删除表中重复记录 只留一条即可

今天碰到一个在上万条记录里,存在着些相同的记录,只是主键和某个列不同，如何能用SQL语句,删除掉重复的呢?问题解答了很高兴，总结下。

1、如果记录所有字段的值都一样的，就是完全重复的话，我也觉得用SELECT   DISTINCT   *   FROM   生成一个临时表，删掉旧表的做法比较好。   

但表的记录并非完全重复，比如有个主id是唯一的，要求也是把另一个字段name相同的去掉，只保留一个。   

    delete     from   table   as   a   where   a.id     not   in(select   top   1   id   from   table   as   b   where   a.name   =b.name)  

2、

　　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。

　　a、对于第一种重复，比较容易解决，使用

1）、a）、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)

b)、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)

c)、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)

d)、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)

e)、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)

比方说在A表中存在一个字段“name”，而且不同记录之间的“name”值有可能会相同，

现在就是需要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

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。

　　b、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)

3、实例：

A表结构：

ID RQ SJ C

--------------------------------------------

1 2010-07-14 14:20:50 A1

2 2010-02-15 05:12:23 A1

3 2010-07-14 14:20:50 A1

4 2010-06-16 16:16:16 A2

5 2010-06-16 16:16:16 A2

6 2010-05-18 05:10:35 A3

7 2010-02-15 05:12:23 A1

--------------------------------------------

求SQL语句一条，把表A中　RQ,SJ,C　三个字段有相同的重复记录删除．

得到的结果：

ID RQ SJ C

--------------------------------------------

1 2010-07-14 14:20:50 A1

2 2010-02-15 05:12:23 A1

4 2010-06-16 16:16:16 A2

6 2010-05-18 05:10:35 A3

--------------------------------------------

Delete from A Where ID Not In (Select Min(ID) from A Group By RQ,SJ,C )

Delete a from tb a inner join tb as b on a.fid <b.fid and a.c=b.c and a.rq=b.rq and a.sj=b.sj

delete from A t

where exists(select 1 from A where ID <A.ID and SJ=t.SJ and RQ=t.RQ and C=t.c)