Grupowanie SQL według miesiąca i roku

SELECT CAST(MONTH(date) AS VARCHAR(2)) + '-' + CAST(YEAR(date) AS VARCHAR(4)) AS Mjesec, SUM(marketingExpense) AS SumaMarketing, SUM(revenue) AS SumaZarada 
FROM [Order]
WHERE (idCustomer = 1) AND (date BETWEEN '2001-11-3' AND '2011-11-3')
GROUP BY CAST(MONTH(date) AS VARCHAR(2)) + '-' + CAST(YEAR(date) AS VARCHAR(4))

Lub jak wspomniał @40-Love, możesz rzucać z wiodącymi zerami:

GROUP BY 
  CAST(YEAR(date) AS VARCHAR(4)) + '-' + right('00' + CAST(MONTH(date) AS VARCHAR(2)), 2)