题解 | #分组计算练习题#

select 
gender,university,count(device_id) as user_num,avg(active_days_within_30
) as avg_active_day,avg(question_cnt) as avg_question_cnt 
from 
user_profile 
group by 
gender,university

确实很疑惑，为啥count(distinct device_id)就不对了呢