Обсуждение: deletion and many-to-one

If you have a many-to-one relationship, such as a contact list where
several people
share an address, you may want to delete the child record once the last
reference to
it is gone. I don't see how to implement a reference-counting scheme in
a database.
What's the right way to accomplish this?

On Sat, 9 Aug 2003, Jennifer Vargas wrote:

> If you have a many-to-one relationship, such as a contact list where
> several people
> share an address, you may want to delete the child record once the last
> reference to
> it is gone. I don't see how to implement a reference-counting scheme in
> a database.
> What's the right way to accomplish this?

Probably a trigger on update or delete of the referencing table.  If
you're not worried about some of the multi-session concurrency problems,
it's a marginally simple plpgsql trigger.