如何删除表中的重复记录只保留其中一条？

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)

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

如果还查性别也相同大则如下:

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

2.group by方法

查数据:

　　select count(num), max(name) from student --列出重复的记录数，并列出他的name属性

　　group by num

　　having count(num) >1 --按num分组后找出表中num列重复，即出现次数大于一次

删数据：

　　delete from student

　　group by num

　　having count(num) >1

　　这样的话就把所有重复的都删除了。

3.用distinct方法 -对于小的表比较有用

create table table_new as select distinct * from table1 minux

truncate table table1;

insert into table1 select * from table_new;

delete select a.* from FLRK1 a inner join FLRK1 b on a.记录号=b.记录号 and

(a.[ID]=b.[ID] and a.入库日期=b.入库日期 and a.操作时间=b.操作时间)

delete from FLRK1 where 记录号 in

(select min(记录号) from FLRK1 group by 记录号 having count(记录号)>1)

A表结构：

ID RQ SJ C

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

1 2005-07-14 14:20:50 A1

2 2005-02-15 05:12:23 A1

3 2005-07-14 14:20:50 A1

4 2005-06-16 16:16:16 A2

5 2005-06-16 16:16:16 A2

6 2005-05-18 05:10:35 A3

7 2005-02-15 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 2005-07-14 14:20:50 A1

2 2005-02-15 05:12:23 A1

4 2005-06-16 16:16:16 A2

6 2005-05-18 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)

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

　　方法二

　　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）