SELECT materials.customer, DatePart("yyyy",[purchasedate],7) & DatePart("ww",[purchaseDate],7) AS YearWeekNumber, Sum(materials.extended) AS SumOfMatl
FROM materials
WHERE materials.customer=[Forms]![SelectCustBobsWeekly].[simcust]
GROUP BY materials.customer, DatePart("yyyy",[purchaseDate],7)...