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
    from exam_record
    where submit_time is not null
    group by uid
    having(count(submit_time)/count(DISTINCT substr(submit_time,1,7))>=3)
)
select
    i.tag
    ,count(r.exam_id) as tag_cnt
from examination_info i join exam_record r using(exam_id)
where r.uid in (select * from t1)
group by i.tag
order by tag_cnt desc