;with t1 as 
(
    select row_number() over (partition by [业务员] order by [业绩] desc) as R,
            [业务员],[客户],[业绩] from [表]
)t2 as 
(
    select [业务员],[客户],[业绩] from t1 where  r <=10
)
select * from t2 /*前10名 客户*/

--剩下的楼主自己解决吧

------解决方案--------------------
http://topic.csdn.net/u/20090406/21/d801c681-3187-42f3-ab1a-caa9124a9074.html?67857