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