select qd.difficult_level, sum(if(qpd.result='right',1,0)) / count(qpd.result) as correct_rate from question_practice_detail as qpd left join question_detail as qd on qd.question_id = qpd.question_id LEFT JOIN user_profile as up on up.device_id = qpd.device_id where up.university = '浙江大学' GROUP by q...