求SQL语句

[xiaoyuppou]

请问怎样删除一个表中重复的行(即重复出现只保存最新的一次)?谢谢!

[dawugui]

--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
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








------------------------------------------------------------------------------------
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
------------------------------------------------------------------------------------------------
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）
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1)

[liangCK]

select distinct * into # from tb
truncate table tb
insert into tb select * from #
drop table #

[-狙击手-]

select *  into #
from tablename a
where not exists(select 1 from tablename where id = a.id and date > a.date)

truncate table tablename

insert tablename select * from #


drop  table #

[wzy_love_sly]

declare @tb table (id int,type int,date datetime)
insert into @tb select 1,1,'2008-01-14'
insert into @tb select 2,1,'2008-01-15'
insert into @tb select 3,1,'2008-01-16'
insert into @tb select 4,2,'2008-01-14'
insert into @tb select 5,2,'2008-01-15'
insert into @tb select 6,2,'2008-01-16'

delete @tb from @tb a 
where exists(select 1 from @tb where type=a.type and date>a.date) 

select * from @tb

id type date
3 1 2008-01-16 00:00:00.000
6 2 2008-01-16 00:00:00.000

[-狙击手-]

喔耶

[zyz0304360]

学习

[zyz0304360]

declare @tb table (id int,type int,date datetime)
insert into @tb select 1,1,'2008-01-14'
union all  select 2,1,'2008-01-15'
union all  select 3,1,'2008-01-16'
union all  select 4,2,'2008-01-14'
union all  select 5,2,'2008-01-15'
union all  select 6,2,'2008-01-16'

select * 
into #t
from @tb a 
where not exists(select * from @tb where type=a.type and date>a.date) 

select * from #t

[凌雯]

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) 

[JL99000]

怎么说呢
看你的操作是在什么时候进行的
比如每次插入数据时为了避免重复，那么可以用触发器

如果重复数据已经存在表中了，那么可以将想前几楼那么做