select name, sum_g grade_num
from (
    select user_id, sum(grade_num) sum_g, max(sum(grade_num))over() max_sum_g
    from grade_info
    where type = 'add'
    group by user_id, type
) t1
join user u
on t1.user_id = u.id
where sum_g = max_sum_g;