题解 | #浙大不同难度题目的正确率#

SELECT
    difficult_level,
    SUM(IF(result='right',1,0)) / COUNT(*) correct_rate
FROM(
    SELECT
        up.device_id,
        qpd.question_id,
        qpd.result,
        qd.difficult_level
    FROM
        user_profile up
    JOIN
        question_practice_detail qpd 
    ON
        up.device_id = qpd.device_id
    JOIN
        question_detail qd
    ON
        qd.question_id = qpd.question_id
    WHERE
        up.university = '浙江大学'
)t1
GROUP BY
    difficult_level
ORDER BY
    correct_rate 
ASC