diff --git a/src/client/inc/tscUtil.h b/src/client/inc/tscUtil.h
index f747184ce017e9cb780ba2a61b87360cee0379d8..448fee936f5c4ad6d5428638b531d8ac742a1648 100644
--- a/src/client/inc/tscUtil.h
+++ b/src/client/inc/tscUtil.h
@@ -123,6 +123,7 @@ int32_t tscGetDataBlockFromList(SHashObj* pHashList, int64_t id, int32_t size, i
  */
 bool tscIsPointInterpQuery(SQueryInfo* pQueryInfo);
 bool tscIsTWAQuery(SQueryInfo* pQueryInfo);
+bool tscIsDiffQuery(SQueryInfo* pQueryInfo);
 bool tscIsSessionWindowQuery(SQueryInfo* pQueryInfo);
 bool tscIsSecondStageQuery(SQueryInfo* pQueryInfo);
 bool tsIsArithmeticQueryOnAggResult(SQueryInfo* pQueryInfo);
@@ -132,7 +133,6 @@ bool hasTagValOutput(SQueryInfo* pQueryInfo);
 bool timeWindowInterpoRequired(SQueryInfo *pQueryInfo);
 bool isStabledev(SQueryInfo* pQueryInfo);
 bool isTsCompQuery(SQueryInfo* pQueryInfo);
-bool isSimpleAggregate(SQueryInfo* pQueryInfo);
 bool isBlockDistQuery(SQueryInfo* pQueryInfo);
 bool isSimpleAggregateRv(SQueryInfo* pQueryInfo);
 
@@ -331,7 +331,7 @@ SVgroupsInfo* tscVgroupsInfoDup(SVgroupsInfo* pVgroupsInfo);
 int32_t tscCreateQueryFromQueryInfo(SQueryInfo* pQueryInfo, SQueryAttr* pQueryAttr, void* addr);
 
 void tsCreateSQLFunctionCtx(SQueryInfo* pQueryInfo, SQLFunctionCtx* pCtx, SSchema* pSchema);
-void* createQInfoFromQueryNode(SQueryInfo* pQueryInfo, STableGroupInfo* pTableGroupInfo, SOperatorInfo* pOperator, char* sql, void* addr, int32_t stage);
+void* createQInfoFromQueryNode(SQueryInfo* pQueryInfo, STableGroupInfo* pTableGroupInfo, SOperatorInfo* pOperator, char* sql, void* addr, int32_t stage, uint64_t qId);
 
 void* malloc_throw(size_t size);
 void* calloc_throw(size_t nmemb, size_t size);
diff --git a/src/client/inc/tsclient.h b/src/client/inc/tsclient.h
index 67fd34ffd7425cf921e927247149808540de3020..46aad90c42a0a4872f4961163d5722a7900f29d0 100644
--- a/src/client/inc/tsclient.h
+++ b/src/client/inc/tsclient.h
@@ -319,7 +319,7 @@ int32_t tscCreateResPointerInfo(SSqlRes *pRes, SQueryInfo *pQueryInfo);
 void tscSetResRawPtr(SSqlRes* pRes, SQueryInfo* pQueryInfo);
 void tscSetResRawPtrRv(SSqlRes* pRes, SQueryInfo* pQueryInfo, SSDataBlock* pBlock);
 
-void handleDownstreamOperator(SSqlObj** pSqlList, int32_t numOfUpstream, SQueryInfo* px, SSqlRes* pOutput);
+void handleDownstreamOperator(SSqlObj** pSqlList, int32_t numOfUpstream, SQueryInfo* px, SSqlObj* pParent);
 void destroyTableNameList(SInsertStatementParam* pInsertParam);
 
 void tscResetSqlCmd(SSqlCmd *pCmd, bool removeMeta);
diff --git a/src/client/src/tscAsync.c b/src/client/src/tscAsync.c
index 15276a38887523541cbe37ebf1add2152d2ffe80..d857d00e159d06df266187693913a6b6e404a2b3 100644
--- a/src/client/src/tscAsync.c
+++ b/src/client/src/tscAsync.c
@@ -144,7 +144,7 @@ static void tscAsyncFetchRowsProxy(void *param, TAOS_RES *tres, int numOfRows) {
   }
   
   // local merge has handle this situation during super table non-projection query.
-  if (pCmd->command != TSDB_SQL_RETRIEVE_LOCALMERGE) {
+  if (pCmd->command != TSDB_SQL_RETRIEVE_GLOBALMERGE) {
     pRes->numOfClauseTotal += pRes->numOfRows;
   }
 
@@ -174,7 +174,7 @@ static void tscProcessAsyncRetrieveImpl(void *param, TAOS_RES *tres, int numOfRo
   }
 
   pSql->fp = fp;
-  if (pCmd->command != TSDB_SQL_RETRIEVE_LOCALMERGE && pCmd->command < TSDB_SQL_LOCAL) {
+  if (pCmd->command != TSDB_SQL_RETRIEVE_GLOBALMERGE && pCmd->command < TSDB_SQL_LOCAL) {
     pCmd->command = (pCmd->command > TSDB_SQL_MGMT) ? TSDB_SQL_RETRIEVE : TSDB_SQL_FETCH;
   }
 
@@ -257,14 +257,14 @@ void taos_fetch_rows_a(TAOS_RES *tres, __async_cb_func_t fp, void *param) {
       }
 
       return;
-    } else if (pCmd->command == TSDB_SQL_RETRIEVE || pCmd->command == TSDB_SQL_RETRIEVE_LOCALMERGE) {
+    } else if (pCmd->command == TSDB_SQL_RETRIEVE || pCmd->command == TSDB_SQL_RETRIEVE_GLOBALMERGE) {
       // in case of show command, return no data
       (*pSql->fetchFp)(param, pSql, 0);
     } else {
       assert(0);
     }
   } else { // current query is not completed, continue retrieve from node
-    if (pCmd->command != TSDB_SQL_RETRIEVE_LOCALMERGE && pCmd->command < TSDB_SQL_LOCAL) {
+    if (pCmd->command != TSDB_SQL_RETRIEVE_GLOBALMERGE && pCmd->command < TSDB_SQL_LOCAL) {
       pCmd->command = (pCmd->command > TSDB_SQL_MGMT) ? TSDB_SQL_RETRIEVE : TSDB_SQL_FETCH;
     }
 
diff --git a/src/client/src/tscLocal.c b/src/client/src/tscLocal.c
index f97f54a6267d2754cb2edf2fd38ff6c075a2b285..2c9717306f2b26dfbbb5ec1d676b5baad3eb2d2d 100644
--- a/src/client/src/tscLocal.c
+++ b/src/client/src/tscLocal.c
@@ -323,7 +323,7 @@ TAOS_ROW tscFetchRow(void *param) {
   // current data set are exhausted, fetch more data from node
   if (pRes->row >= pRes->numOfRows && (pRes->completed != true || hasMoreVnodesToTry(pSql) || hasMoreClauseToTry(pSql)) &&
       (pCmd->command == TSDB_SQL_RETRIEVE ||
-       pCmd->command == TSDB_SQL_RETRIEVE_LOCALMERGE ||
+       pCmd->command == TSDB_SQL_RETRIEVE_GLOBALMERGE ||
        pCmd->command == TSDB_SQL_TABLE_JOIN_RETRIEVE ||
        pCmd->command == TSDB_SQL_FETCH ||
        pCmd->command == TSDB_SQL_SHOW ||
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 15e40d59187a4eabd7c01caf7733da118deb548d..5d712bb980f92ebaf99979b5fd551e4203a50edd 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -2928,8 +2928,8 @@ void tscRestoreFuncForSTableQuery(SQueryInfo* pQueryInfo) {
 }
 
 bool hasUnsupportFunctionsForSTableQuery(SSqlCmd* pCmd, SQueryInfo* pQueryInfo) {
-  const char* msg1 = "TWA not allowed to apply to super table directly";
-  const char* msg2 = "TWA only support group by tbname for super table query";
+  const char* msg1 = "TWA/Diff not allowed to apply to super table directly";
+  const char* msg2 = "TWA/Diff only support group by tbname for super table query";
   const char* msg3 = "function not support for super table query";
 
   // filter sql function not supported by metric query yet.
@@ -2942,7 +2942,7 @@ bool hasUnsupportFunctionsForSTableQuery(SSqlCmd* pCmd, SQueryInfo* pQueryInfo)
     }
   }
 
-  if (tscIsTWAQuery(pQueryInfo)) {
+  if (tscIsTWAQuery(pQueryInfo) || tscIsDiffQuery(pQueryInfo)) {
     if (pQueryInfo->groupbyExpr.numOfGroupCols == 0) {
       invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg1);
       return true;
@@ -6276,7 +6276,7 @@ int32_t doFunctionsCompatibleCheck(SSqlCmd* pCmd, SQueryInfo* pQueryInfo) {
       }
 
       if (IS_MULTIOUTPUT(aAggs[functId].status) && functId != TSDB_FUNC_TOP && functId != TSDB_FUNC_BOTTOM &&
-          functId != TSDB_FUNC_TAGPRJ && functId != TSDB_FUNC_PRJ) {
+          functId != TSDB_FUNC_DIFF && functId != TSDB_FUNC_TAGPRJ && functId != TSDB_FUNC_PRJ) {
         return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg1);
       }
 
@@ -6758,7 +6758,7 @@ int32_t doCheckForStream(SSqlObj* pSql, SSqlInfo* pInfo) {
   const char* msg6 = "from missing in subclause";
   const char* msg7 = "time interval is required";
   const char* msg8 = "the first column should be primary timestamp column";
-  
+
   SSqlCmd*    pCmd = &pSql->cmd;
   SQueryInfo* pQueryInfo = tscGetQueryInfo(pCmd);
   assert(pQueryInfo->numOfTables == 1);
@@ -7719,6 +7719,7 @@ int32_t validateSqlNode(SSqlObj* pSql, SSqlNode* pSqlNode, SQueryInfo* pQueryInf
 
     pQueryInfo->arithmeticOnAgg = tsIsArithmeticQueryOnAggResult(pQueryInfo);
     pQueryInfo->orderProjectQuery = tscOrderedProjectionQueryOnSTable(pQueryInfo, 0);
+    pQueryInfo->diffQuery = tscIsDiffQuery(pQueryInfo);
 
     SExprInfo** p = NULL;
     int32_t numOfExpr = 0;
diff --git a/src/client/src/tscServer.c b/src/client/src/tscServer.c
index 27630053036db1afa5b6f75eda620f58b3ec62be..0fd8d6a0c74566ba9d5ea778d06b4d2dc6fcf872 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -1588,7 +1588,7 @@ int tscProcessLocalRetrieveRsp(SSqlObj *pSql) {
   return tscLocalResultCommonBuilder(pSql, numOfRes);
 }
 
-int tscProcessRetrieveLocalMergeRsp(SSqlObj *pSql) {
+int tscProcessRetrieveGlobalMergeRsp(SSqlObj *pSql) {
   SSqlRes *pRes = &pSql->res;
   SSqlCmd* pCmd = &pSql->cmd;
 
@@ -1615,10 +1615,11 @@ int tscProcessRetrieveLocalMergeRsp(SSqlObj *pSql) {
     taosArrayPush(group, &tableKeyInfo);
     taosArrayPush(tableGroupInfo.pGroupList, &group);
 
-    pQueryInfo->pQInfo = createQInfoFromQueryNode(pQueryInfo, &tableGroupInfo, NULL, NULL, pRes->pMerger, MERGE_STAGE);
+    tscDebug("0x%"PRIx64" create QInfo 0x%"PRIx64" to execute query processing", pSql->self, pSql->self);
+    pQueryInfo->pQInfo = createQInfoFromQueryNode(pQueryInfo, &tableGroupInfo, NULL, NULL, pRes->pMerger, MERGE_STAGE, pSql->self);
   }
 
-  uint64_t localQueryId = 0;
+  uint64_t localQueryId = pSql->self;
   qTableQuery(pQueryInfo->pQInfo, &localQueryId);
   convertQueryResult(pRes, pQueryInfo);
 
@@ -2689,7 +2690,7 @@ void tscInitMsgsFp() {
 
   tscProcessMsgRsp[TSDB_SQL_RETRIEVE_EMPTY_RESULT] = tscProcessEmptyResultRsp;
 
-  tscProcessMsgRsp[TSDB_SQL_RETRIEVE_LOCALMERGE] = tscProcessRetrieveLocalMergeRsp;
+  tscProcessMsgRsp[TSDB_SQL_RETRIEVE_GLOBALMERGE] = tscProcessRetrieveGlobalMergeRsp;
 
   tscProcessMsgRsp[TSDB_SQL_ALTER_TABLE] = tscProcessAlterTableMsgRsp;
   tscProcessMsgRsp[TSDB_SQL_ALTER_DB] = tscProcessAlterDbMsgRsp;
diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index 554ce351eb05a3196a08a79c3b3067df6de6aab8..1e9389287674996b63ff3a7cc2d8ece81d4bc130 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -456,7 +456,7 @@ static bool needToFetchNewBlock(SSqlObj* pSql) {
 
   return (pRes->completed != true || hasMoreVnodesToTry(pSql) || hasMoreClauseToTry(pSql)) &&
          (pCmd->command == TSDB_SQL_RETRIEVE ||
-          pCmd->command == TSDB_SQL_RETRIEVE_LOCALMERGE ||
+          pCmd->command == TSDB_SQL_RETRIEVE_GLOBALMERGE ||
           pCmd->command == TSDB_SQL_TABLE_JOIN_RETRIEVE ||
           pCmd->command == TSDB_SQL_FETCH ||
           pCmd->command == TSDB_SQL_SHOW ||
diff --git a/src/client/src/tscSubquery.c b/src/client/src/tscSubquery.c
index 4b1b3e9080fe9078380540792cb2c8835acc33dc..431357bf08fd3285f4276d29d66e2020569e5a66 100644
--- a/src/client/src/tscSubquery.c
+++ b/src/client/src/tscSubquery.c
@@ -2422,7 +2422,7 @@ int32_t tscHandleMasterSTableQuery(SSqlObj *pSql) {
   
   // pRes->code check only serves in launching metric sub-queries
   if (pRes->code == TSDB_CODE_TSC_QUERY_CANCELLED) {
-    pCmd->command = TSDB_SQL_RETRIEVE_LOCALMERGE;  // enable the abort of kill super table function.
+    pCmd->command = TSDB_SQL_RETRIEVE_GLOBALMERGE;  // enable the abort of kill super table function.
     return pRes->code;
   }
   
@@ -2778,7 +2778,7 @@ static void tscAllDataRetrievedFromDnode(SRetrieveSupport *trsupport, SSqlObj* p
   if (code == TSDB_CODE_SUCCESS && trsupport->pExtMemBuffer == NULL) {
     pParentSql->cmd.command = TSDB_SQL_RETRIEVE_EMPTY_RESULT; // no result, set the result empty
   } else {
-    pParentSql->cmd.command = TSDB_SQL_RETRIEVE_LOCALMERGE;
+    pParentSql->cmd.command = TSDB_SQL_RETRIEVE_GLOBALMERGE;
   }
 
   tscCreateResPointerInfo(&pParentSql->res, pPQueryInfo);
@@ -3500,7 +3500,7 @@ static UNUSED_FUNC bool tscHasRemainDataInSubqueryResultSet(SSqlObj *pSql) {
 }
 
 void* createQInfoFromQueryNode(SQueryInfo* pQueryInfo, STableGroupInfo* pTableGroupInfo, SOperatorInfo* pSourceOperator,
-    char* sql, void* merger, int32_t stage) {
+                               char* sql, void* merger, int32_t stage, uint64_t qId) {
   assert(pQueryInfo != NULL);
   SQInfo *pQInfo = (SQInfo *)calloc(1, sizeof(SQInfo));
   if (pQInfo == NULL) {
@@ -3509,7 +3509,7 @@ void* createQInfoFromQueryNode(SQueryInfo* pQueryInfo, STableGroupInfo* pTableGr
 
   // to make sure third party won't overwrite this structure
   pQInfo->signature = pQInfo;
-
+  pQInfo->qId       = qId;
   SQueryRuntimeEnv *pRuntimeEnv = &pQInfo->runtimeEnv;
   SQueryAttr       *pQueryAttr  = &pQInfo->query;
 
diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index 8042f032c8a2fad85de23c4f2bbdc5c07670cdc3..7a9e2d2289212155924aad2d291acf478e884c2f 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -222,6 +222,8 @@ bool tscIsProjectionQueryOnSTable(SQueryInfo* pQueryInfo, int32_t tableIndex) {
         functionId != TSDB_FUNC_TS &&
         functionId != TSDB_FUNC_ARITHM &&
         functionId != TSDB_FUNC_TS_COMP &&
+        functionId != TSDB_FUNC_DIFF &&
+        functionId != TSDB_FUNC_TS_DUMMY &&
         functionId != TSDB_FUNC_TID_TAG) {
       return false;
     }
@@ -434,6 +436,23 @@ bool tscIsTWAQuery(SQueryInfo* pQueryInfo) {
 
   return false;
 }
+
+bool tscIsDiffQuery(SQueryInfo* pQueryInfo) {
+  size_t num = tscNumOfExprs(pQueryInfo);
+  for(int32_t i = 0; i < num; ++i) {
+    SExprInfo* pExpr = tscExprGet(pQueryInfo, i);
+    if (pExpr == NULL || pExpr->base.functionId == TSDB_FUNC_TS_DUMMY) {
+      continue;
+    }
+
+    if (pExpr->base.functionId == TSDB_FUNC_DIFF) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 bool tscIsSessionWindowQuery(SQueryInfo* pQueryInfo) {
   return pQueryInfo->sessionWindow.gap > 0;
 }
@@ -467,42 +486,12 @@ bool tscNeedReverseScan(SQueryInfo* pQueryInfo) {
   return false;
 }
 
-bool isSimpleAggregate(SQueryInfo* pQueryInfo) {
-  if (pQueryInfo->interval.interval > 0) {
-    return false;
-  }
-
-  // Note:top/bottom query is fixed output query
-  if (tscIsTopBotQuery(pQueryInfo) || tscGroupbyColumn(pQueryInfo) || isTsCompQuery(pQueryInfo)) {
-    return true;
-  }
-
-  size_t numOfExprs = tscNumOfExprs(pQueryInfo);
-  for (int32_t i = 0; i < numOfExprs; ++i) {
-    SExprInfo* pExpr = tscExprGet(pQueryInfo, i);
-    if (pExpr == NULL) {
-      continue;
-    }
-
-    int32_t functionId = pExpr->base.functionId;
-    if (functionId == TSDB_FUNC_TS || functionId == TSDB_FUNC_TS_DUMMY) {
-      continue;
-    }
-
-    if (!IS_MULTIOUTPUT(aAggs[functionId].status)) {
-      return true;
-    }
-  }
-
-  return false;
-}
-
 bool isSimpleAggregateRv(SQueryInfo* pQueryInfo) {
   if (pQueryInfo->interval.interval > 0 || pQueryInfo->sessionWindow.gap > 0) {
     return false;
   }
 
-  if (tscGroupbyColumn(pQueryInfo) || isTsCompQuery(pQueryInfo)) {
+  if (tscGroupbyColumn(pQueryInfo) || isTsCompQuery(pQueryInfo) || tscIsTopBotQuery(pQueryInfo) || tscIsDiffQuery(pQueryInfo)) {
     return false;
   }
 
@@ -812,6 +801,7 @@ static void fetchNextBlockIfCompleted(SOperatorInfo* pOperator, bool* newgroup)
   for (int32_t i = 0; i < pOperator->numOfUpstream; ++i) {
     SJoinStatus* pStatus = &pJoinInfo->status[i];
     if (pStatus->pBlock == NULL || pStatus->index >= pStatus->pBlock->info.rows) {
+      tscDebug("Retrieve nest query result, index:%d, total:%d", i, pOperator->numOfUpstream);
       pStatus->pBlock = pOperator->upstream[i]->exec(pOperator->upstream[i], newgroup);
       pStatus->index = 0;
 
@@ -1088,7 +1078,9 @@ static void createInputDataFilterInfo(SQueryInfo* px, int32_t numOfCol1, int32_t
   tfree(tableCols);
 }
 
-void handleDownstreamOperator(SSqlObj** pSqlObjList, int32_t numOfUpstream, SQueryInfo* px, SSqlRes* pOutput) {
+void handleDownstreamOperator(SSqlObj** pSqlObjList, int32_t numOfUpstream, SQueryInfo* px, SSqlObj* pSql) {
+  SSqlRes* pOutput = &pSql->res;
+
   // handle the following query process
   if (px->pQInfo == NULL) {
     SColumnInfo* pColumnInfo = extractColumnInfoFromResult(px->colList);
@@ -1166,7 +1158,9 @@ void handleDownstreamOperator(SSqlObj** pSqlObjList, int32_t numOfUpstream, SQue
       }
     }
 
-    px->pQInfo = createQInfoFromQueryNode(px, &tableGroupInfo, pSourceOperator, NULL, NULL, MASTER_SCAN);
+    tscDebug("0x%"PRIx64" create QInfo 0x%"PRIx64" to execute the main query while all nest query is ready", pSql->self, pSql->self);
+    px->pQInfo = createQInfoFromQueryNode(px, &tableGroupInfo, pSourceOperator, NULL, NULL, MASTER_SCAN, pSql->self);
+
     tfree(pColumnInfo);
     tfree(schema);
 
@@ -1174,7 +1168,7 @@ void handleDownstreamOperator(SSqlObj** pSqlObjList, int32_t numOfUpstream, SQue
     pSourceOperator->pRuntimeEnv = &px->pQInfo->runtimeEnv;
   }
 
-  uint64_t qId = 0;
+  uint64_t qId = pSql->self;
   qTableQuery(px->pQInfo, &qId);
   convertQueryResult(pOutput, px);
 }
@@ -1372,7 +1366,7 @@ void tscFreeSqlObj(SSqlObj* pSql) {
 
   SSqlCmd* pCmd = &pSql->cmd;
   int32_t cmd = pCmd->command;
-  if (cmd < TSDB_SQL_INSERT || cmd == TSDB_SQL_RETRIEVE_LOCALMERGE || cmd == TSDB_SQL_RETRIEVE_EMPTY_RESULT ||
+  if (cmd < TSDB_SQL_INSERT || cmd == TSDB_SQL_RETRIEVE_GLOBALMERGE || cmd == TSDB_SQL_RETRIEVE_EMPTY_RESULT ||
       cmd == TSDB_SQL_TABLE_JOIN_RETRIEVE) {
     tscRemoveFromSqlList(pSql);
   }
@@ -3436,7 +3430,7 @@ void doRetrieveSubqueryData(SSchedMsg *pMsg) {
   }
 
   SQueryInfo *pQueryInfo = tscGetQueryInfo(&pSql->cmd);
-  handleDownstreamOperator(pSql->pSubs, pSql->subState.numOfSub, pQueryInfo, &pSql->res);
+  handleDownstreamOperator(pSql->pSubs, pSql->subState.numOfSub, pQueryInfo, pSql);
 
   pSql->res.qId = -1;
   if (pSql->res.code == TSDB_CODE_SUCCESS) {
@@ -4236,10 +4230,11 @@ int32_t tscCreateQueryFromQueryInfo(SQueryInfo* pQueryInfo, SQueryAttr* pQueryAt
   pQueryAttr->hasTagResults     = hasTagValOutput(pQueryInfo);
   pQueryAttr->stabledev         = isStabledev(pQueryInfo);
   pQueryAttr->tsCompQuery       = isTsCompQuery(pQueryInfo);
-  pQueryAttr->simpleAgg         = isSimpleAggregate(pQueryInfo);
+  pQueryAttr->diffQuery         = pQueryInfo->diffQuery;
+  pQueryAttr->simpleAgg         = pQueryInfo->simpleAgg;
   pQueryAttr->needReverseScan   = tscNeedReverseScan(pQueryInfo);
   pQueryAttr->stableQuery       = QUERY_IS_STABLE_QUERY(pQueryInfo->type);
-  pQueryAttr->groupbyColumn     = (!pQueryInfo->stateWindow) && tscGroupbyColumn(pQueryInfo);
+  pQueryAttr->groupbyColumn     = (!pQueryInfo->stateWindow) && pQueryInfo->groupbyColumn;
   pQueryAttr->queryBlockDist    = isBlockDistQuery(pQueryInfo);
   pQueryAttr->pointInterpQuery  = tscIsPointInterpQuery(pQueryInfo);
   pQueryAttr->timeWindowInterpo = timeWindowInterpoRequired(pQueryInfo);
@@ -4255,7 +4250,6 @@ int32_t tscCreateQueryFromQueryInfo(SQueryInfo* pQueryInfo, SQueryAttr* pQueryAt
   pQueryAttr->fillType          = pQueryInfo->fillType;
   pQueryAttr->havingNum         = pQueryInfo->havingFieldNum;
   
-
   if (pQueryInfo->order.order == TSDB_ORDER_ASC) {   // TODO refactor
     pQueryAttr->window = pQueryInfo->window;
   } else {
diff --git a/src/common/inc/tcmdtype.h b/src/common/inc/tcmdtype.h
index adf210cfebb15ddc0adcfce2aa85e606f79c44a5..90426519e66682ab9d5fab16a3a38e827a7d97df 100644
--- a/src/common/inc/tcmdtype.h
+++ b/src/common/inc/tcmdtype.h
@@ -76,7 +76,7 @@ enum {
   // SQL below for client local 
   TSDB_DEFINE_SQL_TYPE( TSDB_SQL_LOCAL, "local" ) 
   TSDB_DEFINE_SQL_TYPE( TSDB_SQL_DESCRIBE_TABLE, "describe-table" )
-  TSDB_DEFINE_SQL_TYPE( TSDB_SQL_RETRIEVE_LOCALMERGE, "retrieve-localmerge" )
+  TSDB_DEFINE_SQL_TYPE( TSDB_SQL_RETRIEVE_GLOBALMERGE, "retrieve-globalmerge" )
   TSDB_DEFINE_SQL_TYPE( TSDB_SQL_TABLE_JOIN_RETRIEVE, "join-retrieve" )
 
   TSDB_DEFINE_SQL_TYPE( TSDB_SQL_SHOW_CREATE_TABLE, "show-create-table")
diff --git a/src/query/inc/qExecutor.h b/src/query/inc/qExecutor.h
index b5b4fb58548f5067c26644cf63e0a5911b69ad8b..93f2b73d7ac6645563b7e830b82206ca00c0dbe0 100644
--- a/src/query/inc/qExecutor.h
+++ b/src/query/inc/qExecutor.h
@@ -185,6 +185,7 @@ typedef struct SQueryAttr {
   bool             queryBlockDist;    // if query data block distribution
   bool             stabledev;        // super table stddev query
   bool             tsCompQuery;      // is tscomp query
+  bool             diffQuery;        // is diff query
   bool             simpleAgg;
   bool             pointInterpQuery; // point interpolation query
   bool             needReverseScan;  // need reverse scan
@@ -386,6 +387,7 @@ typedef struct STableScanInfo {
   int64_t         elapsedTime;
 
   int32_t         tableIndex;
+  int32_t         prevGroupId;     // previous table group id
 } STableScanInfo;
 
 typedef struct STagScanInfo {
diff --git a/src/query/inc/qTableMeta.h b/src/query/inc/qTableMeta.h
index 4fc252b644efab0c6bfdb97b19c3af3ef9c68920..1fd78ed324597ca338824931999bb6c1fa5e1219 100644
--- a/src/query/inc/qTableMeta.h
+++ b/src/query/inc/qTableMeta.h
@@ -138,6 +138,7 @@ typedef struct SQueryInfo {
   bool               hasFilter;
   bool               onlyTagQuery;
   bool               orderProjectQuery;
+  bool               diffQuery;
   bool               stateWindow;
 } SQueryInfo;
 
diff --git a/src/query/src/qAggMain.c b/src/query/src/qAggMain.c
index ba6efcabb2f0788908485d3af246a6e0855ed2a1..74c95e7281e2438b77144d87a88e8090fa038fc0 100644
--- a/src/query/src/qAggMain.c
+++ b/src/query/src/qAggMain.c
@@ -3393,7 +3393,7 @@ enum {
 };
 
 static bool diff_function_setup(SQLFunctionCtx *pCtx) {
-  if (function_setup(pCtx)) {
+  if (!function_setup(pCtx)) {
     return false;
   }
   
@@ -4606,7 +4606,7 @@ static void rate_function_f(SQLFunctionCtx *pCtx, int32_t index) {
   
   pRateInfo->lastValue = v;
   pRateInfo->lastKey   = primaryKey[index];
-  
+
   SET_VAL(pCtx, 1, 1);
   
   // set has result flag
@@ -4630,7 +4630,7 @@ static void rate_func_copy(SQLFunctionCtx *pCtx) {
 static void rate_finalizer(SQLFunctionCtx *pCtx) {
   SResultRowCellInfo *pResInfo  = GET_RES_INFO(pCtx);
   SRateInfo   *pRateInfo = (SRateInfo *)GET_ROWCELL_INTERBUF(pResInfo);
-  
+
   if (pRateInfo->hasResult != DATA_SET_FLAG) {
     setNull(pCtx->pOutput, TSDB_DATA_TYPE_DOUBLE, sizeof(double));
     return;
@@ -5215,7 +5215,7 @@ SAggFunctionInfo aAggs[] = {{
                               "diff",
                               TSDB_FUNC_DIFF,
                               TSDB_FUNC_INVALID_ID,
-                              TSDB_FUNCSTATE_MO | TSDB_FUNCSTATE_NEED_TS,
+                              TSDB_FUNCSTATE_MO | TSDB_FUNCSTATE_STABLE | TSDB_FUNCSTATE_NEED_TS,
                               diff_function_setup,
                               diff_function,
                               diff_function_f,
diff --git a/src/query/src/qExecutor.c b/src/query/src/qExecutor.c
index 9e1534eb24b7c4495c57fd9f0f60b1bd7a20ac1e..7972649e25be1b601beb2873db51e1fe1c98e8dd 100644
--- a/src/query/src/qExecutor.c
+++ b/src/query/src/qExecutor.c
@@ -2652,7 +2652,7 @@ int32_t loadDataBlockOnDemand(SQueryRuntimeEnv* pRuntimeEnv, STableScanInfo* pTa
                                   pTableScanInfo->rowCellInfoOffset) != TSDB_CODE_SUCCESS) {
         longjmp(pRuntimeEnv->env, TSDB_CODE_QRY_OUT_OF_MEMORY);
       }
-    } else if (pQueryAttr->stableQuery && (!pQueryAttr->tsCompQuery)) { // stable aggregate, not interval aggregate or normal column aggregate
+    } else if (pQueryAttr->stableQuery && (!pQueryAttr->tsCompQuery) && (!pQueryAttr->diffQuery)) { // stable aggregate, not interval aggregate or normal column aggregate
       doSetTableGroupOutputBuf(pRuntimeEnv, pTableScanInfo->pResultRowInfo, pTableScanInfo->pCtx,
                                pTableScanInfo->rowCellInfoOffset, pTableScanInfo->numOfOutput,
                                pRuntimeEnv->current->groupIndex);
@@ -4273,6 +4273,12 @@ static SSDataBlock* doTableScanImpl(void* param, bool* newgroup) {
 
       pRuntimeEnv->current = *pTableQueryInfo;
       doTableQueryInfoTimeWindowCheck(pQueryAttr, *pTableQueryInfo);
+
+      if (pTableScanInfo->prevGroupId != -1 && pTableScanInfo->prevGroupId != (*pTableQueryInfo)->groupIndex) {
+        *newgroup = true;
+      }
+
+      pTableScanInfo->prevGroupId = (*pTableQueryInfo)->groupIndex;
     }
 
     // this function never returns error?
@@ -4419,6 +4425,7 @@ SOperatorInfo* createTableScanOperator(void* pTsdbQueryHandle, SQueryRuntimeEnv*
   pInfo->reverseTimes = 0;
   pInfo->order        = pRuntimeEnv->pQueryAttr->order.order;
   pInfo->current      = 0;
+//  pInfo->prevGroupId  = -1;
 
   SOperatorInfo* pOperator = calloc(1, sizeof(SOperatorInfo));
   pOperator->name         = "TableScanOperator";
@@ -4441,6 +4448,7 @@ SOperatorInfo* createTableSeqScanOperator(void* pTsdbQueryHandle, SQueryRuntimeE
   pInfo->reverseTimes     = 0;
   pInfo->order            = pRuntimeEnv->pQueryAttr->order.order;
   pInfo->current          = 0;
+  pInfo->prevGroupId      = -1;
 
   SOperatorInfo* pOperator = calloc(1, sizeof(SOperatorInfo));
   pOperator->name         = "TableSeqScanOperator";
@@ -4545,6 +4553,7 @@ SOperatorInfo* createDataBlocksOptScanInfo(void* pTsdbQueryHandle, SQueryRuntime
   pInfo->reverseTimes = reverseTime;
   pInfo->current      = 0;
   pInfo->order        = pRuntimeEnv->pQueryAttr->order.order;
+//  pInfo->prevGroupId  = -1;
 
   SOperatorInfo* pOptr = calloc(1, sizeof(SOperatorInfo));
   pOptr->name          = "DataBlocksOptimizedScanOperator";
@@ -4923,10 +4932,17 @@ static SSDataBlock* doArithmeticOperation(void* param, bool* newgroup) {
     }
 
     // Return result of the previous group in the firstly.
-    if (*newgroup && pRes->info.rows > 0) {
-      pArithInfo->existDataBlock = pBlock;
-      clearNumOfRes(pInfo->pCtx, pOperator->numOfOutput);
-      return pInfo->pRes;
+    if (*newgroup) {
+      if (pRes->info.rows > 0) {
+        pArithInfo->existDataBlock = pBlock;
+        clearNumOfRes(pInfo->pCtx, pOperator->numOfOutput);
+        return pInfo->pRes;
+      } else { // init output buffer for a new group data
+        for (int32_t j = 0; j < pOperator->numOfOutput; ++j) {
+          aAggs[pInfo->pCtx[j].functionId].xFinalize(&pInfo->pCtx[j]);
+        }
+        initCtxOutputBuffer(pInfo->pCtx, pOperator->numOfOutput);
+      }
     }
 
     STableQueryInfo* pTableQueryInfo = pRuntimeEnv->current;
@@ -7442,7 +7458,6 @@ int32_t doDumpQueryResult(SQInfo *pQInfo, char *data) {
     doCopyQueryResultToMsg(pQInfo, (int32_t)pRuntimeEnv->outputBuf->info.rows, data);
   }
 
-  pRuntimeEnv->resultInfo.total += pRuntimeEnv->outputBuf->info.rows;
   qDebug("QInfo:0x%"PRIx64" current numOfRes rows:%d, total:%" PRId64, pQInfo->qId,
          pRuntimeEnv->outputBuf->info.rows, pRuntimeEnv->resultInfo.total);
 
diff --git a/src/query/src/qPlan.c b/src/query/src/qPlan.c
index 24531c7f4e6e9486cb2ad388ec50fa422606de52..ee587a515dca39559bc6d061501d4e3397c0781a 100644
--- a/src/query/src/qPlan.c
+++ b/src/query/src/qPlan.c
@@ -531,7 +531,7 @@ SArray* createTableScanPlan(SQueryAttr* pQueryAttr) {
   } else {
     if (pQueryAttr->queryBlockDist) {
       op = OP_TableBlockInfoScan;
-    } else if (pQueryAttr->tsCompQuery || pQueryAttr->pointInterpQuery) {
+    } else if (pQueryAttr->tsCompQuery || pQueryAttr->pointInterpQuery || pQueryAttr->diffQuery) {
       op = OP_TableSeqScan;
     } else if (pQueryAttr->needReverseScan) {
       op = OP_DataBlocksOptScan;
@@ -605,7 +605,7 @@ SArray* createExecOperatorPlan(SQueryAttr* pQueryAttr) {
       taosArrayPush(plan, &op);
     }
   } else if (pQueryAttr->simpleAgg) {
-    if (pQueryAttr->stableQuery && !pQueryAttr->tsCompQuery) {
+    if (pQueryAttr->stableQuery && !pQueryAttr->tsCompQuery && !pQueryAttr->diffQuery) {
       op = OP_MultiTableAggregate;
     } else {
       op = OP_Aggregate;
diff --git a/src/query/src/queryMain.c b/src/query/src/queryMain.c
index f00d5ceb41aad443911036925ef92a6fc3fd4030..fa2eac66194314cff252f61339097628ba4c4f25 100644
--- a/src/query/src/queryMain.c
+++ b/src/query/src/queryMain.c
@@ -241,15 +241,16 @@ bool qTableQuery(qinfo_t qinfo, uint64_t *qId) {
 
   bool newgroup = false;
   pRuntimeEnv->outputBuf = pRuntimeEnv->proot->exec(pRuntimeEnv->proot, &newgroup);
+  pRuntimeEnv->resultInfo.total += GET_NUM_OF_RESULTS(pRuntimeEnv);
 
   if (isQueryKilled(pQInfo)) {
     qDebug("QInfo:0x%"PRIx64" query is killed", pQInfo->qId);
   } else if (GET_NUM_OF_RESULTS(pRuntimeEnv) == 0) {
-    qDebug("QInfo:0x%"PRIx64" over, %u tables queried, %"PRId64" rows are returned", pQInfo->qId, pRuntimeEnv->tableqinfoGroupInfo.numOfTables,
+    qDebug("QInfo:0x%"PRIx64" over, %u tables queried, total %"PRId64" rows returned", pQInfo->qId, pRuntimeEnv->tableqinfoGroupInfo.numOfTables,
            pRuntimeEnv->resultInfo.total);
   } else {
-    qDebug("QInfo:0x%"PRIx64" query paused, %d rows returned, numOfTotal:%" PRId64 " rows",
-           pQInfo->qId, GET_NUM_OF_RESULTS(pRuntimeEnv), pRuntimeEnv->resultInfo.total + GET_NUM_OF_RESULTS(pRuntimeEnv));
+    qDebug("QInfo:0x%"PRIx64" query paused, %d rows returned, total:%" PRId64 " rows", pQInfo->qId,
+        GET_NUM_OF_RESULTS(pRuntimeEnv), pRuntimeEnv->resultInfo.total);
   }
 
   return doBuildResCheck(pQInfo);