关于数据重复的问题··大虾近来帮忙？

[新手学习着呢]

我的数据库中有近20000条记录，但是里面有1000条左右为重复数据，我现在想把里面的数据都修改为唯一值得，也就是说想把所有重复的数据删除掉，或者把所有单一的数据提取出来，不知如何操作？？ 请大虾之点一二!!!!!!!!!!!!!!!!!
我的标里面重复的字段名为：username 是用户名 具体我该怎么做，，大虾快帮以下
···

[txlicenhe]

delete 表 where username in
(select username from 表 group by username having sum(1) > 1)

[friendliu]

select distinct * into #tmp from tablename
go
delete from tablename
go
insert into tablename
select * from #tmp
go

[antoversky]

如果是foxpro,select distinct *into table tablename
from source_tablename
若是sql server:select distinct *into tablename
from source_tablename

[meteorlg]

delete from tablename where id in
(select max(id) from tablename group by username having count(*)>1)

[pengdali]

delete 你的表 where 编号 not in (select min(编号) from 你的表 group by username having sum(1)>1)

[pengdali]

如果你的表没有编号：

alter table 表 add 编号 int identity(1,1)

delete 你的表 where 编号 not in (select min(编号) from 你的表 group by username having sum(1)>1)

alter table 表 drop column 编