CASCADE

Learn how a child table reacts when the parent changes.

FOREIGN KEY

With FOREIGN KEY you link a column to another table's primary key. It keeps referential integrity.

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(id)
);

Orders.customer_id references customers.id.

The table orders is created.

FOREIGN KEY blocks adding an order for a non-existent customer. ON DELETE decides what happens when the customer is removed.

Create orders with id INT PRIMARY KEY and customer_id INT FOREIGN KEY REFERENCES customers(id).

Show example solution

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(id)
)

Add relation

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  ____ (customer_id) REFERENCES customers(id)
);

Show answer

CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  FOREIGN KEY (customer_id) REFERENCES customers(id)
);