题解 | #SQL35 浙大不同难度题目的正确率#

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