题解 | #计算25岁以上和以下的用户数量#

#用if函数的写法

SELECT IF(age>=25,"25岁及以上","25岁以下") AS age_cut,count(device_id) AS number

FROM user_profile

GROUP BY age_cut;

#联合查询

SELECT "25岁以下" as age_cut,count(device_id) as number

FROM user_profile

WHERE age<25 OR age IS null

UNION ALL

SELECT "25岁及以上" as age_cut,count(device_id) as number

FROM user_profile

WHERE age>=25

#case

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(device_id) as number

FROM user_profile

GROUP BY age_cut