题解 | #统计复旦用户8月练题情况#
浙大不同难度题目的正确率
http://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c
select
t3.difficult_level,
sum(if(t2.result = 'right',1,0))/count(1) as correct_rate
from (select device_id from user_profile where university = '浙江大学')t1
join question_practice_detail t2
on t1.device_id = t2.device_id
join question_detail t3
on t2.question_id = t3.question_id
group by t3.difficult_level
order by correct_rate
