diff --git a/source/common/src/tdatablock.c b/source/common/src/tdatablock.c
index 63e009ed0a..f30a74bf11 100644
--- a/source/common/src/tdatablock.c
+++ b/source/common/src/tdatablock.c
@@ -225,12 +225,16 @@ int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, co
     // Handle the bitmap
     char* p = taosMemoryRealloc(pColumnInfoData->varmeta.offset, sizeof(int32_t) * (numOfRow1 + numOfRow2));
     if (p == NULL) {
-      // TODO
+      return TSDB_CODE_OUT_OF_MEMORY;
     }
 
     pColumnInfoData->varmeta.offset = (int32_t*)p;
     for (int32_t i = 0; i < numOfRow2; ++i) {
-      pColumnInfoData->varmeta.offset[i + numOfRow1] = pSource->varmeta.offset[i] + pColumnInfoData->varmeta.length;
+      if (pSource->varmeta.offset[i] == -1) {
+        pColumnInfoData->varmeta.offset[i + numOfRow1] = -1;
+      } else {
+        pColumnInfoData->varmeta.offset[i + numOfRow1] = pSource->varmeta.offset[i] + pColumnInfoData->varmeta.length;
+      }
     }
 
     // copy data
@@ -239,7 +243,7 @@ int32_t colDataMergeCol(SColumnInfoData* pColumnInfoData, uint32_t numOfRow1, co
     if (pColumnInfoData->varmeta.allocLen < len + oldLen) {
       char* tmp = taosMemoryRealloc(pColumnInfoData->pData, len + oldLen);
       if (tmp == NULL) {
-        return TSDB_CODE_VND_OUT_OF_MEMORY;
+        return TSDB_CODE_OUT_OF_MEMORY;
       }
 
       pColumnInfoData->pData = tmp;
diff --git a/source/libs/executor/src/executorimpl.c b/source/libs/executor/src/executorimpl.c
index 1da0409fb8..51f11b20ac 100644
--- a/source/libs/executor/src/executorimpl.c
+++ b/source/libs/executor/src/executorimpl.c
@@ -5005,6 +5005,7 @@ static int32_t handleLimitOffset(SOperatorInfo* pOperator, SSDataBlock* pBlock)
     return PROJECT_RETRIEVE_DONE;
   }
 
+  // todo optimize performance
   // If there are slimit/soffset value exists, multi-round result can not be packed into one group, since the
   // they may not belong to the same group the limit/offset value is not valid in this case.
   if (pRes->info.rows >= pOperator->resultInfo.threshold || pProjectInfo->slimit.offset != -1 || pProjectInfo->slimit.limit != -1) {