如何删除表中的重复记录?

类别:数据库 点击:0 评论:0 推荐:

--测试数据
/*-----------------------------
select * from tt
-----------------------------*/
id          pid        
----------- -----------
1           1
1           1
2           2
3           3
3           3
3           3

(所影响的行数为 6 行)

首先,如何查询table中有重复记录
select *,count(1) as rownum
from tt
group by id, pid
having count(1) > 1
id          pid         rownum     
----------- ----------- -----------
1           1           2
3           3           3

(所影响的行数为 2 行)

方法一:使用distinct和临时表
if object_id('tempdb..#tmp') is not null
drop table #tmp
select distinct * into #tmp from tt
truncate table tt
insert into tt select * from #tmp

方法二:添加标识列
alter table tt add NewID int identity(1,1)
go 
delete from tt  where exists(select 1 from tt a where  a.newid>tt.newid and tt.id=a.id and tt.pid=a.pid)
go
alter table tt drop column NewID
go

--测试结果
/*-----------------------------
select * from tt
-----------------------------*/
id          pid        
----------- -----------
1           1
2           2
3           3

(所影响的行数为 3 行)

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