select
case when graduate_year = '2022' then '大四'
when graduate_year = '2023' then '大三'
when graduate_year = '2024' then '大二'
when graduate_year = '2025' then '大一'
end grade,
round(avg(gpa),2) as avg_gpa
from 
user_profile
group by grade
having grade is not null
order by avg_gpa desc

本地考察case when的用法，最后需要注意，要保证grade不为空。