题解 | #浙大不同难度题目的正确率#

SELECT
    qd.difficult_level,
    SUM(IF (result = 'right', 1, 0)) / COUNT(qpd.device_id) AS correct_rate
FROM
    question_detail AS qd
    LEFT JOIN question_practice_detail AS qpd ON qpd.question_id = qd.question_id
    LEFT JOIN user_profile AS up ON up.device_id = qpd.device_id
WHERE
    up.university = '浙江大学'
GrOUP BY
    qd.difficult_level
ORDER BY
    correct_rate ASC;