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

Bob Badour <bbadour_at_pei.sympatico.ca> writes:
> How is null easier than not inserting anything into an actual
> departures relation?

re:
http://www.garlic.com/~lynn/2006q.html#22 3 value logic. Why is SQL so special?

you have a row entry for a specific flight that has fields for scheduled and actual departures and arrival ... possibly with provision for computed values (difference between scheduled and actual).

or possibly you have two different tables ... one with scheduled flights and another with actual flights. an entry isn't inserted in the table of actual flights until the flight has actually happened.

the absence of a row in the actual flight table takes the place of null value fields (for not yet known information) in the table of specific flights. two tables then possibly involves referential integrity if there is an attempt to match an actual flight against a scheduled flight (in two different tables).

there is also, always the possibility that you might have an unscheduled actual flight ... an unplanned flight for which there hadn't been a (pre-)scheduled departure/arrival ... but for which there is actual departure ... with initially a projected arrival (as opposed to a scheduled arrival) ... and then eventually an actual arrival. Received on Mon Sep 11 2006 - 14:19:49 CDT