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关于MYSQL中每个用户取1条记录的三种写法(group by xxx)
来源: 互联网 发布时间:2014-10-10
本文导语: 今天以前的同学问我关于这方面的SQL语句,我特意记忆一下,毕竟这个也比较常见了 代码如下:select * from (select * from member_payment order by id desc) t group by member_id limit 10第一种是先排序,然后group,这样的话...
今天以前的同学问我关于这方面的SQL语句,我特意记忆一下,毕竟这个也比较常见了
select * from (select * from member_payment
order by id desc) t group by member_id limit 10
第一种是先排序,然后group,这样的话自然可以取到最适合的一条数据。
缺点很明显:Using temporary; Using filesort
select s.*
from (SELECT max(id) as id FROM `member_payment` group by `member_id` limit 10) t
left join `member_payment` as s on t.id=s.id
第二种是联合查询
select * from `member_payment` where EXISTS (
select `id` from (
SELECT max(`id`) as id FROM `member_payment` group by `member_id` limit 10) t
where t.`id`=`member_payment`.`id`
)
第三种是子查询
窃以为第二种效率最高
代码如下:
select * from (select * from member_payment
order by id desc) t group by member_id limit 10
第一种是先排序,然后group,这样的话自然可以取到最适合的一条数据。
缺点很明显:Using temporary; Using filesort
代码如下:
select s.*
from (SELECT max(id) as id FROM `member_payment` group by `member_id` limit 10) t
left join `member_payment` as s on t.id=s.id
第二种是联合查询
代码如下:
select * from `member_payment` where EXISTS (
select `id` from (
SELECT max(`id`) as id FROM `member_payment` group by `member_id` limit 10) t
where t.`id`=`member_payment`.`id`
)
第三种是子查询
窃以为第二种效率最高