with re as(
select *,
       sum(g.grade_num) as grade_sum
from user as u
join grade_info as g
on u.id = g.user_id
group by id
order by grade_sum desc)

select re.id,
       re.name,
       re.grade_sum
from re
where re.grade_sum in(
select max(grade_sum) as grade_max from re);