删除表中非主键字段重复的数据？
BLE中有一个字段CODE(不是主键字段)，CODE字段里面可能有很多组重复的数据，现在我想把那些重复的数据就留一条，其他的删除，要的那条数据随便哪条都可以，只要留下重复中的其中一条就可以了，请问怎么删除？

------解决方案--------------------
在几千条记录里,存在着些相同的记录,如何能用SQL语句,删除掉重复的呢?谢谢!
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、查找表中多余的重复记录（多个字段）
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq 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 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)

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 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)

------解决方案--------------------
请参阅下例

一张表里面以两个字段为唯一字段，当几条记录的这两个字段完全相同时，需要删除重复项，如下表
a b c d
1 2 3 4
1 5 3 5
1 2 7 9
以a、b为唯一字段，第一条和第三条的a、b完全相同，所以，需要删除第一条记录1 2 3 4 或者第三条记录1 2 7 9
即如下结果：
a b c d
1 2 3 4
1 5 3 5
或
a b c d
1 5 3 5
1 2 7 9

请问各位大侠这种sql语句怎么写


CREATE TABLE Tb1(id int, [a] varchar(255), [b] varchar(255), [c] varchar(255), [d] varchar(255))
INSERT Tb1(id, [a], [b], [c], [d])
SELECT 1, '1 ', '2 ', '3 ', '4 '
UNION ALL SELECT 2, '1 ', '5 ', '3 ', '5 '
UNION ALL SELECT 3, '1 ', '2 ', '7 ', '9 '
UNION ALL SELECT 4, '1 ', '4 ', '7 ', '6 '

delete Tb1 where [id] not in (select max([id]) from Tb1 group by a,b )
select * from tb1

drop table tb1

如果要同时删除第一和第三行
即如下结果：
a b c d
1 5 3 5

语句如下：

delete m from tb t
inner join
(
select a ,b
from tb
group by a , b
having count(*)> 1
)n
on m.a = n.a and m.b = n.b
或
delete * from tb as m,
(
select a ,b
from tb
group by a , b
having count(*)> 1
)n
where m.a = n.a and m.b = n.b
------解决方案--------------------
create table t
(

code int
)

insert into t
select 2 union all
select 2 union all
select 2

alter table t
add id int identity(1,1)

delete t
where id not in
(
select id from t a
where not exists(select 1 from t where a.code=code and id <a.id)
)

select * from t
code id
----------- -----------
2 1

（所影响的行数为 1 行）
------解决方案--------------------
or

delete ble
where name not in(select min(name) from ble group by code)

or

delete ble
where name not in(select max(name) from ble group by code)