题解 | #浙大不同难度题目的正确率#

浙大不同难度题目的正确率 http://www.nowcoder.com/practice/d8a4f7b1ded04948b5435a45f03ead8c

SELECT
    t3.difficult_level,
    (SUM(if(t2.result='right',1,0)) / COUNT(t2.result)) as correct_rate
FROM    
    user_profile t1,
    question_practice_detail t2,
    question_detail t3
WHERE
    t1.university = '浙江大学'
    and t1.device_id = t2.device_id
    and t2.question_id = t3.question_id
GROUP BY 
	t3.difficult_level
ORDER BY 
	correct_rate ASC;