删除数据库中重复的记录

时间:2022-10-23 22:15:53

如何按字段删除重复记录?

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

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

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