在网络上，看到过这样的mysql语句，但是在效率极差。
如：
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.val select a.*
如：
select a.* from tb a where 2 > (select count(*) from tb where name = a.name and val < a.val ) order by a.name,a.val select a.*
