题解 | #浙大不同难度题目的正确率#

SELECT difficult_level,
AVG(IF(result='right',1,0)) AS correct_rate
FROM user_profile u, question_practice_detail qpd, question_detail qd
WHERE u.device_id = qpd.device_id AND qpd.question_id = qd.question_id
AND university='浙江大学'
GROUP BY difficult_level
ORDER BY correct_rate;