diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index f33e1e292e9a583fc8d9405041c83b5c9a166a3b..c46662097b734da70e67d5b7511991f529b17d67 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -32,6 +32,14 @@
 static void freeQueryInfoImpl(SQueryInfo* pQueryInfo);
 static void clearAllTableMetaInfo(SQueryInfo* pQueryInfo);
 
+static void tscStrToLower(char *str, int32_t n) {
+  if (str == NULL || n <= 0) { return;}
+  for (int32_t i = 0; i < n; i++) {
+    if (str[i] >= 'A' && str[i] <= 'Z') {
+        str[i] -= ('A' - 'a');
+    }
+  }
+}
 SCond* tsGetSTableQueryCond(STagCond* pTagCond, uint64_t uid) {
   if (pTagCond->pCond == NULL) {
     return NULL;
@@ -1422,7 +1430,7 @@ int32_t tscValidateName(SStrToken* pToken) {
     if (pToken->type == TK_STRING) {
        
       strdequote(pToken->z);
-      strntolower(pToken->z, pToken->z, pToken->n);
+      tscStrToLower(pToken->z, pToken->n);
       pToken->n = (uint32_t)strtrim(pToken->z);
        
       int len = tSQLGetToken(pToken->z, &pToken->type);
@@ -1477,8 +1485,6 @@ int32_t tscValidateName(SStrToken* pToken) {
       return TSDB_CODE_TSC_INVALID_SQL;
     }
     
-    strntolower(pToken->z, pToken->z, pToken->n);
-
     // re-build the whole name string
     if (pStr[firstPartLen] == TS_PATH_DELIMITER[0]) {
       // first part do not have quote do nothing
@@ -1491,7 +1497,7 @@ int32_t tscValidateName(SStrToken* pToken) {
     pToken->n += (firstPartLen + sizeof(TS_PATH_DELIMITER[0]));
     pToken->z = pStr;
 
-    strntolower(pToken->z, pToken->z, pToken->n);
+    tscStrToLower(pToken->z,pToken->n);
   }
 
   return TSDB_CODE_SUCCESS;