Re: 3 value logic. Why is SQL so special?
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Mon, 11 Sep 2006 18:48:24 GMT
Message-ID: <YbiNg.16497$9u.190748_at_ursa-nb00s0.nbnet.nb.ca>
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> Why not?
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> (Personal work experience). Aircraft. Flight Schedules.
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> Dep time,
> Arr time,
>
> &c.
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> Scheduled_Departure_Time = 'DD:MM:YYYY 10:15'
> Actual_Departure_Time = <null> untill we know different, then we put
> in a value.
>
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> Otherwise you have to take account of the fact that these aircraft
> took off in 9999 or else in 0001 or whatever.
Date: Mon, 11 Sep 2006 18:48:24 GMT
Message-ID: <YbiNg.16497$9u.190748_at_ursa-nb00s0.nbnet.nb.ca>
Paul wrote:
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> Bob Badour <bbadour_at_pei.sympatico.ca> wrote:
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>>> FWIW, I try to create subtypes >>>where there are no nulls.
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>>That's nice. I simply don't allow null in any database I design.
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>
>
> Why not?
>
> (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.
How is null easier than not inserting anything into an actual departures relation? Received on Mon Sep 11 2006 - 20:48:24 CEST