题解 | #浙大不同难度题目的正确率#

select difficult_level,sum(if(result='right',1,0))/count(p.question_id) correct_rate
from
(select *
from
user_profile u 
where university="浙江大学") as t
inner join
question_practice_detail p
on t.device_id=p.device_id 
inner join
question_detail q 
on
q.question_id=p.question_id
group by difficult_level
order by correct_rate