Re: So what's null then if it's not nothing?
From: Hugo Kornelis <hugo_at_pe_NO_rFact.in_SPAM_fo>
Date: Wed, 30 Nov 2005 22:48:43 +0100
Message-ID: <937so1lmcudd6t2kfplu2i8bopgld12rtf_at_4ax.com>
Date: Wed, 30 Nov 2005 22:48:43 +0100
Message-ID: <937so1lmcudd6t2kfplu2i8bopgld12rtf_at_4ax.com>
On 29 Nov 2005 07:11:29 -0800, vc wrote:
(snip)
> The 3vl unknown is mapped to false
Hi vc,
The 3vl unknown isn't mapped to anything.
ANSI standard says:
- For SELECT: return rows if the condition in the WHERE clause evaluates
to true; omit rows if it evaluates to either false or unknown.
- For CONSTRAINT: accept rows if the constraint's condition evaluates to
true or unknown; reject rows if it evaluates to false.
No mappping involved.
>, therefore, null is
>*not* a duplicate.
You can't say that null is not a duplicate - it is unknown if it's a duplicate or not.
Best, Hugo
-- (Remove _NO_ and _SPAM_ to get my e-mail address)Received on Wed Nov 30 2005 - 22:48:43 CET