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

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,
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.

Paul...

-- 

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