怎么样抽取重复记录

[A]select * from table t1 where where t1.rowed != 
(select max(rowed) from table t2 
where t1.id=t2.id and t1.name=t2.name) 
或者 
select count(*), t.col_a,t.col_b from table t 
group by col_a,col_b 
having count(*)>1