CREATE OR REPLACE FUNCTION aviso() RETURNS TRIGGER AS'

DECLARE
 min_fecha timestamp(3);
BEGIN

IF(new.pres_dev=="devuelta") THEN

    select new.numcinta from prestamos where new.numcinta in(select numcinta from cintas where titulo in(
        select titulo from lista_espera) and nomdirector in(select nomdirector from lista_espera));


END;
'LANGUAGE 'plpgsql';

DROP TRIGGER aviso ON prestamo;
CREATE TRIGGER aviso
    AFTER UPDATE ON prestamo
    FOR EACH ROW
    EXECUTE PROCEDURE aviso();