select qd.difficult_level,count(if ((qpd.result='right'),1,null))/count(qpd.result) correct_rate from question_detail qd left join question_practice_detail qpd on qd.question_id=qpd.question_id left join user_profile up on qpd.device_id=up.device_id where up.university='浙江大学' group by qd.difficult_l...