查询student表中手机号重复数据
select id,uid,mobile,count(*) as count from student group by mobile having count>1;
查询student表中id最小的重复数据
select max(id) from student group by uid having count(uid) > 1
删除student表中重复的id最小的数据
delete from student where id in (select minid from (select min(id) as minid from student group by mobile having count(mobile) > 1) as b);