题解 35 | #浙大不同难度题目的正确率#

【场景】：不同条件下的情况 【分类】：分组查询、select if

分析思路

难点：

1.不同难度可以理解为每个难度

浙大每个难度题目下的正确率

• [使用]： count(if(result = 'right', 1, null))和group by difficult_level

求解代码

方法一： from 表连接

select
    difficult_level,
    count(if(result = 'right', 1, null))/count(a.device_id) as correct_rate
from user_profile a, question_practice_detail b, question_detail c
where a.device_id = b.device_id
and b.question_id = c.question_id
and university = '浙江大学'
group by difficult_level
order by correct_rate

方法二：

join 表连接

select
    difficult_level,
    count(if(result = 'right', 1, null))/count(a.device_id) as correct_rate
from user_profile a
join question_practice_detail b using(device_id)
join question_detail c using(question_id)
where university = '浙江大学'
group by difficult_level
order by correct_rate