去重
第一種：distinct
create table tmp_t3 as select distinct * from t3;
drop table t3;
alter table tmp_t2 rename to t3;
-- 第二種，用rowid
delete from t2
where rowid <>( select min(rowid)
from t2 b
where b.c1 = t2.c1
and b.c2 = t2.c2 )
---第三種， 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)
---第四種， 用分析函數
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);