题解 | #获得积分最多的人(三)#

select b.user_id,u.name,b.grade_num
from
(select user_id,sum(if(type='add',grade_num,-1*grade_num)) grade_num 
from grade_info
group by user_id) b
left join
user u
on b.user_id=u.id
where b.grade_num in (
    select max(distinct a.grade_num)
    from
    (select user_id, sum(if(type='add',grade_num,-1*grade_num)) grade_num 
    from grade_info
    group by user_id) a
)
order by b.user_id

• 利用sum和if函数求得用户的当前得分
• 求最大值
• 连接user表