SQL—group by和count函数、where筛选

题目：求每个学校(university)每种性别(gender)的用户数、30天内平均平均活跃天数(active_days_within_30)和平均发帖数量(question_cnt)。

我的尝试：

select count(device_id) as user_num,

round(AVG(active_days_within_30),1) as avg_active_day,

round(AVG(question_cnt),1) as avg_question_cnt,

from user_profile

where group by university and gender

错误点（暂时发现的）：

1、语法错误where和group by连用是不对的，删掉where

2、越界数组行为(虽然不知道牛客咋判定的越界，但是我没觉得我越界了（气壮！）)：看了讨论区，在select后面加了个university和gender，又出现了越界行为（喵喵喵的！）要删掉and。

敲！还要注意顺序，答案：

select

gender,

university,

count(device_id) as user_num,

round(AVG(active_days_within_30),1) as avg_active_day,

round(AVG(question_cnt),1) as avg_question_cnt,

from user_profile

group by gender,university