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