UPDATE and DELETE

Change and remove

UPDATE changes columns in rows that match WHERE; DELETE removes matching rows. Both use RETURNING too:

UPDATE books SET price = price * 1.10
WHERE genre = 'poetry'
RETURNING title, price;

DELETE FROM reviews WHERE stars < 3 RETURNING id;

Note you can't DELETE a book that an order still references — the foreign key protects it. The database refuses to orphan the order_items rows that point at it. That's referential integrity doing its job.