题解 | #浙大不同难度题目的正确率#

select
    difficult_level,
    sum(if (qpd.result = 'right', 1, 0)) / count(up.device_id) as accuracy
from
    user_profile as up
    inner join question_practice_detail as qpd on up.device_id = qpd.device_id
    inner join question_detail qd on qpd.question_id = qd.question_id
where
    up.university = '浙江大学'
group by
    difficult_level
order by
    accuracy

• join方式选择：如果前面inner join改成left join，为了防止结果中有难度为None的结果，需要在order by前加一句 having qd.difficult_level != 'None'