Re: Unique Keys
From: Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net>
Date: Fri, 26 Nov 2004 07:00:40 -0500
Message-ID: <8gij72-46a.ln1_at_pluto.downsfam.net>
> such:
> unique
> simple
>
> Yes, but only by subverting the traditional meaning of "equals"! So
> what do you do now if you want to know if the 2 DATEINTERVALs really
> are the same?
>
Date: Fri, 26 Nov 2004 07:00:40 -0500
Message-ID: <8gij72-46a.ln1_at_pluto.downsfam.net>
Tony Andrews wrote:
>> I would suggest it is more useful to define the equality operator as
> such:
>> >> where x = (a,b) >> and y = (c,d) >> >> x = y iff (a <= c <= b) OR (a <= d <= b) >> >> It is the equality operator definition that makes it a declarative
> unique
>> constraint exactly the same as any other, and also makes possible
> simple
>> foreign keys. Now we have: >> >> CREATE TABLE reservations ( >> hotel_room char(4), >> span DATEINTERVAL ) >> PRIMARY KEY (hotel_room,span)
>
> Yes, but only by subverting the traditional meaning of "equals"! So
> what do you do now if you want to know if the 2 DATEINTERVALs really
> are the same?
>
Perhaps you would be more comfortable with the OO term? Operator
Overloading?
--
Kenneth Downs
<?php $sig_block="Variable scope? What's that?";?>
Received on Fri Nov 26 2004 - 13:00:40 CET