题解 | 浙大不同难度题目的正确率
SELECT difficult_level, SUM(result)/COUNT(question_id) correct_rate FROM (SELECT qpd.device_id, qpd.question_id, qd.difficult_level, IF(qpd.result = 'right',1,0) result FROM question_practice_detail qpd JOIN user_profile up ON qpd.device_id = up.device_id JOIN question_detail qd ON qpd.question_id = qd.question_id WHERE up.university = '浙江大学') table1 GROUP BY difficult_level ORDER BY correct_rate