Re: So what's null then if it's not nothing?

On 17 Nov 2005 14:41:19 -0800, michael_at_preece.net wrote:

>I didn't have to respond to this. If I hadn't you would never had known
>what I thought about your post. My response would not exist. What you
>would be reading here would have no value. It would have been an empty
>string. It would also have been unknown.

Hi Mike,

I'm not sure if it will survive past all filters, but I just posted an empty message in reply to this message. I hit the reply button, selected the complete quoted text, hit Delete, then clicked the post button (oh, I just realize I should have temporarily disabled my automatic signature as well - please just PRETEND that there's no signature either, okay?)

I did NOT write a reply to Alfredo's post.

If you check your news reader, you should be able to see the difference between my empty post to you, and the lack of any post by me to Alfredo.

If a database can't distinguish between these two categories, it's unfit to be used for representation of Usenet discussions. (And for a whole lot of other applications as well).

>You will say that at the logical level something can exist - in that it
>is part of a set - and yet have an unknown value. You would, presumably
>- also say that it does not necessarily have a value equal to empty
>string, because it's unknown. In order to record that "fact" you (or
>the SQl engine) have/has to store some code at the physical level to
>say it's not an empty string - it's null. It's not though is it? It's
>whatever you stored to represent "unknown".

It is *REPRESENTED* by whatever was chosen to *REPRESENT* the absence of a value. Don't confuse representation by what is represented.

My first name is represented by a series of four numbers on most computers. The numbers used on an ASCII machine will differ from those on an EBCDIC machine. But that doesn't make the name any different.

-1 represented in binary 1's complement is the same value as -1 represented in binary 2's complement - even though not all bits in the representation are the same.

HOW a Null is represented is irrelevant. WHAT it represents is what matters.

Best, Hugo

-- 

(Remove _NO_ and _SPAM_ to get my e-mail address)