题解 | 计算男生人数以及平均GPA

# 解法一（常规思路）
select
    count(1) as male_num,
    round(avg(gpa), 1) as avg_gpa
from
    user_profile
where
    gender = 'male';

# 解法二（条件聚合）
select
    count(case when gender= 'male' then 1 else null end) as male_num,
    round(avg(case when gender= 'male' then gpa else null end), 1) as avg_gpa
from
    user_profile;