刪除重複數據的一種高效的方法

表demo是重複拷貝自dba_objects，有88萬左右，不重複的是27323，沒有索引

方法一：delete from demo a where a.rowid <> (select max(rowid) from demo b where
b.object_id=a.object_id);
耗時：幾個小時以上

方法二： delete from demo where rowid in
(select rid from
(select rowid rid,row_number() over(partition by object_id order by rowid) rn
from demo)
where rn <> 1 );
耗時：30秒

方法三： create table demo2 as
select object_id,owner... from
(select demo.*,row_number() over(partition by object_id order by rowid) rn from demo)
where rn = 1;
truncate table demo; insert into demo select * from demo2; drop table demo2;
共耗時： 10秒，適合大數據量的情況，產生更少回滾量；