CREATE OR REPLACE FUNCTION func_valor_cliente(id_cliente IN VARCHAR, ano IN NUMBER, mes IN NUMBER)
RETURN NUMBER
   IS valor_total NUMBER(11,2);
   BEGIN
        SELECT  dm.valor_total
            INTO valor_total
        FROM DebitoMensal dm
        WHERE   EXTRACT (MONTH FROM dm.ano_mes) = mes AND
        EXTRACT (YEAR FROM dm.ano_mes) = ano AND
        dm.id_cliente = id_cliente;

      RETURN(valor_total);

    END;