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 as tid,
        count(distinct uid) uv,
        count(start_time) pv
    from
        exam_record
    group by
        exam_id
    order by
        uv desc,
        pv desc
))a

union all

select * from(
(
    select
        question_id as tid,
        count(distinct uid) uv,
        count(submit_time) pv
    from
        practice_record
    group by
        question_id
    order by
        uv desc,
        pv desc
))b