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 as er left join examination_info as ei
using(exam_id)
where uid in
(SELECT
    uid
FROM
    exam_record
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