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(1) as tag_cnt
from
    exam_record a
    left join examination_info b on a.exam_id = b.exam_id
where
    a.uid in (
        select
            uid
        from
            exam_record
        where
            score is not null
        group by
            year (start_time),
            month (start_time),
            uid
        having
            count(1) >= 3
    )
group by
    tag
order by
    count(1) desc