删除表中重复记录，只保留一条：

delete from 表名 where 字段ID in (select * from (select max(字段ID) from 表名 group by 重复的字段 having count(重复的字段) > 1) as b);

实例： 
2.当想要为某一个表建立一个唯一索引，由于表中有重复记录而无法进行时，需要删除重复记录。 
例表 dept

id_no            id_name

       100              'AAA'

       101              'BBB'

       102              'CCC'

       103              'DDD'

       100              'EEE'

       100              'FFF'

       103              'GGG'

请写一条(或一组)SQL语句，删除重复的行，但重复的行中需要保留一行， 
如上表，id_no=100需要删除2行，保留一行，id_no=101需要删除一行保留一行id_no=102和103则不删

delete from dept where id_no not in ( select * from (select max(id_no) from dept group by id_no having count(id_no)>1) b);

以上转自http://flyer0126.iteye.com/blog/497359

但是我的需求不太一样， 
| id | createTime | labId | pubId | 
+—–+———————+——-+————————————–+ 
| 171 | 2014-05-22 21:49:11 | 1 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 172 | 2014-05-22 21:49:11 | 2 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 173 | 2014-05-22 21:49:11 | 6 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 174 | 2014-05-22 21:49:11 | 5 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 175 | 2014-05-22 21:49:11 | 2 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 176 | 2014-05-22 21:49:11 | 6 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 177 | 2014-05-22 21:49:11 | 5 | d4165953-2245-4b8c-b21d-8c08d519f66e | 
| 178 | 2014-07-03 15:20:07 | 2 | d5308254-3b52-4ada-8e10-16b6a764c5e5 | 
| 179 | 2014-07-03 15:36:00 | 2 | d4bc80b4-b57b-4049-9ab3-8f45102fae91 | 
| 180 | 2014-07-04 21:05:26 | 4 | f8ccee8f-d93c-41cc-8d2f-28ada7ea4b07 | 
我需要把labId和pubId相同的重复记录删掉，只要labId和pubId有一项不同就不算重复记录。 
delete from t_publishandlabel where id not in ( select * from(select id from t_publishandlabel group by pubId,labId)b);