Fundamentals · Easy · Free
What is a foreign key? How does referential integrity work?
FresherFundamentalsDatabase Fundamentals
Foreign keys
sql
CREATE TABLE orders (
id INT PRIMARY KEY,
customer_id INT NOT NULL,
FOREIGN KEY (customer_id) REFERENCES customers(id)
);Referential integrity blocks orphan orders when customer deleted—ON DELETE CASCADE/SET NULL policies matter.
Explain CASCADE carefully—can surprise in prod.