[Dbix-class] Re: Three table relationships?

[A. Pagaltzis]

* Zbigniew Lukasiak <zzbbyy at gmail.com> [2007-02-02 13:25]:
> select * from a, b, c where
> a.key1 = b.key2 and b.key1 = c.key2 and c.key1 = a.key2
> 
> With composed (key1, key2) primary keys for a, b and c tables.
> 
> This join is a three table relationship (just like the many to
> many case) - and I think it is not reducible to a superposition
> of two table relstionships (differently from the many to many
> case).

Heh. And unless you weaken your FK constraints, you will never be
able to insert a row into these tables. :P  (Except maybe with
some kind of multiple-table insert support, using a view or
whatever.)

> To reiterate - I did read your thesis that many to many is not
> a relatioship - so you don't need to repeat that - I am just
> asking why it is not and what is a relatioship.

I think a relationship is anything you can say in SQL DDL.

Regards,
-- 
Aristotle Pagaltzis // <http://plasmasturm.org/>