Listing 4: Incremental Update
WITH LastDay AS
(
  SELECT
    GROUPING_ID(
      custid, empid,
      YEAR(orderdate), MONTH(orderdate), DAY(orderdate) ) AS grp_id,
    custid, empid,
    YEAR(orderdate) AS orderyear,
    MONTH(orderdate) AS ordermonth,
    DAY(orderdate) AS orderday,
    SUM(qty) AS qty
  FROM dbo.Orders
  WHERE orderdate = '20080419'
  GROUP BY
    CUBE(custid, empid),
    ROLLUP(YEAR(orderdate), MONTH(orderdate), DAY(orderdate))
)
MERGE INTO dbo.MyGroupingSets AS TGT
USING LastDay AS SRC
  ON     (TGT.grp_id    = SRC.grp_id)
     AND (TGT.orderyear  = SRC.orderyear
          OR (TGT.orderyear IS NULL AND SRC.orderyear IS NULL))
     AND (TGT.ordermonth = SRC.ordermonth
          OR (TGT.ordermonth IS NULL AND SRC.ordermonth IS NULL))
     AND (TGT.orderday   = SRC.orderday
          OR (TGT.orderday IS NULL AND SRC.orderday IS NULL))
     AND (TGT.custid   = SRC.custid
          OR (TGT.custid IS NULL AND SRC.custid IS NULL))
     AND (TGT.empid    = SRC.empid
          OR (TGT.empid IS NULL AND SRC.empid IS NULL))
WHEN MATCHED THEN
  UPDATE SET
    TGT.qty += SRC.qty
WHEN NOT MATCHED THEN
  INSERT (grp_id, custid, empid, orderyear, ordermonth, orderday)
  VALUES (SRC.grp_id, SRC.custid, SRC.empid, SRC.orderyear, SRC.ordermonth, SRC.orderday);