SQL27 View user details of different age groups (niuke.com sql topic)

 wrong answer:

select  device_id,gender, case when age <20 then "20岁以下"
                             when age <=20 and age<=24 then "20-24岁"
                             when age >=25 then "25岁及以上"
                             when age is null then "其他"
                             end age_cut
FROM user_profile

correct answer:

select  device_id,gender, case when age <20 then "20岁以下"
                             when age between 20 and 24 then "20-24岁"
                             when age >=25 then "25岁及以上"
                             when age is null then "其他"
                             end age_cut
FROM user_profile

When judging the 20-24 stage, the result is incorrect when using age <=20 and age<=24,

But when using age between 20 and 24 the result is correct.