select id,name,grade_num
from 
(select user_id, dense_rank() over(order by grade_num desc) t_rank,grade_num
from 
(select user_id,sum(grade_num)grade_num from grade_info group by user_id)r1)r2 
join user u
on r2.user_id=u.id
where t_rank=1
order by id