FOREIGN KEY with cascade example --- sql server

IF OBJECT_ID('SalesHistory') > 0
DROP TABLE SalesHistory
GO
CREATE TABLE SalesHistory
(
SaleID int IDENTITY(1,1) NOT NULL,
ProductID TINYINT,
CustomerID INT,
SaleDate datetime NULL,
SalePrice money NULL,
CONSTRAINT pk_SaleID PRIMARY KEY (SaleID)
)
GO
IF OBJECT_ID('Customers') > 0
DROP TABLE Customers
GO
CREATE TABLE Customers
(
CustomerID INT,
FirstName VARCHAR(50),
LastName VARCHAR(50),
CONSTRAINT pk_CustomerID PRIMARY KEY (CustomerID)
)
GO
IF OBJECT_ID('Products') > 0
DROP TABLE Products
GO
CREATE TABLE Products
(
ProductID TINYINT,
ProductDescription VARCHAR(100),
CONSTRAINT pk_ProductID PRIMARY KEY (ProductID)
)
GO
ALTER TABLE SalesHistory
ADD CONSTRAINT fk_SalesHistoryCustomerID FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID) ON DELETE SET NULL ON UPDATE SET NULL
ALTER TABLE SalesHistory
ADD CONSTRAINT fk_SalesHistoryProductID FOREIGN KEY (ProductID) REFERENCES Products(ProductID) ON DELETE CASCADE ON UPDATE CASCADE
go
delete  from Customers
INSERT INTO Products (ProductID, ProductDescription)
SELECT 1, 'BigScreen'
UNION ALL
SELECT 2, 'Computer'
UNION ALL
SELECT 3, 'PoolTable'
GO
INSERT INTO Customers(CustomerID , FirstName , LastName )
SELECT 1, 'Jason', 'Tomes'
UNION ALL
SELECT 2, 'Chris', 'Robards'
UNION ALL
SELECT 3, 'Megan', 'Hill'
UNION ALL
SELECT 4, 'Wanda', 'Guthrie'
UNION ALL
SELECT 5, 'Lilly', 'Cunningham'
UNION ALL
SELECT 6, 'Amanda', 'Travis'
UNION ALL
SELECT 7, 'Willy', 'Grant'
UNION ALL
SELECT 8, 'Zach', 'Tacoma'
UNION ALL
SELECT 9, 'Marty', 'Smith'
UNION ALL
SELECT 10, 'Wendi', 'Jones'
UNION ALL
SELECT 11, 'Angie' , 'Corolla'
UNION ALL
SELECT 12, 'Shelly', 'Hartson'
GO
DECLARE @i SMALLINT
SET @i = 1
WHILE (@i <=100)
BEGIN
INSERT INTO SalesHistory(ProductID, SaleDate, SalePrice, CustomerID)
VALUES(1, DATEADD(mm, @i, '3/11/1919'), DATEPART(ms, GETDATE()) + (@i + 57), ((DATEPART(ms, GETDATE()) + (@i + 29)) % 12) + 1)
INSERT INTO SalesHistory(ProductID, SaleDate, SalePrice, CustomerID)
VALUES(2, DATEADD(mm, @i, '3/11/1927'), DATEPART(ms, GETDATE()) + (@i + 13), ((DATEPART(ms, GETDATE()) + (@i + 29)) % 12) + 1)
INSERT INTO SalesHistory(ProductID, SaleDate, SalePrice, CustomerID)
VALUES(3, DATEADD(mm, @i, '3/11/1908'), DATEPART(ms, GETDATE()) + (@i + 29), ((DATEPART(ms, GETDATE()) + (@i + 29)) % 12) + 1)
SET @i = @i + 1
END
go
select * from SalesHistory (nolock) where CustomerID = 100
select * from Customers (nolock) WHERE CustomerID = 100
DELETE FROM Customers
WHERE CustomerID = 3
begin tran
update Customers
set CustomerID = 100
where customerid=10
commit

select * from Products

DELETE FROM Products
WHERE ProductID = 3
update Products
set ProductID =4
WHERE ProductID = 3
select * from SalesHistory where ProductID = 3
truncate table SalesHistory