On 2 Feb 2007, at 20:21, A. Pagaltzis wrote:
* Zbigniew Lukasiak <[EMAIL PROTECTED]> [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.)
Or by using a delayed FK and inserting into all of them during a
transaction.
Unless you're using MySQL, which doesn't support this because it's a
fucking toy (insert relational dildo management system joke here).
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.
Pretty much. Supporting more complex -relations- ala m2m is cool, but
they're a different beast.
--
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