Design question : Nullable FK & FK To Unique Key

Hi gurus,

Our Invoice may or may not has Orders before it. User can input order and produce invoice from it, OR they can just input Invoice without order. So we plan to have Nullable FK on Invoice.

The question is :

1. What is the bad side of Nullable FK ?
2. FK from Invoice to Orders , not refering to PK , but to the Unique Key of the Orders, what is the bad side of this ?

Thank you for your help,
xtanto Received on Thu Nov 09 2006 - 07:07:08 CST