刪除重復數據的一種高效的方法
表demo是重復拷貝自dba_objects,有88萬左右,不重復的是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.*,