题解 | #每个题目和每份试卷被作答的人数和次数#

select 
    t1.exam_id             as tid ,
    count(distinct t1.uid) as uv  ,
    count(t1.uid)          as pv
from exam_record t1
group by t1.exam_id
union all
select 
    t2.question_id          as tid ,
    count(distinct t2.uid)  as uv  ,
    count(t2.uid)           as pv
from practice_record t2
group by t2.question_id 
order by substr(tid, 1, 1) desc, uv desc, pv desc # 如结果所示，tid也要降序显示（易漏点）
/*SQL*/;