Listing 1: Script to Create and Populate the Customers and Orders Tables
USE tempdb
GO
IF OBJECT_ID('Orders') IS NOT NULL
  DROP TABLE Orders
GO
IF OBJECT_ID('Customers') IS NOT NULL
  DROP TABLE Customers
GO
CREATE TABLE Customers
(custid  varchar(5)  NOT NULL PRIMARY KEY,
  city    varchar(10) NOT NULL,
  /* other columns */)

SET NOCOUNT ON
INSERT INTO Customers(custid, city) VALUES('A', 'Seattle')
INSERT INTO Customers(custid, city) VALUES('B', 'Seattle')
INSERT INTO Customers(custid, city) VALUES('C', 'Seattle')
INSERT INTO Customers(custid, city) VALUES('D', 'Denver')

CREATE TABLE Orders
(orderid int        NOT NULL PRIMARY KEY,
  custid  varchar(5)     NULL REFERENCES Customers,
  /* other columns */)

INSERT INTO Orders(orderid, custid) VALUES(1, 'A')
INSERT INTO Orders(orderid, custid) VALUES(2, 'B')
INSERT INTO Orders(orderid, custid) VALUES(3, 'B')
INSERT INTO Orders(orderid, custid) VALUES(4, 'B')
INSERT INTO Orders(orderid, custid) VALUES(5, NULL)
GO