Foreign Key Constraint

Overview

A Foreign Key maintains referential integrity between two tables by linking a column to a Primary Key in another table.

Learning Objectives

• Link relational tables using FOREIGN KEY ... REFERENCES.
• Prevent orphan records and enforce cascading actions (ON DELETE CASCADE).

Code Examples

SQL

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT REFERENCES customers(customer_id) ON DELETE CASCADE
);

Summary

Foreign Keys enforce referential integrity between parent and child tables.