php查询oracle date时间

$sql = "SELECT  M.order_no,to_char(M.order_date,'YYYY-MM-DD HH24:MI:SS') as order_time  FROM order_m M, order_d D WHERE   M .order_no = D .order_no AND M .confirm_mark = '*' AND D .retn_mark IS NULL  AND D .dlvd_qty - D .retn_qty - D .req_qty > 0 AND M .login_name = '".session('login_name')."' GROUP BY M.order_no,M.order_date ORDER BY M.order_date desc";

注：聚组函数以外的所有字段都要出现在group by后面.        不然会报错提示group by不是表达式