[mysql] select语句中比较两个max函数查询出来的时间，然后出现诡异的情况

$user_list=$user->alias(u)->field("u.user_id, u.user_money,(case when u.user_name<>'' then u.user_name else u.nick end) AS hym,u.user_name AS phone,u.rank_points AS rank_points,u.reg_time AS reg_time,u.nick AS nick,sa.shop_name AS shop_name,sum(goods_amount)+sum('total_amount') AS amounts,count(oi.order_id)+count(so.id) AS pay_count,$user_list=$user->alias(u)->field("u.user_id