Question

两个字段确定唯一一条记录但是现在出现很多重复记录如何删除多余的呢？？

Answer 1

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）
3、部分关键字段重复，且记录中有ID.
第一种方法可一次删除所有重复的..(只保留重复中ID最小的记录)。
delete from table where id not in ( select min(id) from table group by name)
第二种方法每次只删除重复中ID最大的一条记录。

delete from table where id in ( select max(id) from table group by name having count(*)>1)
4、SQL程序删除
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

自己还得出的办法：
select * from user1 where [id] not in (select top 1 [id] from user1 a where name=user1.name)
--删就这样写
delete from user1 where [id] not in (select top 1 [id] from user1 a where name=user1.name)
或 delete from user where id not in ( select max(id) from user where name=user.name)
delete [user] where id not in (select max(id) from [user] group by name having count(*) > 1)
max 或 min看具体情况而论。

其他方法：
----A:保留id最大的行,删除其它行
--方法1
delete [user] from [user] t
inner join(select name,max(id) as id from [user] group by name) a
on t.name = a.name and t.id <> a.id
--方法2
delete [user] from [user] t
where exists(select * from [user] where name = t.name and id > t.id)

----B:保留id最小的行,删除其它行
--方法1
delete [user] from [user] t
inner join(select name,min(id) as id from [user] group by name) a
on t.name = a.name and t.id <> a.id
--方法2
delete [user] from [user] t
where exists(select * from [user] where name = t.name and id < t.id)

----C:删除所有重复的name行,一行也不留
delete [user] from [user] t
inner join
(select id from [user] a where exists(select * from [user] where name = a.name group by name having count(*) > 1)) as b
on t.id = b.id