group by和distinct

Question

select university,distinct（difficult_level）,count(question_id )/count(distinct（device_id）) avg_answer_cnt
from question_practice_detail
join user_profile u on q.device_id=u.device_id
join question_detail on q.question_id = question_detail.question_id
group by university

我就想问不group by difficult_level，在select 里面distinct可以吗？？

Answer 1

distinct是可以直接取不一样的数据，但是你的sum count聚合函数需要配合group by使用呀