select 客户,日期,sum(价格),avg(均价) 
from 表一 
where 日期>'2012-01-01'
 group by 客户,日期

------解决方案--------------------

SQL code
if object_id('[TB]') is not null drop table [TB]
go
create table [TB] (价格 int,均价 int,客户 nvarchar(2),日期 datetime)
insert into [TB]
select 20,2,'b','2012/1/1' union all
select 10,4,'b','2012/1/1' union all
select 5,1,'c','2012/1/1' union all
select 30,3,'a','2012/1/2' union all
select 10,1,'a','2012/1/2' union all
select 10,1,'c','2012/1/3' union all
select 15,1,'a','2012/1/3' union all
select 20,1,'a','2012/1/3'

select * from [TB]


SELECT CONVERT(VARCHAR(10),日期,120) AS 日期,客户,SUM(价格) AS 价格,AVG(均价) AS 均价
FROM dbo.tb
GROUP BY CONVERT(VARCHAR(10),日期,120),客户
ORDER BY 日期,客户


/*
日期    客户    价格    均价
2012-01-01    b    30    3
2012-01-01    c    5    1
2012-01-02    a    40    2
2012-01-03    a    35    1
2012-01-03    c    10    1