d646a91835a1c8 Mon Sep 17 00:00:00 2001
From: Haojun Liao <hjliao@taosdata.com>
Date: Fri, 23 Dec 2022 00:56:03 +0800
Subject: [PATCH] fix(query): set start row index for desc scan.

---
 source/dnode/vnode/src/tsdb/tsdbMergeTree.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/source/dnode/vnode/src/tsdb/tsdbMergeTree.c b/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
index f75ad51afd..e2019fb783 100644
--- a/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
+++ b/source/dnode/vnode/src/tsdb/tsdbMergeTree.c
@@ -501,7 +501,10 @@ bool tLDataIterNextRow(SLDataIter *pIter, const char *idStr) {
 
     if (iBlockL != pIter->iSttBlk) {
       pBlockData = loadLastBlock(pIter, idStr);
-      pIter->iRow += step;
+      if (pBlockData == NULL) {
+        goto _exit;
+      }
+      pIter->iRow = pIter->backward? pBlockData->nRow-1:0;
     }
   }