SELECT  CAST(DT.CalendarYear AS INT) * 100 + CAST(DT.WeekNumberOfYear AS INT) AS WeekNummer,
        SUM(FIS.OrderQuantity) AS AantalOrders,
        SUM(FIS.SalesAmount) AS Omzet
FROM    FactInternetSales AS FIS
        LEFT OUTER JOIN DimTime AS DT ON FIS.OrderDateKey = DT.TimeKey
WHERE ProductKey = 1
AND DT.CalendarYear > 2001
GROUP BY ALL CAST(DT.CalendarYear AS INT) * 100 + CAST(DT.WeekNumberOfYear AS INT)
ORDER BY CAST(DT.CalendarYear AS INT) * 100 + CAST(DT.WeekNumberOfYear AS INT)