diff --git a/source/dnode/vnode/src/tsdb/tsdbRead.c b/source/dnode/vnode/src/tsdb/tsdbRead.c
index ec4b438b2b2a7951528d0b972863efd27960a9ff..5dd5ced72d1eeda1948ea1b4794a3a3da462d145 100644
--- a/source/dnode/vnode/src/tsdb/tsdbRead.c
+++ b/source/dnode/vnode/src/tsdb/tsdbRead.c
@@ -147,7 +147,7 @@ struct STsdbReader {
 static SFileDataBlockInfo* getCurrentBlockInfo(SDataBlockIter* pBlockIter);
 static int buildDataBlockFromBufImpl(STableBlockScanInfo* pBlockScanInfo, TSDBKEY maxKey, int32_t capacity, STsdbReader* pReader);
 static TSDBROW* getValidRow(STbDataIter* pIter, bool* hasVal, STsdbReader* pReader);
-static int32_t doLoadRowsOfIdenticalTsInFileBlock(SBlockData* pBlockData, STableBlockScanInfo* pScanInfo, STsdbReader* pReader, SRowMerger* pMerger);
+static int32_t doMergeRowsInFileBlocks(SBlockData* pBlockData, STableBlockScanInfo* pScanInfo, STsdbReader* pReader, SRowMerger* pMerger);
 static int32_t doLoadRowsOfIdenticalTsInBuf(STbDataIter *pIter, bool* hasVal, int64_t ts, SRowMerger* pMerger, STsdbReader* pReader);
 static int32_t doAppendOneRow(SSDataBlock* pBlock, STsdbReader* pReader, STSRow* pTSRow);
 static void    setComposedBlockFlag(STsdbReader* pReader, bool composed);
@@ -829,7 +829,7 @@ static void setBlockAllDumped(SFileBlockDumpInfo* pDumpInfo, SBlock* pBlock, int
 
 static void doCopyColVal(SColumnInfoData* pColInfoData, int32_t rowIndex, int32_t colIndex, SColVal* pColVal, SBlockLoadSuppInfo* pSup) {
   if (IS_VAR_DATA_TYPE(pColVal->type)) {
-    if (pColVal->isNull) {
+    if (pColVal->isNull || pColVal->isNone) {
       colDataAppendNULL(pColInfoData, rowIndex);
     } else {
       varDataSetLen(pSup->buildBuf[colIndex], pColVal->value.nData);
@@ -2096,58 +2096,83 @@ static int32_t buildDataBlockFromBuf(STsdbReader* pReader, STableBlockScanInfo*
   return code;
 }
 
-static int32_t doMergeBufFileRows(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo, TSDBROW* pRow,
-                                  STSRow* pTSRow, STbDataIter* pIter, bool* hasVal, int64_t key,
-                                  SFileDataBlockInfo* pFBlock, SBlock* pBlock) {
+static int32_t doMergeBufAndFileRows(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo, TSDBROW* pRow,
+                                  STSRow* pTSRow, STbDataIter* pIter, bool* hasVal, int64_t key) {
   SRowMerger          merge = {0};
   SBlockData*         pBlockData = &pReader->status.fileBlockData;
   SFileBlockDumpInfo* pDumpInfo = &pReader->status.fBlockDumpInfo;
 
   TSDBKEY k = TSDBROW_KEY(pRow);
-  if (key <= k.ts) {
-    TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
-    tRowMergerInit(&merge, &fRow, pReader->pSchema);
+  TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
 
-    doLoadRowsOfIdenticalTsInFileBlock(pBlockData, pBlockScanInfo, pReader, &merge);
+  // ascending order traverse
+  if (ASCENDING_TRAVERSE(pReader->order)) {
+    if (key < k.ts) {
+      tRowMergerInit(&merge, &fRow, pReader->pSchema);
+
+      doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+      tRowMergerGetRow(&merge, &pTSRow);
+    } else if (k.ts < key) {  // k.ts < key
+      doMergeMultiRows(pRow, pBlockScanInfo->uid, pIter, hasVal, &pTSRow, pReader);
+    } else {  // k.ts == key, ascending order: file block ----> imem rows -----> mem rows
+      tRowMergerInit(&merge, &fRow, pReader->pSchema);
+      doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
 
-    if (k.ts == key) {
       tRowMerge(&merge, pRow);
       doLoadRowsOfIdenticalTsInBuf(pIter, hasVal, k.ts, &merge, pReader);
+
+      tRowMergerGetRow(&merge, &pTSRow);
     }
+  } else {  // descending order scan
+    if (key < k.ts) {
+      doMergeMultiRows(pRow, pBlockScanInfo->uid, pIter, hasVal, &pTSRow, pReader);
+    } else if (k.ts < key) {
+      tRowMergerInit(&merge, &fRow, pReader->pSchema);
 
-    tRowMergerGetRow(&merge, &pTSRow);
-  } else {  // k.ts < key
-    doMergeMultiRows(pRow, pBlockScanInfo->uid, pIter, hasVal, &pTSRow, pReader);
+      doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+      tRowMergerGetRow(&merge, &pTSRow);
+    } else {  // descending order: mem rows -----> imem rows ------> file block
+      updateSchema(pRow, pBlockScanInfo->uid, pReader);
+
+      tRowMergerInit(&merge, pRow, pReader->pSchema);
+      doLoadRowsOfIdenticalTsInBuf(pIter, hasVal, k.ts, &merge, pReader);
+
+      tRowMerge(&merge, &fRow);
+      doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+
+      tRowMergerGetRow(&merge, &pTSRow);
+    }
   }
 
+  tRowMergerClear(&merge);
   doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
   return TSDB_CODE_SUCCESS;
 }
 
-static int32_t buildComposedDataBlockImpl(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo) {
+static int32_t doMergeThreeLevelRows(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo) {
+  SRowMerger merge = {0};
+  STSRow*    pTSRow = NULL;
+
   SFileBlockDumpInfo* pDumpInfo = &pReader->status.fBlockDumpInfo;
   SBlockData*         pBlockData = &pReader->status.fileBlockData;
 
-  SFileDataBlockInfo* pFBlock = getCurrentBlockInfo(&pReader->status.blockIter);
-  SBlock*             pBlock = taosArrayGet(pBlockScanInfo->pBlockList, pFBlock->tbBlockIdx);
-
-  SRowMerger merge = {0};
-  STSRow*    pTSRow = NULL;
+  TSDBROW* pRow  = getValidRow(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, pReader);
+  TSDBROW* piRow = getValidRow(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, pReader);
 
   int64_t  key = pBlockData->aTSKEY[pDumpInfo->rowIndex];
-  TSDBROW* pRow = getValidRow(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, pReader);
-  TSDBROW* piRow = getValidRow(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, pReader);
 
-  if (pBlockScanInfo->memHasVal && pBlockScanInfo->imemHasVal) {
-    TSDBKEY k = TSDBROW_KEY(pRow);
-    TSDBKEY ik = TSDBROW_KEY(piRow);
+  uint64_t uid = pBlockScanInfo->uid;
 
+  TSDBKEY k = TSDBROW_KEY(pRow);
+  TSDBKEY ik = TSDBROW_KEY(piRow);
+
+  if (ASCENDING_TRAVERSE(pReader->order)) {
     // [1&2] key <= [k.ts && ik.ts]
     if (key <= k.ts && key <= ik.ts) {
       TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
       tRowMergerInit(&merge, &fRow, pReader->pSchema);
 
-      doLoadRowsOfIdenticalTsInFileBlock(pBlockData, pBlockScanInfo, pReader, &merge);
+      doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
 
       if (ik.ts == key) {
         tRowMerge(&merge, piRow);
@@ -2161,12 +2186,14 @@ static int32_t buildComposedDataBlockImpl(STsdbReader* pReader, STableBlockScanI
 
       tRowMergerGetRow(&merge, &pTSRow);
       doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+      return TSDB_CODE_SUCCESS;
     } else {  // key > ik.ts || key > k.ts
+      ASSERT(key != ik.ts);
+
       // [3] ik.ts < key <= k.ts
       // [4] ik.ts < k.ts <= key
       if (ik.ts < k.ts) {
-        doMergeMultiRows(piRow, pBlockScanInfo->uid, pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, &pTSRow,
-                         pReader);
+        doMergeMultiRows(piRow, uid, pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, &pTSRow, pReader);
         doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
         return TSDB_CODE_SUCCESS;
       }
@@ -2174,39 +2201,116 @@ static int32_t buildComposedDataBlockImpl(STsdbReader* pReader, STableBlockScanI
       // [5] k.ts < key   <= ik.ts
       // [6] k.ts < ik.ts <= key
       if (k.ts < ik.ts) {
-        doMergeMultiRows(pRow, pBlockScanInfo->uid, pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, &pTSRow,
-                         pReader);
+        doMergeMultiRows(pRow, uid, pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, &pTSRow, pReader);
         doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
         return TSDB_CODE_SUCCESS;
       }
 
       // [7] k.ts == ik.ts < key
       if (k.ts == ik.ts) {
+        ASSERT(key > ik.ts && key > k.ts);
+
         doMergeMemIMemRows(pRow, piRow, pBlockScanInfo, pReader, &pTSRow);
         doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
         return TSDB_CODE_SUCCESS;
       }
     }
+  } else {  // descending order scan
+    // [1/2] k.ts >= ik.ts && k.ts >= key
+    if (k.ts >= ik.ts && k.ts >= key) {
+      updateSchema(pRow, uid, pReader);
+
+      tRowMergerInit(&merge, pRow, pReader->pSchema);
+      doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, key, &merge, pReader);
+
+      if (ik.ts == k.ts) {
+        tRowMerge(&merge, piRow);
+        doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, key, &merge, pReader);
+      }
+
+      if (k.ts == key) {
+        TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
+        tRowMerge(&merge, &fRow);
+        doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+      }
+
+      tRowMergerGetRow(&merge, &pTSRow);
+      doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+      return TSDB_CODE_SUCCESS;
+    } else {
+      ASSERT(ik.ts != k.ts);   // this case has been included in the previous if branch
+
+      // [3] ik.ts > k.ts >= Key
+      // [4] ik.ts > key >= k.ts
+      if (ik.ts > key) {
+        doMergeMultiRows(piRow, uid, pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, &pTSRow, pReader);
+        doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+        return TSDB_CODE_SUCCESS;
+      }
+
+      // [5] key > ik.ts > k.ts
+      // [6] key > k.ts > ik.ts
+      if (key > ik.ts) {
+        TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
+        tRowMergerInit(&merge, &fRow, pReader->pSchema);
+
+        doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+        tRowMergerGetRow(&merge, &pTSRow);
+        doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+        return TSDB_CODE_SUCCESS;
+      }
+
+      //[7] key = ik.ts > k.ts
+      if (key == ik.ts) {
+        doMergeMultiRows(piRow, uid, pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, &pTSRow, pReader);
+
+        TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
+        tRowMerge(&merge, &fRow);
+        doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
+        tRowMergerGetRow(&merge, &pTSRow);
+        doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+        return TSDB_CODE_SUCCESS;
+      }
+    }
+  }
+
+  ASSERT(0);
+}
+
+static int32_t buildComposedDataBlockImpl(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo) {
+  SFileBlockDumpInfo* pDumpInfo = &pReader->status.fBlockDumpInfo;
+  SBlockData*         pBlockData = &pReader->status.fileBlockData;
+
+  SRowMerger merge = {0};
+  STSRow*    pTSRow = NULL;
+
+  int64_t  key = pBlockData->aTSKEY[pDumpInfo->rowIndex];
+  TSDBROW* pRow = getValidRow(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, pReader);
+  TSDBROW* piRow = getValidRow(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, pReader);
+
+  if (pBlockScanInfo->memHasVal && pBlockScanInfo->imemHasVal) {
+    return doMergeThreeLevelRows(pReader, pBlockScanInfo);
   } else {
+    // imem + file
     if (pBlockScanInfo->imemHasVal) {
-      return doMergeBufFileRows(pReader, pBlockScanInfo, piRow, pTSRow, pBlockScanInfo->iiter,
-                                &pBlockScanInfo->imemHasVal, key, pFBlock, pBlock);
+      return doMergeBufAndFileRows(pReader, pBlockScanInfo, piRow, pTSRow, pBlockScanInfo->iiter,
+                                &pBlockScanInfo->imemHasVal, key);
     }
 
-    if (pBlockScanInfo->memHasVal) {  // pBlockScanInfo->memHasVal != NULL
-      return doMergeBufFileRows(pReader, pBlockScanInfo, pRow, pTSRow, pBlockScanInfo->iter, &pBlockScanInfo->memHasVal,
-                                key, pFBlock, pBlock);
+    // mem + file
+    if (pBlockScanInfo->memHasVal) {
+      return doMergeBufAndFileRows(pReader, pBlockScanInfo, pRow, pTSRow, pBlockScanInfo->iter, &pBlockScanInfo->memHasVal,
+                                key);
     }
 
-    // imem & mem are all empty
+    // imem & mem are all empty, only file exist
     TSDBROW fRow = tsdbRowFromBlockData(pBlockData, pDumpInfo->rowIndex);
     tRowMergerInit(&merge, &fRow, pReader->pSchema);
-    doLoadRowsOfIdenticalTsInFileBlock(pBlockData, pBlockScanInfo, pReader, &merge);
+    doMergeRowsInFileBlocks(pBlockData, pBlockScanInfo, pReader, &merge);
     tRowMergerGetRow(&merge, &pTSRow);
     doAppendOneRow(pReader->pResBlock, pReader, pTSRow);
+    return TSDB_CODE_SUCCESS;
   }
-
-  return TSDB_CODE_SUCCESS;
 }
 
 static int32_t buildComposedDataBlock(STsdbReader* pReader, STableBlockScanInfo* pBlockScanInfo) {
@@ -2671,39 +2775,31 @@ static int32_t checkForNeighborFileBlock(STsdbReader* pReader, STableBlockScanIn
   return TSDB_CODE_SUCCESS;
 }
 
-int32_t doLoadRowsOfIdenticalTsInFileBlock(SBlockData* pBlockData, STableBlockScanInfo* pScanInfo, STsdbReader* pReader, SRowMerger* pMerger) {
+int32_t doMergeRowsInFileBlocks(SBlockData* pBlockData, STableBlockScanInfo* pScanInfo, STsdbReader* pReader, SRowMerger* pMerger) {
   SFileBlockDumpInfo* pDumpInfo = &pReader->status.fBlockDumpInfo;
 
   bool    asc = ASCENDING_TRAVERSE(pReader->order);
   int64_t key = pBlockData->aTSKEY[pDumpInfo->rowIndex];
   int32_t step = asc ? 1 : -1;
 
-  if (asc) {
-    pDumpInfo->rowIndex += step;
-    if (pDumpInfo->rowIndex <= pBlockData->nRow - 1) {
-      pDumpInfo->rowIndex = doMergeRowsInFileBlockImpl(pBlockData, pDumpInfo->rowIndex, key, pMerger, &pReader->verRange, step);
-    }
+  pDumpInfo->rowIndex += step;
+  if (pDumpInfo->rowIndex <= pBlockData->nRow - 1) {
+    pDumpInfo->rowIndex =
+        doMergeRowsInFileBlockImpl(pBlockData, pDumpInfo->rowIndex, key, pMerger, &pReader->verRange, step);
+  }
 
-    // all rows are consumed, let's try next file block
-    if (pDumpInfo->rowIndex >= pBlockData->nRow && asc) {
-      while (1) {
-        CHECK_FILEBLOCK_STATE st;
+  // all rows are consumed, let's try next file block
+  if ((pDumpInfo->rowIndex >= pBlockData->nRow && asc) || (pDumpInfo->rowIndex < 0 && !asc)) {
+    while (1) {
+      CHECK_FILEBLOCK_STATE st;
 
-        SFileDataBlockInfo* pFileBlockInfo = getCurrentBlockInfo(&pReader->status.blockIter);
-        SBlock* pCurrentBlock = taosArrayGet(pScanInfo->pBlockList, pFileBlockInfo->tbBlockIdx);
-        checkForNeighborFileBlock(pReader, pScanInfo, pCurrentBlock, pFileBlockInfo, pMerger, key, &st);
-        if (st == CHECK_FILEBLOCK_QUIT)  {
-          break;
-        }
+      SFileDataBlockInfo* pFileBlockInfo = getCurrentBlockInfo(&pReader->status.blockIter);
+      SBlock*             pCurrentBlock = taosArrayGet(pScanInfo->pBlockList, pFileBlockInfo->tbBlockIdx);
+      checkForNeighborFileBlock(pReader, pScanInfo, pCurrentBlock, pFileBlockInfo, pMerger, key, &st);
+      if (st == CHECK_FILEBLOCK_QUIT) {
+        break;
       }
     }
-  } else {  // last row of current block, check if current block is overlapped with previous neighbor block
-    pDumpInfo->rowIndex += step;
-    //      bool overlap = overlapWithNeighborBlock(pFBlock, pBlock, pScanInfo);
-    //      if (overlap) {  // load next block
-    //        ASSERT(0);
-    //      }
-    //    }
   }
 
   return TSDB_CODE_SUCCESS;
@@ -2736,15 +2832,24 @@ void doMergeMemIMemRows(TSDBROW* pRow, TSDBROW* piRow, STableBlockScanInfo *pBlo
 
   TSDBKEY k = TSDBROW_KEY(pRow);
   TSDBKEY ik = TSDBROW_KEY(piRow);
-  ASSERT(k.ts == ik.ts);
 
-  updateSchema(piRow, pBlockScanInfo->uid, pReader);
+  if (ASCENDING_TRAVERSE(pReader->order)) {  // ascending order imem --> mem
+    updateSchema(piRow, pBlockScanInfo->uid, pReader);
+
+    tRowMergerInit(&merge, piRow, pReader->pSchema);
+    doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, ik.ts, &merge, pReader);
 
-  tRowMergerInit(&merge, piRow, pReader->pSchema);
-  doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, ik.ts, &merge, pReader);
+    tRowMerge(&merge, pRow);
+    doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, k.ts, &merge, pReader);
+  } else {
+    updateSchema(pRow, pBlockScanInfo->uid, pReader);
 
-  tRowMerge(&merge, pRow);
-  doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, k.ts, &merge, pReader);
+    tRowMergerInit(&merge, pRow, pReader->pSchema);
+    doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iiter, &pBlockScanInfo->memHasVal, ik.ts, &merge, pReader);
+
+    tRowMerge(&merge, piRow);
+    doLoadRowsOfIdenticalTsInBuf(pBlockScanInfo->iter, &pBlockScanInfo->imemHasVal, k.ts, &merge, pReader);
+  }
 
   tRowMergerGetRow(&merge, pTSRow);
 }
@@ -2753,20 +2858,19 @@ int32_t tsdbGetNextRowInMem(STableBlockScanInfo* pBlockScanInfo, STsdbReader* pR
   TSDBROW* pRow  = getValidRow(pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, pReader);
   TSDBROW* piRow = getValidRow(pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, pReader);
 
-  TSDBKEY k  = {.ts = TSKEY_INITIAL_VAL};
-  TSDBKEY ik = {.ts = TSKEY_INITIAL_VAL};
-
   if (pBlockScanInfo->memHasVal && pBlockScanInfo->imemHasVal) {
-    k = TSDBROW_KEY(pRow);
-    ik = TSDBROW_KEY(piRow);
+    TSDBKEY k  = TSDBROW_KEY(pRow);
+    TSDBKEY ik = TSDBROW_KEY(piRow);
 
-    if (ik.ts <= k.ts) {
-      doMergeMemIMemRows(pRow, piRow, pBlockScanInfo, pReader, pTSRow);
-      return TSDB_CODE_SUCCESS;
-    } else {  // k.ts < ik.ts
+    if (ik.ts < k.ts) {  // ik.ts < k.ts
+      doMergeMultiRows(piRow, pBlockScanInfo->uid, pBlockScanInfo->iiter, &pBlockScanInfo->imemHasVal, pTSRow, pReader);
+    } else if (k.ts < ik.ts) {
       doMergeMultiRows(piRow, pBlockScanInfo->uid, pBlockScanInfo->iter, &pBlockScanInfo->memHasVal, pTSRow, pReader);
-      return TSDB_CODE_SUCCESS;
+    } else {  // ik.ts == k.ts
+      doMergeMemIMemRows(pRow, piRow, pBlockScanInfo, pReader, pTSRow);
     }
+
+    return TSDB_CODE_SUCCESS;
   }
 
   if (pBlockScanInfo->memHasVal) {