mysql对表中数据根据某一字段去重

要删除重复的记录，就要先查出重复的记录，这个很容易做到

select * from 表名 group by 根据哪一个字段（简称字段） having count(字段) > 1

注意：这是查出所有重复记录的第一条记录，需要保留，因此需要添加查询条件，查出所有的重复记录

select id,expect from cqssc where expect in (select expect from cqssc group by expect having count(expect)>1) 

and id not in(select min(id) from cqssc group by expect having count(expect)>1)

然后

delete from cqssc where id in (select id from (select id from cqssc where expect in 

(select expect from cqssc group by expect having count(expect)>1) and id not in

(select min(id) from cqssc group by expect having count(expect)>1)) as tmpresult)

删除成功，最后再查询一下看是否还有重复记录