不能用left join 他会导致最后结果出现None
1 多表关联
2 正确答题/总答题数
3 将数据排序
select qud.difficult_level,sum(if(que1.result="right",1,0))/count(que1.result) as correct_cate from
(select
user.device_id,
university,
que.question_id,
que.result
from
user_profile as user
join (
select
device_id,
question_id,
result
from
question_practice_detail
) as que on user.device_id = que.device_id where university = "浙江大学" )
as que1
join
question_detail
as qud on que1.question_id=qud.question_id
group by qud.difficult_level
order by correct_cate asc