题解 | #浙大不同难度题目的正确率#

SELECT c.difficult_level,SUM(IF(result='right',1,0))/COUNT(result) AS correct_rate
FROM user_profile AS a,question_practice_detail AS b,question_detail AS c
WHERE a.university='浙江大学'
AND a.device_id=b.device_id
AND b.question_id=c.question_id
GROUP BY c.difficult_level
ORDER BY correct_rate