/*EXAMPLE OF A UPDATE FUNCTION WITH TRIGGER PLPGSQL*/

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

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

/*DROP TRIGGER update_aumentarpreco ON partsupp*/
/*Testing

UPDATE
    partsupp
SET
    ps_availqty = 4
WHERE
    ps_suppkey = 2*/