题解 | #月均完成试卷数不小于3的用户爱作答的类别#

select b.tag,count(*) tag_cnt
from exam_record a join examination_info b on a.exam_id=b.exam_id and a.uid in 
(select a.uid z
from exam_record a join examination_info b on a.exam_id=b.exam_id 
group by a.uid,LEFT(submit_time,7)
having count(a.submit_time)>=3) 
group by b.tag
order by tag_cnt desc