#思路:①先选出9月份完成试卷>=3的uid;②两表连接,将之前选出的uid作为子查询条件,再根据tag分组计数即可; select tag, count(tag) tag_cnt from exam_record left join examination_info using(exam_id) where uid in (select uid from exam_record where date_format(submit_time,'%Y%m')='202109' group by uid having count(score)>=3) group by tag order by tag_cnt desc