SQL - rentabilidad de un cliente en tablas distintas

-- euros gastados

SELECT pro.preu * dc.quantitat

FROM poructes pro inner join detall_comandes dc

on pro.codi = dc.producte

--cantidad de compras

SELECT cli.id_client, count(co.numero)

FROM cli.clients inner join comandes co

on cli.id_client = co.numero

GROUP BY cli.id_client

SELECT clients.nif, clients.nom, clients.cognoms,

(SUM(productes.preu * detall_comandes.quantitat)  / 

(SELECT COUNT(comandes.numero)

		FROM clients AS clients1 INNER JOIN comandes ON clients1.id_client = comandes.client

        WHERE clients1.id_client = clients.id_client

        GROUP BY clients1.id_client)) AS rentabilitat

FROM clients INNER JOIN comandes ON clients.id_client = comandes.client

	INNER JOIN detall_comandes ON comandes.numero = detall_comandes.comanda

	INNER JOIN productes ON detall_comandes.producte = productes.codi

GROUP BY clients.nif, clients.nom, clients.cognoms, clients.id_client

ORDER BY rentabilitat DESC;