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(start_time) AS tag_cnt
FROM exam_record
JOIN examination_info USING(exam_id) 
WHERE uid IN (SELECT uid
FROM
(SELECT
    uid,
    DATE_FORMAT(submit_time,'%Y%m') AS month,
    COUNT(submit_time) AS cnt
FROM exam_record
JOIN examination_info USING(exam_id)
GROUP BY uid,DATE_FORMAT(submit_time,'%Y%m')
HAVING cnt >= 3
)t1)
GROUP BY tag
ORDER BY tag_cnt DESC
LIMIT 3;