RE: Useful Oracle books - C.J. Date theory vs. practicality

the "IS NULL" operator is a great operator to check for attributes for being
NULL,
no problem. that's the only thing it's supposed to do ;-) and it is purely
two-valued.

your suggestion is a nice "work around", and you could even write it more
condensed by using functions like COALESCE and CASE expressions to handle
the UNKNOWN case caused by null=values.

my only point (somewhere at the beginning of this thread :-) was that
certain seemingly obvious logical equivalences don't hold in three-valued
logic.

and I guess it is hard to make your workaround generic -- what if the
<condition> is constructed dynamically, at run time, and can e.g. be a
compound predicate with some ANDs and ORs?
then your "outer IF" becomes almost impossible to generate...

Cheers,
Lex.

---------------------------------------------
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 Nuno Souto
Sent: Saturday, May 29, 2004 08:57
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Useful Oracle books - C.J. Date theory vs. practicality


Lex de Haan said,on my timestamp:29/05/2004 5:29 PM:

> the IS NULL operator is two-valued,
> so it would never show the "desired" behavior for this experiment...
> 'string' IS NULL always evaluates to FALSE, and '' IS NULL evaluates to
TRUE
> (which is quite unfortunate, but that's another discussion)

I see your point, of course.  Otherwise it's harder to show the problem.

But the thing that bugs me is: isn't the Oracle (and presumably
others db) solution of "IS NULL" a good solution?

I mean: avoid the TRUE/FALSE/NULL logic problem without re-defining the
entire IF?

Is there something wrong with:
IF (<var> is NOT NULL) then
   IF(<var> = 'something') then do_this
   ELSE do_that
   END IF;
ELSE do_nothing;
END IF;
other than the obvious verbosity/style of writing?

(says he who had to code something like this ad-infinitum in a
project 3 years ago...)
--
Cheers
Nuno Souto
in sunny Sydney, Australia
dbvision@xxxxxxxxxxxxxxx
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