Hi Helen,

thanks for your quick response.

> Sure you can. You can even have an RI action
> ON DELETE SET NULL
> to return the dependent row to a "pool of orphans" when the master row gets
> deleted.

I know about ON DELETE SET NULL.
I think I did not make myself perfectly clear - I think "nullable" was
not the correct word for what I mean.

I would like to have a foreign key field that can be NULL - and when
it is NULL, no RI should take place.
But when the value is different then NULL, RI should take place and
deletes and updates should *not* be possible - i. e.
ON UPDATE NO ACTION and ON DELETE NO ACTION.
But a foreign key field defined like that does not accept NULLs.
This is my problem ;-)


Christian