diff --git a/src/client/src/tscPrepare.c b/src/client/src/tscPrepare.c
index ea6ad8a48d7a9c4b5e992dffe8329735a0f47512..83a6a975631100356d378296ebacb8f801e86573 100644
--- a/src/client/src/tscPrepare.c
+++ b/src/client/src/tscPrepare.c
@@ -1658,7 +1658,7 @@ int taos_stmt_prepare(TAOS_STMT* stmt, const char* sql, unsigned long length) {
   pRes->qId = 0;
   pRes->numOfRows = 0;
 
-  strcpy(pSql->sqlstr, sql);
+  strntolower(pSql->sqlstr, sql, sqlLen);
   tscDebugL("0x%"PRIx64" SQL: %s", pSql->self, pSql->sqlstr);
 
   if (tscIsInsertData(pSql->sqlstr)) {
@@ -1850,6 +1850,18 @@ int taos_stmt_set_tbname_tags(TAOS_STMT* stmt, const char* name, TAOS_BIND* tags
     pCmd->insertParam.pTableBlockHashList = hashList;
   }
 
+  int32_t sqlLen = (int32_t)strlen(pStmt->pSql->sqlstr);
+  char* sqlstr = pStmt->pSql->sqlstr;
+  pStmt->pSql->sqlstr = calloc(1, sqlLen + 1);
+  if (pSql->sqlstr == NULL) {
+    tscError("0x%"PRIx64" failed to malloc sql string buffer", pSql->self);
+    free(tname.z);
+    STMT_RET(TSDB_CODE_TSC_OUT_OF_MEMORY);
+  }
+
+  strntolower(pStmt->pSql->sqlstr, sqlstr, sqlLen);
+  free(sqlstr);
+
   code = tsParseSql(pStmt->pSql, true);
   if (code == TSDB_CODE_TSC_ACTION_IN_PROGRESS) {
     // wait for the callback function to post the semaphore