数据库重复记录是我们经常会面临的一个问题，青岛星网跟大家分享：ORACLE数据库查询删除重复记录的三种方法，可以使用1.用rowid方法2.用group by方法3.用distinct方法。
1.用rowid方法
2.用group by方法
3.用distinct方法
1、用rowid方法
据据oracle带的rowid属性，进行判断，是否存在重复,查数据:
select * from table1 a where rowid !=(select max(rowid) from table1 b where a.name1=b.name1 and a.name2=b.name2......)
删除数据代码
delete from table1 a where rowid !=(select max(rowid) from table1 b where a.name1=b.name1 and a.name2=b.name2......)
2、group by方法
查询数据代码
select count(num), max(name) from student --列出重复的记录数，并列出他的name属性 group by num having count(num) >1 --按num分组后找出表中num列重复，即出现次数大于一次
删除数据代码
delete from student group by num having count(num) >1
这样的话就把所有重复的都删除了。
3.用distinct方法
1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录
delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
3、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 vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
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