Oracle 删除重复数据只留一条

1、查找表中多余的重复记录，重复记录是根据单个字段（Id）来判断

 

select * from 表 where Id in (select Id from 表 group byId having count(Id) > 1)

 

2、删除表中多余的重复记录，重复记录是根据单个字段（Id）来判断，只留有rowid最小的记录

 

DELETE from 表 WHERE (id) IN ( SELECT id FROM 表 GROUP BY id HAVING COUNT(id) > 1) AND ROWID NOT IN (SELECT MIN(ROWID) FROM 表 GROUP BY id HAVING COUNT(*) > 1);

 

3、查找表中多余的重复记录（多个字段）

 

select * from 表 a where (a.Id,a.seq) in(select Id,seq from 表 group by Id,seq having count(*) > 1)

 

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录

 

delete from 表 a where (a.Id,a.seq) in (select Id,seq from 表 group by Id,seq having count(*) > 1) and rowid not in (select min(rowid) from 表 group by Id,seq having count(*)>1)

 

5、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

 

select * from 表 a where (a.Id,a.seq) in (select Id,seq from 表 group by Id,seq having count(*) > 1) and rowid not in (select min(rowid) from 表 group by Id,seq having count(*)>1)

  

上述转载自：http://www.cnblogs.com/252e/archive/2012/09/13/2682817.html

 

 

　　实际项目遇见千万级别的数据时，删除重复的数据并不适用(在oracle上800多万条数据用伤处方法去重复N个小时没有结果)。

　　下面给出在大数据情况下的去重复操作：

1. 建临时表：CREATE TABLE  tt as select a.name, MAX(a.ROWID) dataid from tablenamea GROUP BY a.name;  或 CREATE TABLE tt AS (select distinct * from tablename);
2. 清空原表数据：truncatetable tablename;
3. 将临时表数据填充到原表中：insert into tablename (select * from tt);　--千万级别数据2分钟左右完成
4. 删除临时表：drop table tt;
5. 提交：commit