diff --git a/source/dnode/vnode/src/tsdb/tsdbCache.c b/source/dnode/vnode/src/tsdb/tsdbCache.c
index 4b26697464..bba1d9f23a 100644
--- a/source/dnode/vnode/src/tsdb/tsdbCache.c
+++ b/source/dnode/vnode/src/tsdb/tsdbCache.c
@@ -452,9 +452,11 @@ static SLastCol *tsdbCacheLookup(STsdb *pTsdb, tb_uid_t uid, int16_t cid, int8_t
 static void reallocVarData(SColVal *pColVal) {
   if (IS_VAR_DATA_TYPE(pColVal->type)) {
     uint8_t *pVal = pColVal->value.pData;
-    pColVal->value.pData = taosMemoryMalloc(pColVal->value.nData);
-    if (pColVal->value.nData) {
+    if (pColVal->value.nData > 0) {
+      pColVal->value.pData = taosMemoryMalloc(pColVal->value.nData);
       memcpy(pColVal->value.pData, pVal, pColVal->value.nData);
+    } else {
+      pColVal->value.pData = NULL;
     }
   }
 }
@@ -2748,14 +2750,16 @@ static int32_t mergeLastCid(tb_uid_t uid, STsdb *pTsdb, SArray **ppLastArray, SC
 
         *pCol = (SLastCol){.ts = rowTs, .colVal = *pColVal};
         if (IS_VAR_DATA_TYPE(pColVal->type) /*&& pColVal->value.nData > 0*/) {
-          pCol->colVal.value.pData = taosMemoryMalloc(pCol->colVal.value.nData);
-          if (pCol->colVal.value.pData == NULL) {
-            terrno = TSDB_CODE_OUT_OF_MEMORY;
-            code = TSDB_CODE_OUT_OF_MEMORY;
-            goto _err;
-          }
           if (pColVal->value.nData > 0) {
+            pCol->colVal.value.pData = taosMemoryMalloc(pCol->colVal.value.nData);
+            if (pCol->colVal.value.pData == NULL) {
+              terrno = TSDB_CODE_OUT_OF_MEMORY;
+              code = TSDB_CODE_OUT_OF_MEMORY;
+              goto _err;
+            }
             memcpy(pCol->colVal.value.pData, pColVal->value.pData, pColVal->value.nData);
+          } else {
+            pCol->colVal.value.pData = NULL;
           }
         }
 
@@ -2795,17 +2799,21 @@ static int32_t mergeLastCid(tb_uid_t uid, STsdb *pTsdb, SArray **ppLastArray, SC
       tsdbRowGetColVal(pRow, pTSchema, slotIds[iCol], pColVal);
       if (!COL_VAL_IS_VALUE(tColVal) && COL_VAL_IS_VALUE(pColVal)) {
         SLastCol lastCol = {.ts = rowTs, .colVal = *pColVal};
-        if (IS_VAR_DATA_TYPE(pColVal->type) && pColVal->value.nData > 0) {
+        if (IS_VAR_DATA_TYPE(pColVal->type) /* && pColVal->value.nData > 0 */) {
           SLastCol *pLastCol = (SLastCol *)taosArrayGet(pColArray, iCol);
           taosMemoryFree(pLastCol->colVal.value.pData);
 
-          lastCol.colVal.value.pData = taosMemoryMalloc(lastCol.colVal.value.nData);
-          if (lastCol.colVal.value.pData == NULL) {
-            terrno = TSDB_CODE_OUT_OF_MEMORY;
-            code = TSDB_CODE_OUT_OF_MEMORY;
-            goto _err;
+          if (pColVal->value.nData > 0) {
+            lastCol.colVal.value.pData = taosMemoryMalloc(lastCol.colVal.value.nData);
+            if (lastCol.colVal.value.pData == NULL) {
+              terrno = TSDB_CODE_OUT_OF_MEMORY;
+              code = TSDB_CODE_OUT_OF_MEMORY;
+              goto _err;
+            }
+            memcpy(lastCol.colVal.value.pData, pColVal->value.pData, pColVal->value.nData);
+          } else {
+            lastCol.colVal.value.pData = NULL;
           }
-          memcpy(lastCol.colVal.value.pData, pColVal->value.pData, pColVal->value.nData);
         }
 
         taosArraySet(pColArray, iCol, &lastCol);
@@ -2916,14 +2924,18 @@ static int32_t mergeLastRowCid(tb_uid_t uid, STsdb *pTsdb, SArray **ppLastArray,
 
       *pCol = (SLastCol){.ts = rowTs, .colVal = *pColVal};
       if (IS_VAR_DATA_TYPE(pColVal->type) /*&& pColVal->value.nData > 0*/) {
-        pCol->colVal.value.pData = taosMemoryMalloc(pCol->colVal.value.nData);
-        if (pCol->colVal.value.pData == NULL) {
-          terrno = TSDB_CODE_OUT_OF_MEMORY;
-          code = TSDB_CODE_OUT_OF_MEMORY;
-          goto _err;
-        }
         if (pColVal->value.nData > 0) {
-          memcpy(pCol->colVal.value.pData, pColVal->value.pData, pColVal->value.nData);
+          pCol->colVal.value.pData = taosMemoryMalloc(pCol->colVal.value.nData);
+          if (pCol->colVal.value.pData == NULL) {
+            terrno = TSDB_CODE_OUT_OF_MEMORY;
+            code = TSDB_CODE_OUT_OF_MEMORY;
+            goto _err;
+          }
+          if (pColVal->value.nData > 0) {
+            memcpy(pCol->colVal.value.pData, pColVal->value.pData, pColVal->value.nData);
+          }
+        } else {
+          pCol->colVal.value.pData = NULL;
         }
       }