diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index c6ab9f859d..04d7396d12 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -2392,6 +2392,7 @@ int32_t firstFunction(SqlFunctionCtx* pCtx) {
   SInputColumnInfoData* pInput = &pCtx->input;
   SColumnInfoData*      pInputCol = pInput->pData[0];
 
+  int32_t type  = pInputCol->info.type;
   int32_t bytes = pInputCol->info.bytes;
   pInfo->bytes  = bytes;
 
@@ -2428,6 +2429,10 @@ int32_t firstFunction(SqlFunctionCtx* pCtx) {
       TSKEY cts = getRowPTs(pInput->pPTS, i);
 
       if (pResInfo->numOfRes == 0 || *(TSKEY*)(pInfo->buf + bytes) > cts) {
+        if (IS_VAR_DATA_TYPE(type)) {
+          bytes = varDataTLen(data);
+          pInfo->bytes = bytes;
+        }
         memcpy(pInfo->buf, data, bytes);
         *(TSKEY*)(pInfo->buf + bytes) = cts;
         pInfo->hasResult = true;
@@ -2458,6 +2463,10 @@ int32_t firstFunction(SqlFunctionCtx* pCtx) {
       TSKEY cts = getRowPTs(pInput->pPTS, i);
 
       if (pResInfo->numOfRes == 0 || *(TSKEY*)(pInfo->buf + bytes) > cts) {
+        if (IS_VAR_DATA_TYPE(type)) {
+          bytes = varDataTLen(data);
+          pInfo->bytes = bytes;
+        }
         memcpy(pInfo->buf, data, bytes);
         *(TSKEY*)(pInfo->buf + bytes) = cts;
         pInfo->hasResult = true;
@@ -2481,6 +2490,7 @@ int32_t lastFunction(SqlFunctionCtx* pCtx) {
   SInputColumnInfoData* pInput = &pCtx->input;
   SColumnInfoData*      pInputCol = pInput->pData[0];
 
+  int32_t type  = pInputCol->info.type;
   int32_t bytes = pInputCol->info.bytes;
   pInfo->bytes  = bytes;
 
@@ -2508,6 +2518,10 @@ int32_t lastFunction(SqlFunctionCtx* pCtx) {
       char* data = colDataGetData(pInputCol, i);
       TSKEY cts = getRowPTs(pInput->pPTS, i);
       if (pResInfo->numOfRes == 0 || *(TSKEY*)(pInfo->buf + bytes) < cts) {
+        if (IS_VAR_DATA_TYPE(type)) {
+          bytes = varDataTLen(data);
+          pInfo->bytes = bytes;
+        }
         memcpy(pInfo->buf, data, bytes);
         *(TSKEY*)(pInfo->buf + bytes) = cts;
         //        DO_UPDATE_TAG_COLUMNS(pCtx, ts);
@@ -2527,6 +2541,10 @@ int32_t lastFunction(SqlFunctionCtx* pCtx) {
       char* data = colDataGetData(pInputCol, i);
       TSKEY cts = getRowPTs(pInput->pPTS, i);
       if (pResInfo->numOfRes == 0 || *(TSKEY*)(pInfo->buf + bytes) < cts) {
+        if (IS_VAR_DATA_TYPE(type)) {
+          bytes = varDataTLen(data);
+          pInfo->bytes = bytes;
+        }
         memcpy(pInfo->buf, data, bytes);
         *(TSKEY*)(pInfo->buf + bytes) = cts;
         pInfo->hasResult = true;