select name,sum(grade_num) as grade_sum from
grade_info left join user on
grade_info.user_id = user.id
where grade_info.user_id in (
select t1.user_id from (
select g1.user_id,sum(g1.grade_num) as grade_sum_1
from grade_info as g1
group by g1.user_id order by grade_sum_1 desc limit 1)t1 )
group by name