If you have a PEOPLE table and some birthdates are unknown, then remove the "birthdate" column and make another table called PEOPLE_BIRTHDATES with a "birthdate" column and a foreign key pointing to PEOPLE. Now your queries can have lots of left joins. The results will still have nulls, however.

Which is the reason why you shouldn't write outer joins.

So if we don't know the customer's birthdate we can't serve her? I can imagine a problem with that...

Sigh.

Where have I said any such thing ?

If there's no row for the customer in the joined table, the customer won't show up in an inner join.

Great. Now if you can explain to me where you got the idea that a join (inner or otherwise) is the only possible way to query two tables then we might get somewhere. Because you can also just do two queries. And no, that does not necessarily mean "two roundtrips to the DBMS" (which I know perfectly well is undesirable). There are techniques for avoiding that. Perhaps not in SQL, but that's a reason you should be pressing the vendors to improve SQL. Not for you to agree to the status quo of sticking with the vendors' old bypasses-and-hacks cheating bag.

Haha OK then use a UNION... oh wait we're gonna have NULLs with that too. One suspects you'll also have some vague objection to this point, but if the only way to address that is to wait on somebody to invent an "improved" SQL, one won't worry about it too much.

That "improved SQL" was already defined in the previous century, and has been implemented as well. Your ignorance drips off of every word you write.

E.F. Codd literally designed null into the relational model. I don't think calling someone ignorant is very helpful.

But the demeaning ridicule that gets thrown at me is ?

(BTW I doubt very much that "Codd designed null into the RM". Even his 12 rules mention only "a systemic way to deal with missing information", not "null".)

> What do you use in a database when you have a field where you literally do not know what the value should be?

You don't.

If a value may not be present for an entity, it's not an attribute of the entity in question, it's an attribute of another entity that has a (0..1):1 relationship to the entity in question.

Normalization eliminates NULL.

That's great. Now I do a query. Maybe I use a join. If a row has the "0" case of that (0..1):1 relationship, what do I get?

Or maybe I don't do a join. Maybe I do a separate query. If the query comes back with zero rows, then I... what?

What do I get ? You get what you ask for.

Then I ... what ? Then you do what needs to be done as specified by the business in the case the queried piece of information is unknown.

> What do I get ? You get what you ask for.

In the join case, don't I get a NULL in the row that comes back if there isn't an entry in the other table? Or do I just not get a row?

> Then you do what needs to be done as specified by the business in the case the queried piece of information is unknown.

Sure, but how do I represent that condition in my software? With a different class/structure? With a flag that indicates that the other field isn't valid? Or with a null?

From where I sit, normalization doesn't make the problem go away at all.