Web Listing 9: Query with NOT EXISTS Returning Desired Results
SELECT DISTINCT Country, Region, City
FROM dbo.Employees AS E
WHERE NOT EXISTS
  (SELECT * FROM dbo.Customers AS C
   WHERE (C.Country = E.Country
          OR (C.Country IS NULL AND E.Country IS NULL))
     AND (C.Region = E.Region
          OR (C.Region IS NULL AND E.Region IS NULL))
     AND (C.City = E.City
          OR (C.City IS NULL AND E.City IS NULL)));