删除数据库中的数据，为什么不成功，求指教！

            String connString = "Data Source =STRING\\STRING;Initial Catalog = Employee; Integrated Security =SSPI";
            SqlConnection conn = new SqlConnection(connString);
                conn.Open();
             String dss = string.Format("SELECT * FROM zhanghao");
             SqlDataAdapter da = new SqlDataAdapter(dss,conn);
             DataSet ds = new DataSet();
                da.Fill(ds, "zhanghao");
                string del = string.Format("DELETE FROM zhanghao where id=123");
             SqlCommand cmd = new SqlCommand(del);
                 da.DeleteCommand = cmd;
                 da.Update(ds, "zhanghao");
                 ds.Tables["zhanghao"].AcceptChanges();               
                 conn.Close();