4.16 删除重复记录

从表中删除重复记录，考虑如下所示的表：
create table dupes (id integer,name varchar(10));
insert into dupes values (1,‘NOPOLEON‘);
insert into dupes values (2,‘DYNAMITE‘);
insert into dupes values (3,‘DYNAMITE‘);
insert into dupes values (4,‘SHE SELLS‘);
insert into dupes values (5,‘SEA SHELLS‘);
insert into dupes values (6,‘SEA SHELLS‘);
insert into dupes values (7,‘SEA SHELLS‘);

select * from dupes order by 1;
+------+------------+
| id   | name       |
+------+------------+
|    1 | NOPOLEON   |
|    2 | DYNAMITE   |
|    3 | DYNAMITE   |
|    4 | SHE SELLS  |
|    5 | SEA SHELLS |
|    6 | SEA SHELLS |
|    7 | SEA SHELLS |
+------+------------+

解决方案：

delete from dupes 
 where id not in 
 (select minid from 
  (select min(id) as minid from dupes group by name) 
 b);