RE: Useful Oracle books - C.J. Date theory vs. practicality
- From: "Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Sat, 29 May 2004 21:44:20 +0200
see inline ...
Kind regards,
Lex.
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visit my website at http://www.naturaljoin.nl
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Binley Lim
Sent: Saturday, May 29, 2004 15:15
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Useful Oracle books - C.J. Date theory vs. practicality
> my only point (somewhere at the beginning of this thread :-) was that
> certain seemingly obvious logical equivalences don't hold in three-valued
> logic.
People who work with DBs that implement NULLs distinguish the difference
earlier on. Or they produce wrong results. Not sure what your theoritical
argument is. In practice, NULLs work. Do you have a theory that says they
should not? Something that does not work doesn't need a theory to say so -
it will crash and burn by itself.
LDH> NULLs would work much better if they would have been implemented
consistently...
LDH> But I agree they work, and as long as you know the pitfalls there is no
problem.
Within an Oracle context, I'm really quite puzzled to see someone suggesting
something like 'Mort subite' = NULL. You shoudl never, never equal" NULL. It
is a meaningless comparison -- noone writing Oracle code should be caught
dead writing 'something' = NULL.
LDH> I am afraid you missed the point -- obviously, I agree 'Mort subite' =
NULL
LDH> is a weird expression (although the beer with that name is not bad at
all.)
LDH> I only used it to manufacture a logical expression evaluating to
UNKNOWN;
LDH> Normally, you would write something like BEER_TYPE = 'Mort subite'
LDH> where BEER_TYPE is a column potentially containing NULL values;
LDH> for any row containing a NULL value, the effect would be the same.
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