with t as (
    select user_id, sum(grade) as grade
    from (
        select user_id,
        case when type='add' then grade_num else -grade_num end as grade
        from grade_info
    ) temp
    group by user_id
)
select id, name, grade as grade_num
from (
    select user_id, grade, dense_rank() over (order by grade desc) as dr
    from t
) temp join user on temp.user_id=user.id
where dr=1
order by id