Hola.
Para la 1.4, productos sin combinaciones:
select po.id_product AS id_pro, po.reference AS referencia, pol.name AS productname, po.price AS unitcost,po.on_sale AS rebajas, po.id_tax_rules_group AS id_tax, ptx.rate AS tax, po.price+po.price*ptx.rate/100 as PVP from ps_product po INNER JOIN ps_product_lang pol ON po.id_product = pol.id_product INNER JOIN ps_tax ptx ON ptx.id_tax = po.id_tax_rules_group where pol.id_lang =3;
Un saludo.