RE: Counterquestion - is Oracle a He or a She - or an It or a hermaphrodite
- From: "Leandro Guimaraes Faria C. Dutra" <ldutra@xxxxxxxxxxxxx>
- To: charlottejanehammond@xxxxxxxxx
- Date: Tue, 2 Aug 2005 09:52:45 -0300
oracle-l-bounce@xxxxxxxxxxxxx gravou em 2005-08-02 08:48:42:
> If you have, say, graduation dates for students and
> some students drop-out and do not complete their
> courses, you cannot set the "empty date" for their
> graduation - there is no such thing - even though you
> KNOW that they do not have a graduation date.
The conceptually correct way would be to have a relation of
students, and a separate one for graduates (as in subtyping). They are
not exactly the same thing, so modelling them in the same relation is a
conceptual error. This should have been caught also when checking the
model for spurious NULLable columns.
As Date, Darwen & McGoveran love to point, ultimately there are so
many possible non-values that you'd need several king of NULLs. 3VL is
complex enough, but Codd's proposal would need 4VL, and even 5VL has been
proposed if memory does not fail me. So the real solution is to stop
going down that way of madness and revert to what mainframe people have
been doing all along in sequential files, namely special values; only that
an RDBMS should enable us to define our own special values instead of
relying on contraptions such as all zeros or all nines or 4000-01-01...
It is a good time investment to read Date, Darwen, McGoveran,
Pascal etc. No Oracle support yet, not even ISO SQL, but if we don't know
what to ask for we'll never get it.
--
Leandro Guimarães Faria Corcete DUTRA
Administrador de Bases de Dados +55 (11) 4390 5383
Toyota do Brasil Ltda ldutra@xxxxxxxxxxxxx
São Bernardo do Campo, SP BRASIL
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