积分最高：先连接一下，单行数据加减分情况，id分组，求和(取分数等于最高分的--或者排序=1的，不能用limit取最大值有点麻烦)

/select id,name,grade_num,type
from user join grade_info on ueser.id=user_id/

select id,name,grade_sum from
(select id,name,sum(grade_numif(type='add',1,-1)) as grade_sum
from grade_info join user on user.id=user_id
group by id) as A
group by id
having grade_sum in (select max(grade_sum) from (select id,name,sum(grade_numif(type='add',1,-1)) as grade_sum
from grade_info join user on user.id=user_id
group by id) as A)