删除 类别相同 的最大值

delete from tab where id not in (

select id from tab t1 where n1=(

select min(n1) from tab t2 where s1=t1.s1

)

)

--------------------------------

delete tab where id not in(

select tab.id from tab,

(select min(n1) as n1,s1 from tab group by s1) B where tab.n1=B.n1 and tab.s1=B.s1)

 

连表的目的 是为了 得到 ID