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Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that of Date&Darwin? [M.Gittens]

Re: Does Codd's view of a relational database differ from that of Date&Darwin? [M.Gittens]

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Fri, 10 Jun 2005 09:42:28 +0200
Message-ID: <MPG.1d1362b946561e4e98968f@news.ntnu.no>


In article <AC5qe.11727$F7.5746_at_news-server.bigpond.net.au>, hobbit_at_southern_seaweed.com.op says...
> >> And x + NULL does not evaluate to NULL but x.
> >
> > I should have mentioned that I am talking about the SQL2 standard (or
> > SQL/92 or SQL:1992 or SQL-92 or whatever it is called). I am not
> > familiar with MS TSQL.
>
> It appears to be an ISO/ANSI SQL standard. SQL-99:

What does NULL + NULL evaluate to? NULL or 0?

How about the sum of an attribute of an empty relation? Or of a column with just NULLs?

How about NULL - NULL? And NULL = NULL? Is x = y and x - y = 0 equivalent (x and y being integer range variables)?

If you evaluate x + 0, will you get 0 if x is NULL, but x if it is not?

-- 
Jon
Received on Fri Jun 10 2005 - 02:42:28 CDT

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