删除表中重复数据，留下ID比较小的行
delete from 表 where [重复字段] in (select [重复字段] from 表 group by 字段 having count([字段]) > 1) and ID not in (select min(ID) from [表] group by [字段] having count([字段])> 1)
数据库删除数据表重复数据，只留下ID较小的行
原文：http://www.cnblogs.com/bluestream/p/4397806.html
