题解 | #月均完成试卷数不小于3的用户爱作答的类别#
月均完成试卷数不小于3的用户爱作答的类别
http://www.nowcoder.com/practice/b1d13efcfa0c4ecea517afbdb9090845
select tag,count() as tag_cnt from exam_record left 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()/count(distinct month(submit_time)) >=3) group by tag order by tag_cnt desc;