题解 | #月均完成试卷数不小于3的用户爱作答的类别#

select tag,count(uid) as tag_cnt
from exam_record a
left join examination_info b on a.exam_id=b.exam_id 
where uid in (
select distinct uid
from exam_record
group by uid,date_format(start_time,'%Y%m')
having count(submit_time)>=3
) 
group by tag 
order by tag_cnt desc;

先得出当月完成次数>=3的用户uid，然后在连接的两个表中筛选出这些uid的记录，使用tag进行分组，求得相应数据