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MYSQL每个用户取1条记录的三种写法（group by xxx）
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
[sql]
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
[sql]
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
[sql]
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
