题解 | #计算25岁以上和以下的用户数量#

/*
select
'25岁以下' as age_cut,
count(device_id)
from
user_profile
where
age < 25
or age is null
group by
age_cut
union
select
'25岁及以上' as age_cut,
count(device_id)
from
user_profile
where
age >= 25
group by
age_cut
 */
/*
select
if (age >= 25, '25岁及以上', '25岁以下') as age_cut,
count(1)
from
user_profile
group by
age_cut;
 */
select
    (
        case
            when age >= 25 then '25岁及以上'
            when age < 25
            or age is null then '25岁以下'
        END
    ) as age_cut,
    count(1)
from
    user_profile
group by
    age_cut;

熟悉if和case when的使用。