Quote from one of the replies in the mentioned Quiz:
--------------- “…My friend Louis Davidson argues that it’s better to make the foreign key not null and add a row to the lookup table to represent the Does-Not-Apply value. I see that as a surrogate lookup and would prefer the null.“ [“Microsoft SQL Server 2008 Bible” by Rolf Nielsen]
---------- So, if the above quote is correct, it means the great authority in Database Design suggests to avoid NULL usage for FKs.
Yeah, but I'm sure someone will find fault with the grammar. <s>
