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
union all
select
  "25岁及以上" as age_cut,
  count(device_id)
from
  user_profile
where
  age >= 25;
# 题意要求写法 ：
SELECT
  CASE
    WHEN age < 25
    or age is null THEN '25岁以下'
    WHEN age >= 25 THEN '25岁及以上'
  END age_cut,
  count(*)
from
  user_profile
group by
  age_cut ;
# 网友写法 ：
SELECT
  if(
    age < 25
    OR age IS null,
    "25岁以下",
    "25岁及以上"
  ) as age_cut,
  count(u.device_id) as number
FROM
  user_profile as u
GROUP BY
  age_cut