题解 | #浙大不同难度题目的正确率#

/*  不同难度 考虑分组 GROUP BY difficult_level
浙江大学的情况 WHERE university = '浙江大学'
答题正确率 = 正确数/总数


 */
SELECT difficult_level,
SUM(CASE WHEN result='right'THEN 1 ELSE 0 END)/COUNT(qpd.question_id) 
AS correct_rate
FROM question_practice_detail qpd 
LEFT JOIN  user_profile up 
ON qpd.device_id = up.device_id
LEFT JOIN question_detail 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 ;