ORACLE刪除重複資料的一種高效的方法
阿新 • • 發佈:2019-01-29
刪除重複資料的一種高效的方法
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;
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,適合大資料量的情況,產生更少回滾量;
來源:http://blog.csdn.net/xjzdr/article/details/2047530