题解 | 浙大不同难度题目的正确率

SELECT
    qd.difficult_level,
    ROUND(SUM(if(qpd.result = 'right',1,0))/count(qpd.device_id),4) AS correct_rate
FROM
    user_profile up,
    question_practice_detail qpd,
    question_detail qd
WHERE 
    up.university= '浙江大学'
    AND up.device_id = qpd.device_id AND qpd.question_id = qd.question_id
GROUP BY qd.difficult_level
ORDER BY correct_rate ASC