From d80ec2aad82d4075238ff2e8cf464bf0cd85f1a1 Mon Sep 17 00:00:00 2001
From: hjxilinx <hjxilinx@163.com>
Date: Fri, 31 Jan 2020 23:29:39 +0800
Subject: [PATCH] fix bugs #1170.  [tbase-1492]

---
 src/client/src/tscFunctionImpl.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/client/src/tscFunctionImpl.c b/src/client/src/tscFunctionImpl.c
index 22875593c2..058a0e045b 100644
--- a/src/client/src/tscFunctionImpl.c
+++ b/src/client/src/tscFunctionImpl.c
@@ -3024,14 +3024,14 @@ static void diff_function(SQLFunctionCtx *pCtx) {
         if (pCtx->param[1].nType == INITIAL_VALUE_NOT_ASSIGNED) {  // initial value is not set yet
           pCtx->param[1].i64Key = pData[i];
           pCtx->param[1].nType = pCtx->inputType;
-        } else if (i == 0) {
+        } else if ((i == 0 && pCtx->order == TSQL_SO_ASC) || (i == pCtx->size - 1 && pCtx->order == TSQL_SO_DESC)) {
           *pOutput = pData[i] - pCtx->param[1].i64Key;
           *pTimestamp = pCtx->ptsList[i];
 
           pOutput += step;
           pTimestamp += step;
         } else {
-          *pOutput = pData[i] - pData[i - 1];
+          *pOutput = pData[i] - pData[i - step];
           *pTimestamp = pCtx->ptsList[i];
 
           pOutput += step;
@@ -3056,13 +3056,13 @@ static void diff_function(SQLFunctionCtx *pCtx) {
         if (pCtx->param[1].nType == INITIAL_VALUE_NOT_ASSIGNED) {  // initial value is not set yet
           pCtx->param[1].dKey = pData[i];
           pCtx->param[1].nType = pCtx->inputType;
-        } else if (i == 0) {
+        } else if ((i == 0 && pCtx->order == TSQL_SO_ASC) || (i == pCtx->size - 1 && pCtx->order == TSQL_SO_DESC)) {
           *pOutput = pData[i] - pCtx->param[1].dKey;
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
         } else {
-          *pOutput = pData[i] - pData[i - 1];
+          *pOutput = pData[i] - pData[i - step];
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
@@ -3086,13 +3086,13 @@ static void diff_function(SQLFunctionCtx *pCtx) {
         if (pCtx->param[1].nType == INITIAL_VALUE_NOT_ASSIGNED) {  // initial value is not set yet
           pCtx->param[1].dKey = pData[i];
           pCtx->param[1].nType = pCtx->inputType;
-        } else if (i == 0) {
+        } else if ((i == 0 && pCtx->order == TSQL_SO_ASC) || (i == pCtx->size - 1 && pCtx->order == TSQL_SO_DESC)) {
           *pOutput = pData[i] - pCtx->param[1].dKey;
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
         } else {
-          *pOutput = pData[i] - pData[i - 1];
+          *pOutput = pData[i] - pData[i - step];
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
@@ -3117,13 +3117,13 @@ static void diff_function(SQLFunctionCtx *pCtx) {
         if (pCtx->param[1].nType == INITIAL_VALUE_NOT_ASSIGNED) {  // initial value is not set yet
           pCtx->param[1].i64Key = pData[i];
           pCtx->param[1].nType = pCtx->inputType;
-        } else if (i == 0) {
+        } else if ((i == 0 && pCtx->order == TSQL_SO_ASC) || (i == pCtx->size - 1 && pCtx->order == TSQL_SO_DESC)) {
           *pOutput = pData[i] - pCtx->param[1].i64Key;
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
         } else {
-          *pOutput = pData[i] - pData[i - 1];
+          *pOutput = pData[i] - pData[i - step];
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
@@ -3147,13 +3147,13 @@ static void diff_function(SQLFunctionCtx *pCtx) {
         if (pCtx->param[1].nType == INITIAL_VALUE_NOT_ASSIGNED) {  // initial value is not set yet
           pCtx->param[1].i64Key = pData[i];
           pCtx->param[1].nType = pCtx->inputType;
-        } else if (i == 0) {
+        } else if ((i == 0 && pCtx->order == TSQL_SO_ASC) || (i == pCtx->size - 1 && pCtx->order == TSQL_SO_DESC)) {
           *pOutput = pData[i] - pCtx->param[1].i64Key;
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
         } else {
-          *pOutput = pData[i] - pData[i - 1];
+          *pOutput = pData[i] - pData[i - step];
           *pTimestamp = pCtx->ptsList[i];
           pOutput += step;
           pTimestamp += step;
-- 
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