题解 | #月均完成试卷数不小于3的用户爱作答的类别#

with t1 as(
    select uid,tag,start_time,submit_time,score
    from exam_record e1
    left join examination_info e2 
    on e1.exam_id=e2.exam_id
)

select tag,count(*) tag_cnt
from t1
where uid in (select uid from t1
where submit_time is not null
group by uid,date_format(submit_time,'%Y%m')
having count(submit_time) >=3) 
group by tag
order by tag_cnt desc