diff --git a/src/client/src/tscFunctionImpl.c b/src/client/src/tscFunctionImpl.c
index 22875593c246029dddca7c663466affe8447ec3b..058a0e045b63ffa5dd078b4fce27752d3a0f7913 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;
diff --git a/src/system/detail/src/vnodeQueryImpl.c b/src/system/detail/src/vnodeQueryImpl.c
index 0daa0936e9bdcf237955dc97f11b8679aeb8ecf0..c1653b5dad85689e3fabe1b150dd06cb7c9cdec8 100644
--- a/src/system/detail/src/vnodeQueryImpl.c
+++ b/src/system/detail/src/vnodeQueryImpl.c
@@ -4525,10 +4525,11 @@ static void doSetTagValueInParam(tTagSchema *pTagSchema, int32_t tagColIdx, SMet
   SSchema *pCol = &pTagSchema->pSchema[tagColIdx];
 
   tVariantDestroy(param);
-  tVariantCreateFromBinary(param, pStr, pCol->bytes, pCol->type);
 
   if (isNull(pStr, pCol->type)) {
     param->nType = TSDB_DATA_TYPE_NULL;
+  } else {
+    tVariantCreateFromBinary(param, pStr, pCol->bytes, pCol->type);
   }
 }
 
@@ -5993,10 +5994,13 @@ int32_t getDataBlocksForMeters(SMeterQuerySupportObj *pSupporter, SQuery *pQuery
     size_t  bufferSize = size + sizeof(TSCKSUM);
     
     pMeterDataInfo[j]->numOfBlocks = compInfo.numOfBlocks;
-    pMeterDataInfo[j]->pBlock = calloc(1, bufferSize);
-    if (pMeterDataInfo[j]->pBlock == NULL) {
+    char* p = realloc(pMeterDataInfo[j]->pBlock, bufferSize);
+    if (p == NULL) {
       clearAllMeterDataBlockInfo(pMeterDataInfo, 0, numOfMeters);
       return TSDB_CODE_SERV_OUT_OF_MEMORY;
+    } else {
+      memset(p, 0, bufferSize);
+      pMeterDataInfo[j]->pBlock = (SCompBlock*) p;
     }
   
     read(pVnodeFileInfo->headerFd, pMeterDataInfo[j]->pBlock, bufferSize);
diff --git a/src/system/detail/src/vnodeQueryProcess.c b/src/system/detail/src/vnodeQueryProcess.c
index 1783a1a0b4ee2a78812568baba5caf3cffbccf7f..8ad2c3f3094a948580b54ade88283d06f499a674 100644
--- a/src/system/detail/src/vnodeQueryProcess.c
+++ b/src/system/detail/src/vnodeQueryProcess.c
@@ -573,10 +573,10 @@ static void vnodeMultiMeterMultiOutputProcessor(SQInfo *pQInfo) {
   tSidSet *pSids = pSupporter->pSidSet;
 
   SMeterObj *pOneMeter = getMeterObj(pSupporter->pMeterObj, pMeterSidExtInfo[0]->sid);
-
-  resetCtxOutputBuf(pRuntimeEnv);
-
+  
   if (isPointInterpoQuery(pQuery)) {
+    resetCtxOutputBuf(pRuntimeEnv);
+  
     assert(pQuery->limit.offset == 0 && pQuery->limit.limit != 0);
 
     while (pSupporter->subgroupIdx < pSids->numOfSubSet) {
@@ -663,7 +663,9 @@ static void vnodeMultiMeterMultiOutputProcessor(SQInfo *pQInfo) {
     if (pSupporter->meterIdx >= pSids->numOfSids) {
       return;
     }
-
+  
+    resetCtxOutputBuf(pRuntimeEnv);
+  
     for (int32_t i = 0; i < pRuntimeEnv->usedIndex; ++i) {
       SOutputRes *pOneRes = &pRuntimeEnv->pResult[i];
       clearGroupResultBuf(pOneRes, pQuery->numOfOutputCols);