题解 | #浙大不同难度题目的正确率#
浙大不同难度题目的正确率
http://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c
sql入门级，还请大佬们看看我的这个性能怎么样
select qd.difficult_level,sum(if(qpd.result='right',1,0))/count(qpd.result) as rate from user_profile up,question_practice_detail qpd,question_detail qd where up.university='浙江大学' and up.device_id=qpd.device_id and qpd.question_id =qd.question_id group by qd.difficult_level order by rate