with t1 as(
    select id,name,sum(case when type = "add" then grade_num else -grade_num end) grade_num
    from 
    user join grade_info on user.id = grade_info.user_id
    group by id,name
    order by id
)
select id,name,grade_num
from t1
where grade_num = (
    select max(grade_num) from t1 
)