在实际工作中,我们经常碰到这样的工作情况,取出用户订单中给定用户的最大单笔购买金额,此时,可以用到mysql的按字段分组取最大值,操作如下:
表(user_order)结构如下,我的操作是取出uid对应的最大的buy_time
方法0:
select uid,max(buy_time) from user_order group by uid
方法一:
select uid,buy_time from (select uid,buy_time from user_order order by buy_time desc) as a group by a.uid
方法二:
select a.* from
user_order as a where buy_time = (select max(buy_time) fromuser_order where a.uid=uid)
方法三:
select a.* from
user_order as a where not exists (select * from
user_order where uid=a.uid_id and buy_time>a.buy_time)
方法四:
select a.* from user_order as a where exists (select count(*) from user_order where uid=a.uid and buy_time>a.buy_time count(*)=0)