[dba-SQLServer] NULLs

So, what's the value of the unused field for each patient?

Susan H. 


> If I was designing that system, I would have two fields.  One is the SSN,
> the other is a unique hospital defined number for people without a SSN.
> Either could be Null, but one of them must be filled in correctly.  And
> neither could be a FK.