Re: So what's null then if it's not nothing?
Date: 25 Nov 2005 09:00:33 -0800
So any attribute can store a "value" outside its intended domain? I
thought you mentioned earlier that NULL is an empty set - is it
> Well Jon - I'd say they're both NULL. NULL is type-less.
So any attribute can store a "value" outside its intended domain? I thought you mentioned earlier that NULL is an empty set - is itactually of type E, where E consists of the empty set?
> In the case of
> "no value at all" for an integer variable we can't store an empty
> string so we would store NULL.
This makes no sense in other domains either - what about "NULL dates"? What sort of date manipulations (e.g. "same date next month") can one do on it?
> I know a lot of educated people will
> tell me that NULL, when compared to any other value, results in
> Unknown. I'd agree - if I agreed that NULL was unknown - or missing -
> or absent - or not, in fact, data. I believe that NULL is, correctly,
> "no value at all".
I keep reading this, over and over, and it still makes no sense. Can you define some semantics of a null when it occurs in a date attribute, a string attribute, an integer or real attribute, custom typed (e.g. "object") attributes? How do they "behave" in the presence of operations over the attribute's domain?
> We store something on a database because we know
> something. We can know something is empty.
Maybe if you define "empty." Does "empty" mean the same as "no value at all"? "Empty" isn't any more helpful than "NULL" to me.
So why is it in the DB?
So we know the existence of something non-existent? I've just read a large chunk of this discussion, and have seen nothing but tail-chasing so far. Can you define, with any precision, the semantics of a "NULL value"?