题解 | #每个题目和每份试卷被作答的人数和次数#

select * 
from (
    select exam_id tid, count(distinct uid) uv,
        count(*) pv
    from exam_record 
    group by exam_id
    order by uv desc, pv desc
) t1
union 
select *
from
(
    select question_id tid, count(distinct uid) uv,
        count(*) pv
    from practice_record 
    group by question_id
    order by uv desc, pv desc
) t2