SELECT date_trunc('month', date_commande) AS numero_mois, round(SUM(prix_unitaire*quantite), 2) AS montant_total FROM commandes JOIN lignes_commandes USING (numero_commande) WHERE date_commande >= to_date('01/01/2010', 'DD/MM/YYYY') AND date_commande < to_date('01/01/2015', 'DD/MM/YYYY') GROUP BY 1 ORDER BY 1;
