USE Northwind
GO

SELECT CustomerID, SUM(Freight)-SUM(ShipVia) 
  FROM Orders
 WHERE CustomerID = 'VICTE'
GROUP BY CustomerID
GO

INSERT INTO Customers(CustomerID) SELECT 'Brett'
GO

INSERT INTO Orders(CustomerID)
SELECT 'Brett'
GO

SELECT CustomerID, SUM(ISNULL(Freight,0))-SUM(ISNULL(ShipVia,0)) 
  FROM Orders
 WHERE CustomerID = 'BRETT'
GROUP BY CustomerID
GO

SELECT CustomerID, SUM(ISNULL(Freight,0))-SUM(ISNULL(ShipVia,0)) 
  FROM Orders
 WHERE CustomerID = 'xBRETT'
GROUP BY CustomerID
GO

DELETE FROM Orders WHERE CustomerID = 'Brett'
GO

DELETE FROM Customers WHERE CustomerID = 'Brett'
GO

    SELECT xxx.CustomerID, SUM(ISNULL(Freight,0))-SUM(ISNULL(ShipVia,0)) 
      FROM (SELECT 'xBrett' AS CustomerID) AS XXX
 LEFT JOIN Orders o
	ON XXX.CustomerID = o.CustomerID
  GROUP BY xxx.CustomerID
GO