Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: So what's null then if it's not nothing?

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@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 - 15:48:43 CST

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US