ON DELETE rule

I'm trying to do something like this:

CREATE RULE piezas_delete AS
ON delete TO piezas
DO update materia_prima set usadas=(usadas-1)
where n_material=old.n_material;

The rule is created. OK .... but the action doesn't run like it's supossed.
¿What is wrong?

Is "old" usable with "ON DELETE" rules ???

I think delete action its performed AFTER rule action .... ¿OK?
So ... it's possible to access field values of delete affectted registers?

--
Fernando Moyano

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