nulls and three value logic by C.J. Date


Summary: beware of nulls, they can surprise you

So far, this one is the best out of the five in the series.

nulls are painfull in db world. No matter how you define them (null, unknown, nothing at all). You can always use something that means – “missing value” – let it be: “sysmiss”, 999, “NULL”, 0. But there is still a problem. And that’s the purpose of this video, to show you how nulls can mess around with your data. You will learn how to become more suspicious in terms of results that you get from sql queries involving nulls.

Pay attention that this video will not provide you with definite answer on how to solve the problem of nulls. It is nither the sql tutorial. It’s rather a smoke sign indicating the problem.

There is, however one remark that make me think “come on, that’s not the proper way of giving the argument”. When C.J. Date discusses arguments against null defenders he jumps into “maybe” logic which stands in quite contradiction to what he defends over the whole course of the lecture.

Anyway, definitely worth watching.

Product page:

O’Reilly (video): Nulls, Three-Valued Logic, and Missing Information