mysql->sql 一句sql 删除重复数据

面试常考的一道题：一句sql删除表里的重复数据。
偶尔和同事聊到这个问题就顺便写了下代码，供大家参考~


//数据准备

drop table t_user; 
create table t_user( 
id        int(5) not null auto_increment, 
username varchar(10), 
age       int(3), 
primary key(id) 
); 

insert into t_user(username,age) values('aaa',20); 
insert into t_user(username,age) values('aaa',20); 
insert into t_user(username,age) values('aaa',20); 
insert into t_user(username,age) values('bbb',20); 
insert into t_user(username,age) values('bbb',20); 
insert into t_user(username,age) values('ccc',20); 
insert into t_user(username,age) values('ccc',20); 
insert into t_user(username,age) values('ddd',20); 
insert into t_user(username,age) values('ddd',20); 

删除语句：

DELETE t
FROM
	t_user t,
	(
		SELECT
			min(id)AS ttid,
      username
		FROM
			t_user t2
		GROUP BY
			t2.username
	)AS tt
WHERE t.id > tt.ttid
 and t.username = tt.username;