with
t1 as(
    select
        user_id,
        sum(grade_num) as grade_num
    from
        grade_info
    group by
        user_id
),
t2 as(
    select
        name,
        grade_num
    from
        t1 left join user on t1.user_id=user.id
    order by
        grade_num desc
    limit
        1
)

select * from t2