Mysql 获取成绩排序后的名次

select id,maxScore,(@rowNum:=@rowNum+1) as rowNo
from t_user,
(select (@rowNum :=0) ) b
order by t_user.maxScore desc 

select u.rowNo from (
select id,(@rowNum:=@rowNum+1) as rowNo
from t_user,
(select (@rowNum :=0) ) b
order by t_user.maxScore desc ) u where u.id="2015091810371700001";