diff --git a/src/query/inc/queryExecutor.h b/src/query/inc/queryExecutor.h
index 3932650e1f0b2bcd7511dd8a98ba2be8baef36f2..03027329950ce1fa2dc0cc1b9659eb75cd52bb49 100644
--- a/src/query/inc/queryExecutor.h
+++ b/src/query/inc/queryExecutor.h
@@ -160,7 +160,7 @@ typedef struct SQueryRuntimeEnv {
   SQueryCostSummary  summary;
   bool               stableQuery;  // super table query or not
   void*              pQueryHandle;
-  void*              pSubQueryHandle; // another thread for
+  void*              pSecQueryHandle; // another thread for
   SDiskbasedResultBuf* pResultBuf;  // query result buffer based on blocked-wised disk file
 } SQueryRuntimeEnv;
 
diff --git a/src/query/src/queryExecutor.c b/src/query/src/queryExecutor.c
index 0f74cf1bebb5f5259b7270652b0ebf9c54c9d5ed..8015360919a829695f11df9ccb8b131343678036 100644
--- a/src/query/src/queryExecutor.c
+++ b/src/query/src/queryExecutor.c
@@ -1552,6 +1552,8 @@ static void teardownQueryRuntimeEnv(SQueryRuntimeEnv *pRuntimeEnv) {
 
   destroyResultBuf(pRuntimeEnv->pResultBuf);
   tsdbCleanupQueryHandle(pRuntimeEnv->pQueryHandle);
+  tsdbCleanupQueryHandle(pRuntimeEnv->pSecQueryHandle);
+  
   pRuntimeEnv->pTSBuf = tsBufDestory(pRuntimeEnv->pTSBuf);
 }
 
@@ -2565,7 +2567,7 @@ static int64_t doScanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
   dTrace("QInfo:%p query start, qrange:%" PRId64 "-%" PRId64 ", lastkey:%" PRId64 ", order:%d",
          GET_QINFO_ADDR(pRuntimeEnv), pQuery->window.skey, pQuery->window.ekey, pQuery->lastKey, pQuery->order.order);
 
-  tsdb_query_handle_t pQueryHandle = pRuntimeEnv->scanFlag == MASTER_SCAN? pRuntimeEnv->pQueryHandle:pRuntimeEnv->pSubQueryHandle;
+  tsdb_query_handle_t pQueryHandle = pRuntimeEnv->scanFlag == MASTER_SCAN? pRuntimeEnv->pQueryHandle:pRuntimeEnv->pSecQueryHandle;
   while (tsdbNextDataBlock(pQueryHandle)) {
     
     if (isQueryKilled(GET_QINFO_ADDR(pRuntimeEnv))) {
@@ -3557,7 +3559,10 @@ void scanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
       taosArrayPush(cols, &pQuery->colList[i]);
     }
   
-    pRuntimeEnv->pSubQueryHandle = tsdbQueryByTableId(pQInfo->tsdb, &cond, pQInfo->pTableIdList, cols);
+    if (pRuntimeEnv->pSecQueryHandle != NULL) {
+      pRuntimeEnv->pSecQueryHandle = tsdbQueryByTableId(pQInfo->tsdb, &cond, pQInfo->pTableIdList, cols);
+    }
+    
     taosArrayDestroy(cols);
   
     status = pQuery->status;
diff --git a/src/vnode/tsdb/src/tsdbRead.c b/src/vnode/tsdb/src/tsdbRead.c
index 966debda8d9117bc153d2aab979f36141a3f58ea..ee95199e5bf15d0d9a00f57a24351e33ffb4bf08 100644
--- a/src/vnode/tsdb/src/tsdbRead.c
+++ b/src/vnode/tsdb/src/tsdbRead.c
@@ -218,9 +218,31 @@ static bool hasMoreDataInCache(STsdbQueryHandle* pHandle) {
   if (pTable->mem == NULL && pTable->imem == NULL) {
     return false;
   }
+  
+  STableCheckInfo* pCheckInfo = taosArrayGet(pHandle->pTableCheckInfo, pHandle->activeIndex);
+  pTable = pCheckInfo->pTableObj;
+  
+  if (pCheckInfo->iter == NULL) {
+    pCheckInfo->iter = tSkipListCreateIter(pTable->mem->pData);
+    if (pCheckInfo->iter == NULL) {
+      return false;
+    }
+  }
+  
+  if (!tSkipListIterNext(pCheckInfo->iter)) {  // buffer is empty
+    return false;
+  }
+
+  SSkipListNode* node = tSkipListIterGet(pCheckInfo->iter);
+  if (node == NULL) {
+    return false;
+  }
 
+  SDataRow row = SL_GET_NODE_DATA(node);
+  pCheckInfo->lastKey = dataRowKey(row);  // first timestamp in buffer
+  
   // all data in mem are checked already.
-  if (pTableCheckInfo->lastKey > pTable->mem->keyLast) {
+  if (pTableCheckInfo->lastKey > pHandle->window.ekey) {
     return false;
   }
 
@@ -522,13 +544,15 @@ static int vnodeBinarySearchKey(char* pValue, int num, TSKEY key, int order) {
   int    numOfPoints;
   TSKEY* keyList;
 
+  assert(order == TSDB_ORDER_ASC || order == TSDB_ORDER_DESC);
+  
   if (num <= 0) return -1;
 
   keyList = (TSKEY*)pValue;
   firstPos = 0;
   lastPos = num - 1;
 
-  if (order == 0) {
+  if (order == TSDB_ORDER_DESC) {
     // find the first position which is smaller than the key
     while (1) {
       if (key >= keyList[lastPos]) return lastPos;
@@ -596,8 +620,8 @@ static void filterDataInDataBlock(STsdbQueryHandle* pQueryHandle, STableCheckInf
     pQueryHandle->realNumOfRows = cur->pos + 1;
     pCheckInfo->lastKey = blockInfo.window.ekey - 1;
   } else {
-    endPos =
-        vnodeBinarySearchKey(pCols->cols[0].pData, pCols->numOfPoints, pQueryHandle->window.ekey, pQueryHandle->order);
+    int32_t order = (pQueryHandle->order == TSDB_ORDER_ASC)? TSDB_ORDER_DESC:TSDB_ORDER_ASC;
+    endPos = vnodeBinarySearchKey(pCols->cols[0].pData, pCols->numOfPoints, pQueryHandle->window.ekey, order);
 
     if (QUERY_IS_ASC_QUERY(pQueryHandle->order)) {
       if (endPos < cur->pos) {
@@ -1042,7 +1066,7 @@ static int tsdbReadRowsFromCache(SSkipListIterator* pIter, TSKEY maxKey, int max
   int32_t numOfCols = taosArrayGetSize(pQueryHandle->pColumns);
   *skey = INT64_MIN;
 
-  while (tSkipListIterNext(pIter)) {
+  do/* (1) */{
     SSkipListNode* node = tSkipListIterGet(pIter);
     if (node == NULL) break;
 
@@ -1063,8 +1087,11 @@ static int tsdbReadRowsFromCache(SSkipListIterator* pIter, TSKEY maxKey, int max
     }
 
     numOfRows++;
-    if (numOfRows >= maxRowsToRead) break;
-  };
+    if (numOfRows >= maxRowsToRead) {
+      break;
+    }
+    
+  } while(tSkipListIterNext(pIter));
 
   return numOfRows;
 }
@@ -1107,10 +1134,8 @@ SDataBlockInfo tsdbRetrieveDataBlockInfo(tsdb_query_handle_t* pQueryHandle) {
 
     if (pTable->mem != NULL) {
       // create mem table iterator if it is not created yet
-      if (pCheckInfo->iter == NULL) {
-        pCheckInfo->iter = tSkipListCreateIter(pTable->mem->pData);
-      }
-      rows = tsdbReadRowsFromCache(pCheckInfo->iter, INT64_MAX, 2, &skey, &ekey, pHandle);
+      assert(pCheckInfo->iter != NULL);
+      rows = tsdbReadRowsFromCache(pCheckInfo->iter, pHandle->window.ekey, 2, &skey, &ekey, pHandle);
 
       // update the last key value
       pCheckInfo->lastKey = ekey + 1;