题解 | #浙大不同难度题目的正确率#

SELECT 
    difficult_level,
    count(if(result = 'right', 1, null))/count(a.question_id)  correct_rate
FROM question_practice_detail a 
left join question_detail b 
on a.question_id = b.question_id
inner join 
(
    select 
        *
    from user_profile
    where university = '浙江大学'
) c 
on a.device_id = c.device_id
group by 
    1
order by 
    correct_rate;