Here is a small example of using MERGE from the Katmai Books On Line
MERGE FactBuyingHabits AS fbh
USING (SELECT CustomerID, ProductID, PurchaseDate FROM PurchaseRecords) AS src
ON (fbh.ProductID = src.ProductID AND fbh.CustomerID = src.CustomerID)
WHEN MATCHED THEN
UPDATE SET fbh.LastPurchaseDate = src.PurchaseDate
WHEN NOT MATCHED THEN
INSERT (CustomerID, ProductID, LastPurchaseDate)
VALUES (src.CustomerID, src.ProductID, src.PurchaseDate);
Cross-posted from SQLBlog! - http://www.sqlblog.com/