Re: 3 value logic. Why is SQL so special?
From: Paul <paul_at_see.my.sig.com>
Date: Mon, 11 Sep 2006 19:24:56 +0100
Message-ID: <mfabg2h28m5ts9laighrf0kl9so9kdqpei_at_4ax.com>
Date: Mon, 11 Sep 2006 19:24:56 +0100
Message-ID: <mfabg2h28m5ts9laighrf0kl9so9kdqpei_at_4ax.com>
Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
> > FWIW, I try to create subtypes
> > where there are no nulls.
> That's nice. I simply don't allow null in any database I design.
Why not?
(Personal work experience). Aircraft. Flight Schedules.
Dep time,
&c.
Scheduled_Departure_Time = 'DD:MM:YYYY 10:15'
Actual_Departure_Time = <null> untill we know different, then we put
in a value.
Otherwise you have to take account of the fact that these aircraft
took off in 9999 or else in 0001 or whatever.
Null is easier. The aircraft hasn't taken off yet, we don't know when
it will take off, or even if it will take off.
Arr time,
Paul...
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