select qd.difficult_level,sum(case when qpd.result='right' then 1 else 0 end)/count(qpd.result) as correct_rate from user_profile as up inner join question_practice_detail as qpd on qpd.device_id=up.device_id inner join question_detail as qd on qd.question_id=qpd.question_id where up.university ='浙江大学' GROUP BY qd.difficult_level ORDER BY correct_rate ASC