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

得加select *，只加括号不行