Analysis :: How To Right Choose Key Column In Mining Structure For Microsoft Analysis Services

How to right choose key column in"Mining Structure" for Microsoft Analysis Services?
 
I have table:

"Incoming goods"

Create table Income (         
ID int not null identity(1, 1)            
[Date] datetime not null,             
GoodID int not null,               
PriceDeliver decimal(18, 2) not null,               
PriceSalse decimal(18, 2) not null,               
CONSTRAINT PK_ Income PRIMARY KEY CLUSTERED (ID),             
CONSTRAINT FK_IncomeGood foreign key (GoodID)  references dbo.Goods ( ID )            
)

I'm trying to build a relationship(regression) between “Price Sale” from Good and “Price Deliver”.But I do not know what column better choose as “key column”: ID or GoodID ?