database design - Nullable Foreign Key bad practice?

Question

Let's say you have a table Orders with a foreign key to a Customer Id. Now, suppose you want to add an Order without a Customer Id, (whether that should be possible is another question) you would have to make the foreign key NULL... Is that bad practice or would you rather work with a link table between Orders and Customers? Although the relationship is 1 to n, a link table would make it n to n. On the other hand, with a link table, I don't have those NULLS anymore...

There won't actually be a lot of NULL's in the database, because a record with a foreign key to NULL is just temporarily until a customer for the order is added.

(In my case it isn't an Order and a Customer).

EDIT: What about a unassigned Customer to link to?

Answer 1

No There is nothing wrong with Nullable FKs. This is common when the entity the FK points to is in a (zero or one) to (1 or many) relationship with the primary Key referenced table.

An example might be if you had both a Physical address and a Mailing address attribute (column) in a table, with FKs to an Address table. You might make the Physical address nullable to handle when the entity only has a post office box (mailing address), and the mailing address nullable to handle when the mailing address is the same as the physical address (or not).