Re: pro- foreign key propaganda?

"David Cressey" <cressey73_at_verizon.net> wrote in message news:ZxeYj.3653$Uf1.3359_at_trndny08...
>
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:PseYj.9097$nl7.5836_at_flpi146.ffdc.sbc.com...
>>
>> "David Cressey" <cressey73_at_verizon.net> wrote in message
>> news:RkTXj.2139$Zy1.1952_at_trndny05...
>> >
>> > "jonniesavell" <jsavell_at_gmail.com> wrote in message
>> >
> news:9e62cc4a-4e40-4cf5-9503-2bd77e0ddf46_at_x19g2000prg.googlegroups.com...
>> >>
>> >> > I think you are confusing foreign keys with declarative referential
>> >> > integrity. Foreign keys are a must and I'm sure your database uses
>> >> > them.
>> >> > What you are talking about (and I agree) is a constraint.
>> >>
>> >> OK. I am stupid. I thought that an instance of declarative referential
>> >> integrity in DDL create a foreign key between one or two tables in the
>> >> database.
>> >>
>> >
>> > Not stupid. Just ignorant. The wonderful thing about ignorance is
>> > that
>> > it
>> > can be cured. Read up on the subject, as others have suggested.
>> >
>> > The above argument is about definitions.
>> >
>> >
>> >> What's the difference?
>> >
>> > If I say "select * from orders inner join order_detail
>> > on orders.order_no = order_detail.order_no;
>> >
>> > then order_details.order_no must be a "foreign key" regardless of
>> > whether
>> > it was declared as such in DDL.
>> >
>> > If in the above case, order_details.order_no is for some strange
>> > reason
>> > NOT
>> > a foreign_key reference to the corresponding row in orders, then you
> are
>> > the victim of a sadistic and perverse database designer. Or perhaps
> just
>> > a
>> > supremely ignorant one.
>> >
>>
>> I think you're mistaken, David.
>
> Go back and read my comment again.
>
>>A foreign key constraint is a database
>> constraint that guarantees that whenever there is a row in a referencing
>> table, there is one and only one row in the table it references.
>
> I know that, and you should know by now that I know that.
>

I know that you know, and I know that you know that I know that you know, but I don't know that everyone else knows what we both know--especially since the above argument is about definitions :-)

> A foreign key and a foreign key constraint are not the same thing.

That's a new one on me. What's the difference? Received on Mon May 19 2008 - 19:55:06 CEST