delete tablename where id not in( select max(id) from tablename group by email )
有两个意义上的重复记录,一是完全重复的记录,也即所有字段均重复的记录,二是部分关键字段重复的记录,比如Name字段重复,而其他字段不一定重复或都重复可以忽略。 1、对于第一种重复,比较容易解决,使用 select distinct * from tableName 就可以得到无重复记录的结果集。 如果该表需要删除重复的记录(重复记录保留1条),可以按以下方法删除 select distinct * into #Tmp from tableName drop table tableName select * into tableName from #Tmp drop table #Tmp 发生这种重复的原因是表设计不周产生的,增加唯一索引列即可解决。2、这类重复问题通常要求保留重复记录中的第一条记录,操作方法如下 假设有重复的字段为Name,Address,要求得到这两个字段唯一的结果集 select identity(int,1,1) as autoID, * into #Tmp from tableName select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID select * from #Tmp where autoID in(select autoID from #tmp2) 最后一个select即得到了Name,Address不重复的结果集(但多了一个autoID字段,实际写时可以写在select子句中省去此列)
select @ from tablename where email in (select distinct email from tablename)
如上,保留 1 [email protected] 這條select * from T inner join (select email,min(id) as id from T group by email) A on T.email=A.email and T.id=A.id
按楼主的意思,我觉得应该要删除了,不是不显示,那应该是: delete tablename where id not in( select max(id) from tablename group by email )
如果有唯一标识/主键(id)的使用方法 select * from 表A a where not exists(select 1 from 表A where email=a.email and id<a.id)--定义要保留的值 delete a 表A a where not exists(select 1 from 表A where email=a.email and id<a.id)
create table ta(id int identity(1,1),name varchar(50)) insert ta select 'b' /* id name ----------- -------------------------------------------------- 1 a 2 a 3 a 4 a 5 a 6 a 7 b 8 b 9 b 10 b 11 b 12 b(所影响的行数为 12 行) */select * from ta a where exists(select 1 from ta where name=a.name and id>a.id)--保留大的 select * from ta a where exists(select 1 from ta where name=a.name and id>a.id)--保留小的
delete t from tablename t where id not in(select min(id) from tabalename l group by l.email having count(*) > 1)and id not in(select min(id) from tabalename l group by l.email having count(*) = 1)
select max(id) from tablename group by email
)
1、对于第一种重复,比较容易解决,使用
select distinct * from tableName
就可以得到无重复记录的结果集。
如果该表需要删除重复的记录(重复记录保留1条),可以按以下方法删除
select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
发生这种重复的原因是表设计不周产生的,增加唯一索引列即可解决。2、这类重复问题通常要求保留重复记录中的第一条记录,操作方法如下
假设有重复的字段为Name,Address,要求得到这两个字段唯一的结果集
select identity(int,1,1) as autoID, * into #Tmp from tableName
select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
select * from #Tmp where autoID in(select autoID from #tmp2)
最后一个select即得到了Name,Address不重复的结果集(但多了一个autoID字段,实际写时可以写在select子句中省去此列)
筆如
id email
1 [email protected]
2 [email protected]
3 [email protected]保留哪條?
inner join
(select email,min(id) as id from T group by email) A
on T.email=A.email and T.id=A.id
delete tablename where id not in(
select max(id) from tablename group by email
)
select * from 表A a
where not exists(select 1 from 表A where email=a.email and id<a.id)--定义要保留的值
delete a
表A a
where not exists(select 1 from 表A where email=a.email and id<a.id)
insert ta
select 'b'
/*
id name
----------- --------------------------------------------------
1 a
2 a
3 a
4 a
5 a
6 a
7 b
8 b
9 b
10 b
11 b
12 b(所影响的行数为 12 行)
*/select * from ta a
where exists(select 1 from ta where name=a.name and id>a.id)--保留大的
select * from ta a
where exists(select 1 from ta where name=a.name and id>a.id)--保留小的
group by l.email
having count(*) > 1)and id not in(select min(id) from tabalename l
group by l.email
having count(*) = 1)
注意:
对所有的记录只针对email字段重复,如重复只保留第一条.其他字段重复与否不予考虑.
id email1 [email protected]
2 [email protected]
3 [email protected]
4 [email protected]
5 [email protected]
....
-------------
执行后应该数据库表中只有
id email
1 [email protected]
2 [email protected]
5 [email protected]
....
select min(id) from tablename group by email
)
select @i count(*) from table where condition
set recordcout = @i -1
delete from table where condition