题解 | #浙大不同难度题目的正确率#

select c.difficult_level,
       sum(if(b.result='right',1,0)) / count(b.question_id) as correct_rate
from question_detail c
join question_practice_detail b using(question_id)
join user_profile a using(device_id)
where a.university = '浙江大学'
group by c.difficult_level
order by correct_rate

呜呜困难题我居然自己写出来了！！！