diff --git a/src/tsdb/src/tsdbRead.c b/src/tsdb/src/tsdbRead.c
index 5cb0dffd46d4fef05619eb47145acd0b5e4a0937..5b1afe3da8f9afc58163a26d4a1d1939f0069998 100644
--- a/src/tsdb/src/tsdbRead.c
+++ b/src/tsdb/src/tsdbRead.c
@@ -21,7 +21,7 @@
 #include "tcompare.h"
 #include "exception.h"
 
-#include "../../../query/inc/qast.h"  // todo move to common module
+#include "../../query/inc/qAst.h"  // todo move to common module
 #include "tlosertree.h"
 #include "tsdb.h"
 #include "tsdbMain.h"
@@ -331,7 +331,8 @@ static bool initTableMemIterator(STsdbQueryHandle* pHandle, STableCheckInfo* pCh
     tsdbDebug("%p uid:%" PRId64", tid:%d check data in mem from skey:%" PRId64 ", order:%d, %p", pHandle,
            pCheckInfo->tableId.uid, pCheckInfo->tableId.tid, key, order, pHandle->qinfo);
   } else {
-    tsdbDebug("%p uid:%" PRId64 ", tid:%d no data in mem", pHandle, pCheckInfo->tableId.uid, pCheckInfo->tableId.tid);
+    tsdbDebug("%p uid:%"PRId64", tid:%d no data in mem, %p", pHandle, pCheckInfo->tableId.uid, pCheckInfo->tableId.tid,
+        pHandle->qinfo);
   }
   
   if (!imemEmpty) {
@@ -343,7 +344,8 @@ static bool initTableMemIterator(STsdbQueryHandle* pHandle, STableCheckInfo* pCh
     tsdbDebug("%p uid:%" PRId64", tid:%d check data in imem from skey:%" PRId64 ", order:%d, %p", pHandle,
            pCheckInfo->tableId.uid, pCheckInfo->tableId.tid, key, order, pHandle->qinfo);
   } else {
-    tsdbDebug("%p uid:%"PRId64", tid:%d no data in imem", pHandle, pCheckInfo->tableId.uid, pCheckInfo->tableId.tid);
+    tsdbDebug("%p uid:%"PRId64", tid:%d no data in imem, %p", pHandle, pCheckInfo->tableId.uid, pCheckInfo->tableId.tid,
+        pHandle->qinfo);
   }
   
   return true;
@@ -354,7 +356,7 @@ static void destroyTableMemIterator(STableCheckInfo* pCheckInfo) {
   tSkipListDestroyIter(pCheckInfo->iiter);
 }
 
-SDataRow getSDataRowInTableMem(STableCheckInfo* pCheckInfo) {
+SDataRow getSDataRowInTableMem(STableCheckInfo* pCheckInfo, int32_t order) {
   SDataRow rmem = NULL, rimem = NULL;
   if (pCheckInfo->iter) {
     SSkipListNode* node = tSkipListIterGet(pCheckInfo->iter);
@@ -371,20 +373,35 @@ SDataRow getSDataRowInTableMem(STableCheckInfo* pCheckInfo) {
   }
 
   if (rmem != NULL && rimem != NULL) {
-    if (dataRowKey(rmem) < dataRowKey(rimem)) {
-      pCheckInfo->chosen = 0;
-      return rmem;
-    } else if (dataRowKey(rmem) == dataRowKey(rimem)) {
-      // data ts are duplicated, ignore the data in mem
+    TSKEY r1 = dataRowKey(rmem);
+    TSKEY r2 = dataRowKey(rimem);
+
+    if (r1 == r2) { // data ts are duplicated, ignore the data in mem
       tSkipListIterNext(pCheckInfo->iter);
       pCheckInfo->chosen = 1;
       return rimem;
     } else {
-      pCheckInfo->chosen = 1;
-      return rimem;
+      if (ASCENDING_TRAVERSE(order)) {
+        if (r1 < r2) {
+          pCheckInfo->chosen = 0;
+          return rmem;
+        } else {
+          pCheckInfo->chosen = 1;
+          return rimem;
+        }
+      } else {
+        if (r1 < r2) {
+          pCheckInfo->chosen = 1;
+          return rimem;
+        } else {
+          pCheckInfo->chosen = 0;
+          return rmem;
+        }
+      }
     }
   }
 
+  // at least one (rmem or rimem) is absent here
   if (rmem != NULL) {
     pCheckInfo->chosen = 0;
     return rmem;
@@ -398,7 +415,7 @@ SDataRow getSDataRowInTableMem(STableCheckInfo* pCheckInfo) {
   return NULL;
 }
 
-static bool moveToNextRow(STableCheckInfo* pCheckInfo) {
+static bool moveToNextRowInMem(STableCheckInfo* pCheckInfo) {
   bool hasNext = false;
   if (pCheckInfo->chosen == 0) {
     if (pCheckInfo->iter != NULL) {
@@ -412,19 +429,17 @@ static bool moveToNextRow(STableCheckInfo* pCheckInfo) {
     if (pCheckInfo->iiter != NULL) {
       return tSkipListIterGet(pCheckInfo->iiter) != NULL;
     }
-  } else {
-    if (pCheckInfo->chosen == 1) {
-      if (pCheckInfo->iiter != NULL) {
-        hasNext = tSkipListIterNext(pCheckInfo->iiter);
-      }
+  } else { //pCheckInfo->chosen == 1
+    if (pCheckInfo->iiter != NULL) {
+      hasNext = tSkipListIterNext(pCheckInfo->iiter);
+    }
 
-      if (hasNext) {
-        return hasNext;
-      }
+    if (hasNext) {
+      return hasNext;
+    }
 
-      if (pCheckInfo->iter != NULL) {
-        return tSkipListIterGet(pCheckInfo->iter) != NULL;
-      }
+    if (pCheckInfo->iter != NULL) {
+      return tSkipListIterGet(pCheckInfo->iter) != NULL;
     }
   }
 
@@ -445,7 +460,7 @@ static bool hasMoreDataInCache(STsdbQueryHandle* pHandle) {
     initTableMemIterator(pHandle, pCheckInfo);
   }
 
-  SDataRow row = getSDataRowInTableMem(pCheckInfo);
+  SDataRow row = getSDataRowInTableMem(pCheckInfo, pHandle->order);
   if (row == NULL) {
     return false;
   }
@@ -650,7 +665,7 @@ static void handleDataMergeIfNeeded(STsdbQueryHandle* pQueryHandle, SCompBlock*
   SDataBlockInfo binfo = GET_FILE_DATA_BLOCK_INFO(pCheckInfo, pBlock);
 
   /*bool hasData = */ initTableMemIterator(pQueryHandle, pCheckInfo);
-  SDataRow row = getSDataRowInTableMem(pCheckInfo);
+  SDataRow row = getSDataRowInTableMem(pCheckInfo, pQueryHandle->order);
 
   TSKEY key = (row != NULL)? dataRowKey(row):TSKEY_INITIAL_VAL;
   cur->pos = ASCENDING_TRAVERSE(pQueryHandle->order)? 0:(binfo.rows-1);
@@ -1033,7 +1048,7 @@ static void doMergeTwoLevelData(STsdbQueryHandle* pQueryHandle, STableCheckInfo*
   } else if (pCheckInfo->iter != NULL || pCheckInfo->iiter != NULL) {
     SSkipListNode* node = NULL;
     do {
-      SDataRow row = getSDataRowInTableMem(pCheckInfo);
+      SDataRow row = getSDataRowInTableMem(pCheckInfo, pQueryHandle->order);
       if (row == NULL) {
         break;
       }
@@ -1061,9 +1076,9 @@ static void doMergeTwoLevelData(STsdbQueryHandle* pQueryHandle, STableCheckInfo*
         cur->lastKey  = key + step;
         cur->mixBlock = true;
 
-        moveToNextRow(pCheckInfo);
+        moveToNextRowInMem(pCheckInfo);
       } else if (key == tsArray[pos]) {  // data in buffer has the same timestamp of data in file block, ignore it
-        moveToNextRow(pCheckInfo);
+        moveToNextRowInMem(pCheckInfo);
       } else if ((key > tsArray[pos] && ASCENDING_TRAVERSE(pQueryHandle->order)) ||
                   (key < tsArray[pos] && !ASCENDING_TRAVERSE(pQueryHandle->order))) {
         if (cur->win.skey == TSKEY_INITIAL_VAL) {
@@ -1072,7 +1087,7 @@ static void doMergeTwoLevelData(STsdbQueryHandle* pQueryHandle, STableCheckInfo*
 
         int32_t end = doBinarySearchKey(pCols->cols[0].pData, pCols->numOfRows, key, order);
         if (tsArray[end] == key) { // the value of key in cache equals to the end timestamp value, ignore it
-          moveToNextRow(pCheckInfo);
+          moveToNextRowInMem(pCheckInfo);
         }
         
         int32_t start = -1;
@@ -1754,7 +1769,7 @@ static int tsdbReadRowsFromCache(STableCheckInfo* pCheckInfo, TSKEY maxKey, int
   STable* pTable = pCheckInfo->pTableObj;
 
   do {
-    SDataRow row = getSDataRowInTableMem(pCheckInfo);
+    SDataRow row = getSDataRowInTableMem(pCheckInfo, pQueryHandle->order);
     if (row == NULL) {
       break;
     }
@@ -1775,11 +1790,11 @@ static int tsdbReadRowsFromCache(STableCheckInfo* pCheckInfo, TSKEY maxKey, int
     copyOneRowFromMem(pQueryHandle, maxRowsToRead, numOfRows, row, pMeta, numOfCols, pTable);
 
     if (++numOfRows >= maxRowsToRead) {
-      moveToNextRow(pCheckInfo);
+      moveToNextRowInMem(pCheckInfo);
       break;
     }
     
-  } while(moveToNextRow(pCheckInfo));
+  } while(moveToNextRowInMem(pCheckInfo));
 
   assert(numOfRows <= maxRowsToRead);