select
case when (select 1 from (select top 15 PERCENT 客户ID from 表 order by 销量 DESC,销售金额 DESC ) A where T.客户ID=A.客户ID)=1 then 'A'
when (select 1 from (select top 15 PERCENT 客户ID from 表 order by 销量,销售金额) A where T.客户ID=A.客户ID)=1 then 'C'
else 'B' end
from 表 T