题解 | #每个题目和每份试卷被作答的人数和次数#

这道题的关键在于`order by` 是否起作用

select * from (
    select exam_id as tid, count(DISTINCT uid) as uv, count(uid) as pv
    from exam_record
    group by exam_id
    order by uv desc, pv desc
) as ta

union all

select * from (
    select question_id as tid, count(DISTINCT uid) as uv, count(uid) as pv
    from practice_record
    group by question_id
    order by uv desc, pv desc
) as tb