Foreign Key Constraints

Let's look at this in the context of a primary key. When this primary key is referenced by a column in another table, this primary key becomes the foreign key of the other table. For example, consider the previously created database PACKT_ONLINE_SHOP:

DROP DATABASE IF EXISTS PACKT_ONLINE_SHOP;
CREATE DATABASE IF NOT EXISTS PACKT_ONLINE_SHOP;
USE PACKT_ONLINE_SHOP;
CREATE TABLE Customers
(
    CustomerID INT NOT NULL AUTO_INCREMENT,
    FirstName CHAR(50) NOT NULL,
    LastName CHAR(50) NOT NULL,
    Address CHAR(250) NULL,
    Email CHAR(200) NULL,
    Phone CHAR(50) NULL,
    Notes VARCHAR(750) NULL,
    BalanceNotes VARCHAR(750) NULL,
    PRIMARY KEY (CustomerID)
);
CREATE TABLE Orders
(
    OrderID INT NOT NULL AUTO_INCREMENT,
    ...