如何对每一行进行累乘和累除

IF OBJECT_ID('TEMPDB.DBO.#tb') IS NOT NULL DROP TABLE #tb

GO

CREATE TABLE #tb

(

userid  VARCHAR(4),

trading  DATETIME,

rt  float

)



insert into #tb

values('0001','2012-12-01',0.3),

('0001','2012-12-02',0.6),

('0001','2012-12-03',0.4),

('0001','2012-12-04',0.8),

('0002','2012-11-01',0.5),

('0002','2012-11-02',0.5),

('0002','2012-11-03',0.6)

我想生成两个新列，一个是累计乘，一个是累计除，如下所示：
userid trading                                  rt       commulative_multiply     commulative_division
0001 2012-12-01 00:00:00.000 0.3     0.3                                        0.3
0001 2012-12-02 00:00:00.000 0.6     0.3*0.6                                 0.3/0.6
0001 2012-12-03 00:00:00.000 0.4     0.3*0.6*0.4                          0.3/0.6/0.4
0001 2012-12-04 00:00:00.000 0.8     0.3*0.6*0.4*0.8                   0.3/0.6/0.4/0.8
0002 2012-11-01 00:00:00.000 0.5     0.5                                         0.5
0002 2012-11-02 00:00:00.000 0.5     0.5*0.5                                  0.5/0.5
0002 2012-11-03 00:00:00.000 0.6     0.5*0.5*0.6                           0.5/0.5/0.6


上面累计乘法和累计除两列列举的公式是我所要表达的意思，实际中需要的是每一行按上述公式运算后的结果。
------解决方案--------------------

CREATE TABLE tb

(userid VARCHAR(4),

 trading DATETIME,

 rt float)

 

insert into tb

values

('0001','2012-12-01',0.3),

('0001','2012-12-02',0.6),

('0001','2012-12-03',0.4),

('0001','2012-12-04',0.8),

('0002','2012-11-01',0.5),

('0002','2012-11-02',0.5),

('0002','2012-11-03',0.6)





-- 累计乘函数

create function dbo.fn_multiply

(@u varchar(4),

 @t datetime) returns float

as

begin

 declare @x float

 

 select @x=1.0

 

 select @x=@x*rt

  from tb

  where userid=@u and trading<=@t



 return @x

end





-- 累计除函数

create functi