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

From: Hugo Kornelis <hugo_at_pe_NO_rFact.in_SPAM_fo>
Date: Sun, 20 Nov 2005 21:12:39 +0100
Message-ID: <spl1o1luvcu0pfmlp3g8l6agr4ahglqdgr@4ax.com>


On Sun, 20 Nov 2005 14:30:37 +0000, Bernard Peek wrote:

>In message <ltdvn1dd5k2cdqthb9s5jjsihpgf9lvsdj_at_4ax.com>, Hugo Kornelis
><hugo_at_pe_NO_rFact.in_SPAM_fo> writes

(snip)
>>A better example would be:
>>
>>What's the age (in whole years) of my dog?
>
>OK, so what is it's age (in whole numbers)?

Hi Bernard,

Ah, but that's exactly the point. I won't tell you the age of my dog. I won't even tell you if I have a dog at all - and if I have, then how many.

Since nobody here knows (except me, and I'm not telling), nobody will be able to answer. So there won't be an answer.

If the asnwer had to be stored in a relational database, the solution would be to bypass the INSERT statement. But what if several disjunct facts were combined into one table? What if the table has three columns: name (primary key), age_of_dog, and number_of_cats.

Since I have four cats, you'll have to insert a row, with Hugo Kornelis in the name column, four in the number_of_cats column, and the answwer to the above question in the age_of_dog column.

That's where NULL comes in. Had there been no number_of_cats columns, then there wouldn't have been any row at all. Now there is - and the NULL is used that there still is no answer to the question about my dog's age.

Best, Hugo

-- 

(Remove _NO_ and _SPAM_ to get my e-mail address)
Received on Sun Nov 20 2005 - 14:12:39 CST

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