diff --git a/src/common/src/tdataformat.c b/src/common/src/tdataformat.c
index aa60803dac740157e1a9f5229e524bca8401c4cd..61378c79c4b5c44ffa11ae9132aa6f8b89ab5f71 100644
--- a/src/common/src/tdataformat.c
+++ b/src/common/src/tdataformat.c
@@ -448,6 +448,7 @@ static void tdAppendDataRowToDataCol(SDataRow row, STSchema *pSchema, SDataCols
   int dcol = 0;
 
   while (dcol < pCols->numOfCols) {
+    bool setCol = 0;
     SDataCol *pDataCol = &(pCols->cols[dcol]);
     if (rcol >= schemaNCols(pSchema)) {
       dataColAppendVal(pDataCol, getNullValue(pDataCol->type), pCols->numOfRows, pCols->maxPoints);
@@ -458,13 +459,14 @@ static void tdAppendDataRowToDataCol(SDataRow row, STSchema *pSchema, SDataCols
     STColumn *pRowCol = schemaColAt(pSchema, rcol);
     if (pRowCol->colId == pDataCol->colId) {
       void *value = tdGetRowDataOfCol(row, pRowCol->type, pRowCol->offset + TD_DATA_ROW_HEAD_SIZE);
+      if(!isNull(value, pDataCol->type)) setCol = 1;
       dataColAppendVal(pDataCol, value, pCols->numOfRows, pCols->maxPoints);
       dcol++;
       rcol++;
     } else if (pRowCol->colId < pDataCol->colId) {
       rcol++;
     } else {
-      if(forceSetNull) {
+      if(forceSetNull || setCol) {
         dataColAppendVal(pDataCol, getNullValue(pDataCol->type), pCols->numOfRows, pCols->maxPoints);
       }
       dcol++;
@@ -482,6 +484,7 @@ static void tdAppendKvRowToDataCol(SKVRow row, STSchema *pSchema, SDataCols *pCo
   int nRowCols = kvRowNCols(row);
 
   while (dcol < pCols->numOfCols) {
+    bool setCol = 0;
     SDataCol *pDataCol = &(pCols->cols[dcol]);
     if (rcol >= nRowCols || rcol >= schemaNCols(pSchema)) {
       dataColAppendVal(pDataCol, getNullValue(pDataCol->type), pCols->numOfRows, pCols->maxPoints);
@@ -493,13 +496,14 @@ static void tdAppendKvRowToDataCol(SKVRow row, STSchema *pSchema, SDataCols *pCo
 
     if (colIdx->colId == pDataCol->colId) {
       void *value = tdGetKvRowDataOfCol(row, colIdx->offset);
+      if(!isNull(value, pDataCol->type)) setCol = 1;
       dataColAppendVal(pDataCol, value, pCols->numOfRows, pCols->maxPoints);
       ++dcol;
       ++rcol;
     } else if (colIdx->colId < pDataCol->colId) {
       ++rcol;
     } else {
-      if (forceSetNull) {
+      if(forceSetNull || setCol) {
         dataColAppendVal(pDataCol, getNullValue(pDataCol->type), pCols->numOfRows, pCols->maxPoints);
       }
       ++dcol;
@@ -518,7 +522,6 @@ void tdAppendMemRowToDataCol(SMemRow row, STSchema *pSchema, SDataCols *pCols, b
   }
 }
 
-//TODO: refactor this function to eliminate additional memory copy
 int tdMergeDataCols(SDataCols *target, SDataCols *source, int rowsToMerge, int *pOffset, bool forceSetNull) {
   ASSERT(rowsToMerge > 0 && rowsToMerge <= source->numOfRows);
   ASSERT(target->numOfCols == source->numOfCols);
@@ -534,7 +537,7 @@ int tdMergeDataCols(SDataCols *target, SDataCols *source, int rowsToMerge, int *
     ASSERT(target->numOfRows + rowsToMerge <= target->maxPoints);
     for (int i = 0; i < rowsToMerge; i++) {
       for (int j = 0; j < source->numOfCols; j++) {
-        if (source->cols[j].len > 0) {
+        if (source->cols[j].len > 0 || target->cols[j].len > 0) {
           dataColAppendVal(target->cols + j, tdGetColDataOfRow(source->cols + j, i + (*pOffset)), target->numOfRows,
                            target->maxPoints);
         }
@@ -578,7 +581,7 @@ static void tdMergeTwoDataCols(SDataCols *target, SDataCols *src1, int *iter1, i
     if (key1 < key2) {
       for (int i = 0; i < src1->numOfCols; i++) {
         ASSERT(target->cols[i].type == src1->cols[i].type);
-        if (src1->cols[i].len > 0) {
+        if (src1->cols[i].len > 0 || target->cols[i].len > 0) {
           dataColAppendVal(&(target->cols[i]), tdGetColDataOfRow(src1->cols + i, *iter1), target->numOfRows,
                            target->maxPoints);
         }
@@ -596,6 +599,8 @@ static void tdMergeTwoDataCols(SDataCols *target, SDataCols *src1, int *iter1, i
           } else if(!forceSetNull && key1 == key2 && src1->cols[i].len > 0) {
             dataColAppendVal(&(target->cols[i]), tdGetColDataOfRow(src1->cols + i, *iter1), target->numOfRows,
                              target->maxPoints);
+          } else if(target->cols[i].len > 0) {
+            dataColSetNullAt(&target->cols[i], target->numOfRows);
           }
         }
         target->numOfRows++;
diff --git a/src/tsdb/src/tsdbCommit.c b/src/tsdb/src/tsdbCommit.c
index 15fc3cc47d663aa6f2fb8910ebbadc03861418c7..03110487807076bf8ac2ac7026ffdb828ea4c7c6 100644
--- a/src/tsdb/src/tsdbCommit.c
+++ b/src/tsdb/src/tsdbCommit.c
@@ -1418,13 +1418,11 @@ static void tsdbLoadAndMergeFromCache(SDataCols *pDataCols, int *iter, SCommitIt
 
   while (true) {
     key1 = (*iter >= pDataCols->numOfRows) ? INT64_MAX : dataColsKeyAt(pDataCols, *iter);
-    bool isRowDel = false;
     SMemRow row = tsdbNextIterRow(pCommitIter->pIter);
     if (row == NULL || memRowKey(row) > maxKey) {
       key2 = INT64_MAX;
     } else {
       key2 = memRowKey(row);
-      isRowDel = memRowDeleted(row);
     }
 
     if (key1 == INT64_MAX && key2 == INT64_MAX) break;
@@ -1439,36 +1437,33 @@ static void tsdbLoadAndMergeFromCache(SDataCols *pDataCols, int *iter, SCommitIt
       pTarget->numOfRows++;
       (*iter)++;
     } else if (key1 > key2) {
-      if (!isRowDel) {
-        if (pSchema == NULL || schemaVersion(pSchema) != memRowVersion(row)) {
-          pSchema = tsdbGetTableSchemaImpl(pCommitIter->pTable, false, false, memRowVersion(row));
-          ASSERT(pSchema != NULL);
-        }
-
-        tdAppendMemRowToDataCol(row, pSchema, pTarget, true);
+      if (pSchema == NULL || schemaVersion(pSchema) != memRowVersion(row)) {
+        pSchema = tsdbGetTableSchemaImpl(pCommitIter->pTable, false, false, memRowVersion(row));
+        ASSERT(pSchema != NULL);
       }
 
+      tdAppendMemRowToDataCol(row, pSchema, pTarget, true);
+
       tSkipListIterNext(pCommitIter->pIter);
     } else {
-      if (update) {
-        if (!isRowDel) {
-          if (pSchema == NULL || schemaVersion(pSchema) != memRowVersion(row)) {
-            pSchema = tsdbGetTableSchemaImpl(pCommitIter->pTable, false, false, memRowVersion(row));
-            ASSERT(pSchema != NULL);
-          }
-
-          tdAppendMemRowToDataCol(row, pSchema, pTarget, update == TD_ROW_OVERWRITE_UPDATE);
-        }
-      } else {
-        ASSERT(!isRowDel);
-
+      if (update != TD_ROW_OVERWRITE_UPDATE) {
+        //copy disk data
         for (int i = 0; i < pDataCols->numOfCols; i++) {
           //TODO: dataColAppendVal may fail
           dataColAppendVal(pTarget->cols + i, tdGetColDataOfRow(pDataCols->cols + i, *iter), pTarget->numOfRows,
                            pTarget->maxPoints);
         }
 
-        pTarget->numOfRows++;
+        if(update == TD_ROW_DISCARD_UPDATE) pTarget->numOfRows++;
+      }
+      if (update != TD_ROW_DISCARD_UPDATE) {
+        //copy mem data
+        if (pSchema == NULL || schemaVersion(pSchema) != memRowVersion(row)) {
+          pSchema = tsdbGetTableSchemaImpl(pCommitIter->pTable, false, false, memRowVersion(row));
+          ASSERT(pSchema != NULL);
+        }
+
+        tdAppendMemRowToDataCol(row, pSchema, pTarget, update == TD_ROW_OVERWRITE_UPDATE);
       }
       (*iter)++;
       tSkipListIterNext(pCommitIter->pIter);