题解 | #浙大不同难度题目的正确率#

解题思路:

1. 正确率= 正确题目数/总题目数:correct_ret=sum(if(result='right', 1, 0))/ count(question_id)
2. 不同难度:group by difficult_level
3. 浙江大学:university='浙江大学'
4. 排序:order by correct_ret
5. 三个数据表需要相连接

select qd.difficult_level, sum(if(qpd.result='right', 1, 0))/ count(qd.question_id) correct_rate from user_profile up inner join question_practice_detail qpd on up.device_id=qpd.device_id right join question_detail qd on qpd.question_id=qd.question_idwhere university='浙江大学'group by qd.difficult_levelorder by correct_rate;