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(tag) as tag_cnt
from exam_record
join examination_info using(exam_id)
where uid in (
    select uid
    from exam_record
    where submit_time is not null
    group by uid
    having count(exam_id) / count(distinct DATE_FORMAT(start_time, "%Y%m")) >= 3
)
group by tag
order by tag_cnt desc

本题讲的是月均完成数不小于3，也就是说每个月完成3个考试，且考试类型可以重复