关于update的触发器，高手帮忙啊

我的目的是更新一个叶子结点的数量时，及时更新此结点所有父结点的价格，但是没有达到要求，不会更新，请各位大哥帮小弟看看，先谢过了
ALTER TRIGGER updatepricebynum
ON dbo.RealRationanalyse
FOR UPDATE
AS
if update(num)
begin
declare @num float(8)
declare @num1 float(8)
declare @price money
declare @balance float(8)
declare @marketprice money
declare @pid int
declare @parentid int
select @num=realrationanalyse.num from realrationanalyse,deleted where realrationanalyse.id=deleted.id

select @num1=inserted.num,@price=realrationanalyse.marketprice,@pid=realrationanalyse.parentid from realrationanalyse,inserted where realrationanalyse.id=inserted.id

set @balance=@num1-@num
set @balance=@balance*@price

select @marketprice=marketprice,@num=num from realrationanalyse where id=@pid

set @marketprice=@marketprice+@balance
--更新其父结点的市场价格
update realrationanalyse set marketprice=@marketprice where id=@pid

set @balance=@balance*@num
--一直往上查找其父结点，直到找到根结点为止
select @parentid=parentid from realrationanalyse where id=@pid

while(@parentid<>0)
begin
set @pid=@parentid
select @marketprice=marketprice,@parentid=parentid,@num=num from realrationanalyse where id=@parentid
update realrationanalyse set marketprice=@marketprice+@balance where id=@pid
set @balance=@balance*@num
end
end