diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index 111da6d6ba563b6b9b3166de7940f919b1581326..cfc8ae1a40f07cd4910aa3cfd1de2a0ba697b3e7 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -1995,6 +1995,22 @@ static FORCE_INLINE TSKEY getRowPTs(SColumnInfoData* pTsColInfo, int32_t rowInde
   return *(TSKEY*)colDataGetData(pTsColInfo, rowIndex);
 }
 
+static void prepareBuf(SqlFunctionCtx* pCtx) {
+  if (pCtx->subsidiaries.rowLen == 0) {
+    int32_t rowLen = 0;
+    for (int32_t j = 0; j < pCtx->subsidiaries.num; ++j) {
+      SqlFunctionCtx* pc = pCtx->subsidiaries.pCtx[j];
+      rowLen += pc->pExpr->base.resSchema.bytes;
+    }
+
+    pCtx->subsidiaries.rowLen = rowLen + pCtx->subsidiaries.num * sizeof(bool);
+    pCtx->subsidiaries.buf = taosMemoryMalloc(pCtx->subsidiaries.rowLen);
+  }
+
+  ASSERT(pCtx->subsidiaries.buf != NULL);
+  ASSERT(pCtx->subsidiaries.rowLen > 0);
+}
+
 static void firstlastSaveTupleData(const SSDataBlock* pSrcBlock, int32_t rowIndex, SqlFunctionCtx* pCtx,
                                    SFirstLastRes* pInfo) {
   if (pCtx->subsidiaries.num <= 0) {
@@ -2003,8 +2019,6 @@ static void firstlastSaveTupleData(const SSDataBlock* pSrcBlock, int32_t rowInde
 
   if (!pInfo->hasResult) {
     pInfo->pos = saveTupleData(pCtx, rowIndex, pSrcBlock, NULL);
-    ASSERT(pCtx->subsidiaries.buf != NULL);
-    ASSERT(pCtx->subsidiaries.rowLen > 0);
   } else {
     updateTupleData(pCtx, rowIndex, pSrcBlock, &pInfo->pos);
   }
@@ -2960,16 +2974,7 @@ static STuplePos doSaveTupleData(SSerializeDataHandle* pHandle, const void* pBuf
 }
 
 STuplePos saveTupleData(SqlFunctionCtx* pCtx, int32_t rowIndex, const SSDataBlock* pSrcBlock, const STupleKey* pKey) {
-  if (pCtx->subsidiaries.rowLen == 0) {
-    int32_t rowLen = 0;
-    for (int32_t j = 0; j < pCtx->subsidiaries.num; ++j) {
-      SqlFunctionCtx* pc = pCtx->subsidiaries.pCtx[j];
-      rowLen += pc->pExpr->base.resSchema.bytes;
-    }
-
-    pCtx->subsidiaries.rowLen = rowLen + pCtx->subsidiaries.num * sizeof(bool);
-    pCtx->subsidiaries.buf = taosMemoryMalloc(pCtx->subsidiaries.rowLen);
-  }
+  prepareBuf(pCtx);
 
   char* buf = serializeTupleData(pSrcBlock, rowIndex, &pCtx->subsidiaries, pCtx->subsidiaries.buf);
   return doSaveTupleData(&pCtx->saveHandle, buf, pCtx->subsidiaries.rowLen, pKey);
@@ -2989,6 +2994,8 @@ static int32_t doUpdateTupleData(SSerializeDataHandle* pHandle, const void* pBuf
 }
 
 int32_t updateTupleData(SqlFunctionCtx* pCtx, int32_t rowIndex, const SSDataBlock* pSrcBlock, STuplePos* pPos) {
+  prepareBuf(pCtx);
+
   char* buf = serializeTupleData(pSrcBlock, rowIndex, &pCtx->subsidiaries, pCtx->subsidiaries.buf);
   doUpdateTupleData(&pCtx->saveHandle, buf, pCtx->subsidiaries.rowLen, pPos);
   return TSDB_CODE_SUCCESS;