SELECT COUNT(DISTINCT Package)
    FROM Customer.Product;

    SELECT MIN(Id), MAX(Id)
    FROM Customer.Product
    WHERE is_discontinued = 'T';

    SELECT AVG(Highest_Elevation), avg(Lowest_Elevation) from World.Continent;

    SELECT COUNT(*)
    FROM World.City c1
    JOIN World.Country c2
    ON c1.Country_Code = c2.Code
    WHERE c2.Continent = 'North America';