题解 | #每个题目和每份试卷被作答的人数和次数#

(select exam_id as tid,count(distinct(uid)) as uv, count(exam_id) as pv from exam_record  group by tid )
union
(select question_id as tid,count(distinct(uid)) as uv,count(question_id) as pv from practice_record group by tid )
order by left(tid,1) desc,uv desc,pv desc