题解 | #每个题目和每份试卷被作答的人数和次数#

with table1 as ( 
    select exam_id as tid,  uid  , 'exam' as tag   # 构造一个 标签 方便后面按照 试卷题目分别排序
    from exam_record 
    union all 
    select question_id as tid,  uid , 'prac' as tag
    from practice_record
)

select tid , count(distinct uid) as uv, count(uid) as pv
from table1
group by tid , tag
order by tag asc , uv desc , pv desc