Necesito sacar el outliers de la varibale monto que esta en venta.Utilizando el método Tres Sigmas aplicado por Producto

SELECT product, avg(amount) as promedio, stddev(amount) as desviacion, avg(amount) + 3 * stddev(amount) as umbral_superior, avg(amount) - 3 * stddev(amount) as umbral_inferior

FROM sales
GROUP BY product