#计算正确率 select d.difficult_level ,sum(if(q.result='right',1,0))/count(q.device_id) correct_rate from question_practice_detail q ,question_detail d,user_profile u where q.question_id=d.question_id and u.device_id=q.device_id and u.university='浙江大学' group by d.difficult_level order by correct_rate as...