Oracle 删除重复数据的几种方法

去重

第一种：distinct

create table tmp_t3 as select distinct * from t3;

drop table t3;

alter table tmp_t2 rename to t3;

-- 第二种，用rowid

delete from t2

    where rowid <>( select min(rowid)

                     from t2 b

                     where b.c1 = t2.c1

                       and b.c2 = t2.c2 )

 

---第三种， 用rowid + group by 的方法

delete from T2

    where rowid not in (select min(rowid)

    from t2 group by c1,c2 );

 

delete from t2 

where not exists (select 1 from (select min(rowid) rid from t2 group by c1,c2) b where b.rid=t2.rowid)

 

---第四种， 用分析函数

delete from t2 where rowid in 

(select b.rd from 

(select rowid rd,row_number() over(partition by c1,c2 order by c1) rn 

from t2) b 

where b.rn > 1);