diff --git a/src/client/src/tscAsync.c b/src/client/src/tscAsync.c
index e38020669631376cf111fbb543ec3c6deb400f41..6ab4eeaa8a3dd54eb61f14d75d97e34e64a2390d 100644
--- a/src/client/src/tscAsync.c
+++ b/src/client/src/tscAsync.c
@@ -54,7 +54,7 @@ void doAsyncQuery(STscObj* pObj, SSqlObj* pSql, void (*fp)(), void* param, const
     return;
   }
 
-  strtolower(pSql->sqlstr, sqlstr);
+  strntolower(pSql->sqlstr, sqlstr, sqlLen);
 
   tscDebugL("%p SQL: %s", pSql, pSql->sqlstr);
   pSql->cmd.curSql = pSql->sqlstr;
diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index 5d5e5469430721079753ff3d4badd0e40e77d1d2..0677463d8d01df899a377c7390a22743aa9b22ed 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -263,12 +263,29 @@ TAOS_RES* taos_query(TAOS *taos, const char *sqlstr) {
   return pSql;
 }
 TAOS_RES* taos_query_c(TAOS *taos, const char *sqlstr, uint32_t sqlLen) {
-  char* buf = malloc(sqlLen + 1);
-  buf[sqlLen] = 0;
-  strncpy(buf, sqlstr, sqlLen);
-  TAOS_RES *res = taos_query(taos, buf);
-  free(buf);
-  return res; 
+  STscObj *pObj = (STscObj *)taos;
+  if (pObj == NULL || pObj->signature != pObj) {
+    terrno = TSDB_CODE_TSC_DISCONNECTED;
+    return NULL;
+  }
+  
+  if (sqlLen > tsMaxSQLStringLen) {
+    tscError("sql string exceeds max length:%d", tsMaxSQLStringLen);
+    terrno = TSDB_CODE_TSC_INVALID_SQL;
+    return NULL;
+  }
+  
+  SSqlObj* pSql = calloc(1, sizeof(SSqlObj));
+  if (pSql == NULL) {
+    tscError("failed to malloc sqlObj");
+    terrno = TSDB_CODE_TSC_OUT_OF_MEMORY;
+    return NULL;
+  }
+  
+  doAsyncQuery(pObj, pSql, waitForQueryRsp, taos, sqlstr, sqlLen);
+
+  tsem_wait(&pSql->rspSem);
+  return pSql; 
 }
 int taos_result_precision(TAOS_RES *res) {
   SSqlObj *pSql = (SSqlObj *)res;
diff --git a/src/util/inc/tutil.h b/src/util/inc/tutil.h
index 1ba57bbaaa670cbd9aca7b19252a3bd745187130..f7c69e3973ad6fdefd4ef33f4a813221eedebe6d 100644
--- a/src/util/inc/tutil.h
+++ b/src/util/inc/tutil.h
@@ -133,6 +133,8 @@ char **strsplit(char *src, const char *delim, int32_t *num);
 
 char* strtolower(char *dst, const char *src);
 
+char* strntolower(char *dst, const char *src, int32_t n);
+
 int64_t strnatoi(char *num, int32_t len);
 
 //char* strreplace(const char* str, const char* pattern, const char* rep);
diff --git a/src/util/src/tutil.c b/src/util/src/tutil.c
index 1a74359f47af23d0073f41901f86282e3654e212..c8df34e1cd4e71954bf9255cc1507b5bb82d519b 100644
--- a/src/util/src/tutil.c
+++ b/src/util/src/tutil.c
@@ -234,6 +234,32 @@ char* strtolower(char *dst, const char *src) {
   *p = 0;
   return dst;
 }
+char* strntolower(char *dst, const char *src, int32_t n) {
+  int esc = 0;
+  char quote = 0, *p = dst, c;
+
+  assert(dst != NULL);
+
+  for (c = *src++; n-- > 0; c = *src++) {
+    if (esc) {
+      esc = 0;
+    } else if (quote) {
+      if (c == '\\') {
+        esc = 1;
+      } else if (c == quote) {
+        quote = 0;
+      }
+    } else if (c >= 'A' && c <= 'Z') {
+      c -= 'A' - 'a';
+    } else if (c == '\'' || c == '"') {
+      quote = c;
+    }
+    *p++ = c;
+  }
+
+  *p = 0;
+  return dst;
+}
 
 char *paGetToken(char *string, char **token, int32_t *tokenLen) {
   char quote = 0;