I've found it's easier just to keep things NULL in many cases. Sure, if you have a student database with the column favorite_sport, maybe it makes sense to use

I've found it's easier just to keep things NULL in many cases. Sure, if you have a student database with the column favorite_sport, maybe it makes sense to use the value "Not a sports fan." But think about an email list with the column unsubscribe_date. For active recipients, you'll want that field to be NULL.