Subtotalen en SQL

Kijk eens naar iets als

DECLARE @Sales TABLE(
        CUS_ID  INT,
        PRODUCT VARCHAR(20),
        AMOUNT FLOAT
)
INSERT INTO @Sales SELECT 12,'A', 2.50 
INSERT INTO @Sales SELECT 12,'B', 5.80 
INSERT INTO @Sales SELECT 24,'A', 10.00 
INSERT INTO @Sales SELECT 24,'B', 30.00

;WITH Vals AS (
        SELECT  cus_id, 
                product, 
                amount,
                1 DisplayOrder,
                SUM(amount) OVER(PARTITION BY cus_id) OrderTotal
        FROM    @Sales 
        UNION ALL   
        SELECT  cus_id, 
                'Total' AS product, 
                SUM(amount),
                2 DisplayOrder,
                SUM(amount)
        FROM    @Sales 
        GROUP BY cus_id
)
SELECT  cus_id,
        product,
        amount
FROM    Vals
ORDER BY  OrderTotal DESC,cus_id,DisplayOrder, product