--EXAMPLE OF A UPDATE FUNCTION WITH TRIGGER PLPGSQL

CREATE OR REPLACE FUNCTION update_aumentarpreco ()
    RETURNS TRIGGER
    LANGUAGE PLPGSQL
    AS 
    $BODY$
BEGIN
    IF NEW.ps_availqty = 2 THEN
        NEW.ps_supplycost = OLD.ps_supplycost * 0.10;
        RETURN NEW;
    END IF;
    RETURN NULL;
END;
$BODY$ 

CREATE TRIGGER update_aumentarpreco
    BEFORE UPDATE OF ps_availqty ON partsupp
    FOR EACH ROW
    EXECUTE PROCEDURE update_aumentarpreco ();