在oracle中，可以利用count()函数来查询重复字段，语法为“select * from 表名 where 字段 in(select 字段 from 表名 group by 字段 having count(字段) >1)”。
本教程操作环境：Windows10系统、Oracle 11g版、Dell G3电脑。
1、查找表中多余的重复记录，重复记录是根据单个字段（userCode）来判断
select * from user where userCode in (select userCode from user group by userCode having count (userCode) > 1)
2、删除表中多余的重复记录，重复记录是根据单个字段（userCode）来判断，只留有rowid最小的记录
delete from user where userCode in (select userCode from user group by userCode having count (peopleId) > 1) and rowid not in (select min(rowid) from user group by userCode having count(userCode)>1)
3、查找表中多余的重复记录（多个字段）
select * from user a where (a.userCode,a.userName) in (select userCode,userName from user group by userCode,userName 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 user a where (a.userCode,a.userName) in (select userCode,userName from user group by userCode,userName having count(*) > 1) and rowid not in (select min(rowid) from user group by userCode,userName 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 user a where (a.userCode,a.userName) in (select userCode,userName from user group by userCode,userName having count(*) > 1) and rowid not in (select min(rowid) from user group by userCode,userName having count(*)>1)
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