sql server set complex constraints

1CREATE FUNCTION dbo.fnIsAddressOwner (
2  @CustomerId int,
3  @AddressId int
4)
5RETURNS tinyint
6AS
7BEGIN
8  DECLARE @Result tinyint
9  IF EXISTS(SELECT * FROM CustomerAddresses WHERE CustomerId=@CustomerId and AddressId=@AddressId)
10    SET @Result= 1
11  ELSE 
12    SET @Result= 0
13  RETURN @Result
14END
15
16
17CREATE TABLE Customers (
18  CustomerId int,
19  PreferredAddressId int,
20  CONSTRAINT ckPreferredAddressId CHECK (
21    dbo.fnIsAddressOwner(CustomerId, PreferredAddressId) = 1)
22  )
23)
24