From 059576a3a50baabbc68971bf6ba87cd98c00ea54 Mon Sep 17 00:00:00 2001
From: wangmm0220 <wangmm0220@gmail.com>
Date: Mon, 16 Aug 2021 13:28:07 +0800
Subject: [PATCH] [6046]<fix> fix ts always in first output index using
 derivative function

---
 src/query/src/qExecutor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/query/src/qExecutor.c b/src/query/src/qExecutor.c
index 9000bcdf77..af7408880a 100644
--- a/src/query/src/qExecutor.c
+++ b/src/query/src/qExecutor.c
@@ -3622,7 +3622,7 @@ void updateOutputBuf(SOptrBasicInfo* pBInfo, int32_t *bufCapacity, int32_t numOf
     // re-estabilish output buffer pointer.
     int32_t functionId = pBInfo->pCtx[i].functionId;
     if (functionId == TSDB_FUNC_TOP || functionId == TSDB_FUNC_BOTTOM || functionId == TSDB_FUNC_DIFF || functionId == TSDB_FUNC_DERIVATIVE) {
-      pBInfo->pCtx[i].ptsOutputBuf = pBInfo->pCtx[i-1].pOutput;
+      if(i > 0) pBInfo->pCtx[i].ptsOutputBuf = pBInfo->pCtx[i-1].pOutput;
     }
   }
 }