Referential integrity

Learn referential integrity with FOREIGN KEY.

Referential integrity ensures a foreign key points to a row in another table.

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

Orders.customer_id → customers.id.

The table orders is created.

Referential integrity — details

A foreign key cannot point to a non-existent value. Deletes or updates can be restricted.

For example, if an order is inserted with a customer_id that doesn't exist in customers, the FOREIGN KEY stops it with an error.

Add a FOREIGN KEY on customer_id in orders.

Show example solution

ALTER TABLE orders
ADD CONSTRAINT fk_customer
FOREIGN KEY (customer_id) REFERENCES customers(id)

FOREIGN KEY

CONSTRAINT fk_customer ____ (customer_id) REFERENCES customers(id)

Show answer

CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(id)