Re: Useful Oracle books - C.J. Date theory vs. practicality
- From: "Binley Lim" <Binley.Lim@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 30 May 2004 02:14:43 +1200
From: "Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
> 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.
> 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...
/
I have written some complex PL/SQL routines (like parsing free-format
name/address lines). Had to use IF/AND/ORs and lots of brackets but never
came across an "impossible" case.
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.
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