题解 | #浙大不同难度题目的正确率#

SELECT qd.difficult_level,
        SUM(
            CASE WHEN qpd.result = 'right'
                THEN 1
                ELSE 0
            END
        ) / COUNT(qpd.question_id) AS correct_rate
FROM user_profile AS up
    INNER JOIN question_practice_detail AS qpd
        ON up.device_id = qpd.device_id
    INNER JOIN question_detail AS qd
        ON qpd.question_id = qd.question_id
WHERE up.university = '浙江大学'
GROUP BY qd.difficult_level
ORDER BY correct_rate ASC;