assertion and company

["snake84\(at)inwind\(dot)it" <snake84(at)inwind(dot)it>]

oh, i 'm sorry, i've given you a blank mail :P

i begin to say: Sorry for my bad english ^^


My problem is:
i have 2 tables,"editoriale" and "ColaboratoreFisso", in the first i have the foreign key of the second and in this last table i have an attribute named MembroCR that can assume only boolean values...

Now, i have to be sure that every row in "ColaboratoreFisso", that has the key also inside "editoriale", has the attribute MembroCR=TRUE.

So i thought to resolve this with an Assertion, but postgresql doesn't implement it... in what way i can solve my matter?

This is my code (my first database, so don't blame me if i have writed too much mistakes :P)

CREATE TABLE editoriale (
	CodiceE serial PRIMARY KEY,
	Titolo varchar(100) NOT NULL,
	Testo text NOT NULL,
	MembroComitatoRedazione char(16) NOT NULL,
	FOREIGN KEY (MembroComitatoRedazione) REFERENCES collaboratoreFisso (CodiceFiscaleF)
           ON DELETE CASCADE ON UPDATE CASCADE);

     CREATE ASSERTION CONTROLLO_COMITATO
            CHECK (NOT EXISTS
			( SELECT MembroComitatoRedazione
			  FROM editoriale
			  WHERE MembroComitatoRedazione IN
				(SELECT CodiceFiscaleF
				 FROM collaboratoreFisso
				 WHERE MembroCR = FALSE)));


if you can write me an alternative soulution^^



ANOTHER QUESTION:

I have some problem with my redundancies:

In what way i can implement them? With triggers? I have tried but my code doesn't work, i don't know how to use them :(


Thanks for your help! ^^