SQL-删除重复数据

例.

id name value

1 a pp

2 a pp

3 b iii

4 b pp

5 b pp

6 c pp

7 c pp

8 c iii

id是主键

1.要求得到如下结果：

id name value

2	a	pp
3	b	iii
5	b	pp
7	c	pp
8	c	iii

方法

delete YourTable

where [id] not in (

select max([id]) from YourTable

group by (name + value))

2.要求得到如下结果

id name value

1 a pp

3 b iii

4 b pp

6 c pp

8 c iii

方法

delete a

from 表 a left join(

select id=min(id) from 表 group by name,value

)b on a.id=b.id

where b.id is null

查询及删除重复记录的SQL语句

＂重复记录＂有两个意义上，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。

（一）第一种重复，可使用如下语句得到无重复记录的结果集：

select distinct * from tableName

　　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【待验证】。

（二）第二种重复：

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)

6、在A表中存在一个字段“name”，且不同记录之间的“name”值有可能会相同，

查询出在该表中的各记录之间，“name”值存在重复的项：

Select Name,Count(*) From A Group By Name Having Count(*) > 1

如果还查性别也相同，则如下：

Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1

(三) 【待验证】

方法一

declare @max integer,@id integer

declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1

open cur_rows

fetch cur_rows into @id,@max

while @@fetch_status=0

begin

select @max = @max -1

set rowcount @max

delete from 表名 where 主字段 = @id

fetch cur_rows into @id,@max

end

close cur_rows

set rowcount 0