Normalization of an 1:1 or 1:0 relationship

Question

when using relation databases and you want 3NF (do you call it 3NF in english?), then you pull 1:1 relationsships together into one table. But what happens if the rationship

Answer 1

Third normal form basically means that an attribute (or column) depends on the key, the whole key and nothing but the key (so help me, Codd).

If you have an attribute which is either there or not there, that attribute itself may still follow the rules.

In those cases, I would simply keep the attributes in the main table and make them nullable to indicate whether or not they're appropriate for the row.

By way of (contrived) example, you may have a SocialSecurityNumber attribute as your primary key (I won't go into the arguments as to whether this is a good idea here or whether you should use a surrogate key since it's irrelevant to the question).

Further assume that you have a distinct BankAccount attribute for paying their wage into, and that you're not one of those nice employers that can distribute a wage to multiple bank accounts for the purpose of dodging taxes :-)

Now the bank account of someone is dependent entirely on the chosen key but not everyone may possess one (they may be paid in cash). In other words, a classic 1:0/1 case as you put it.

In that case, you would simply make the bank account number nullable in the table.