Oracle消除重复记录的几种方式

消除重复数据是数据清洗的头等大事，下面介绍比较常用的几种去重方式。

Distinct

删除重复的员工信息

select distinct(empno) from emp

Rowid

利用rowid结合max和min函数快速去重

select e.* from emp e where e.rowid = (select max(e.rowid) from emp e 

利用rowid结合max和min函数快速删除重复数据

delete e.* from emp e where e.rowid < (select max(e.rowid) from emp e

Group by

select deptno from emp group by deptno;

Row_number()

row_number是通过标记排号方式去重，如果有2条或以上的重复数据，直接筛选删除即可。

1.查看重复数据

select d.id,d.outer_code from  dict_depts_source d order by outer_code

2.标识重复数据

select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from  dict_depts_source d

3.删除重复数据

delete from dict_depts_source where id in(
select id from(select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from  dict_depts_source d)t
where t.row_flag > 1)

4.检查删除效果

select d.id,d.outer_code,row_number() over(partition by outer_code order by outer_code) row_flag from  dict_depts_source d