SELECT [Query1].[Année], [main].[Mois].[Mois_Text], Total,
[main].[Réglements].[Facture],
[main].[Réglements].[Date],
[main].[Réglements].[Montant]
FROM (SELECT
SUBSTR ([main].[Achats].[Date], 1, 4) AS Année,
SUBSTR ([main].[Achats].[Date], 6, 2) AS Mois,
SUM ([main].[Achats].[Montant]) AS Total
FROM [main].[Achats]
GROUP BY SUBSTR ([main].[Achats].[Date], 1, 4), SUBSTR ([main].[Achats].[Date], 6, 2)
ORDER BY SUBSTR ([main].[Achats].[Date], 1, 4), SUBSTR ([main].[Achats].[Date], 6, 2)) [Query1]
INNER JOIN [main].[Mois] ON [Query1].[Mois] = [main].[Mois].[Mois_Num]
FULL JOIN [main].[Réglements] ON [Query1].[Année] = [main].[Réglements].[Année]
AND [Query1].[Mois] = [main].[Réglements].[Mois]