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(b.tag) tag_cnt
from
    exam_record a,
    examination_info b
where
    a.exam_id = b.exam_id
    and a.uid in (
	select
		uid
	from
		exam_record
	where
		submit_time is not null
	group by
		uid,
		date_format (submit_time,
		'%Y%m')
	having
		count(uid) >= 3)

group by
    b.tag
order by
    count(b.tag) desc