20.1 Referential Integrity Defined

Referential Integrity ensures that the relationship between tables remains consistent. Specifically, it ensures that a value in the Foreign Key column of one table matches an existing value in the Primary Key column of the referenced (parent) table.

20.2 The FOREIGN KEY Constraint

A Foreign Key is a field in one table that refers to the Primary Key in another table.

Parent vs. Child Table

• Parent Table (Referenced): Contains the primary key being referred to (e.g., DEPARTMENT).
• Child Table (Referencing): Contains the foreign key (e.g., EMPLOYEE).

20.3 Referential Actions

What happens if you try to delete or update a record in the Parent table that is being referred to by a Child table?

20.4 Example Implementation

CREATE TABLE Orders (
    OrderID int PRIMARY KEY,
    CustomerID int,
    FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
    ON DELETE CASCADE
);