Re: 3 value logic. Why is SQL so special?

Paul wrote:
> 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?

you're kidding right?

>
> (Personal work experience). Aircraft. Flight Schedules.
>
> Dep time,
> Arr 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.

So an aircraft might not take off and yet it has a departure time attribute? That makes absolutely no sense at all.

>
>
> Paul...
>
>
>
> --
>
> plinehan __at__ yahoo __dot__ __com__
>
> XP Pro, SP 2,
>
> Oracle, 9.2.0.1.0 (Enterprise Ed.)
> Interbase 6.0.1.0;
>
> When asking database related questions, please give other posters
> some clues, like operating system, version of db being used and DDL.
> The exact text and/or number of error messages is useful (!= "it didn't work!").
> Thanks.
>
> Furthermore, as a courtesy to those who spend
> time analysing and attempting to help, please
> do not top post.
Received on Mon Sep 11 2006 - 20:36:28 CEST