SQL DELETE

DELETE FROM ... WHERE

SELECT COUNT(*) AS before FROM orders;
DELETE FROM order_items WHERE order_id IN (SELECT order_id FROM orders WHERE status = 'cancelled');
DELETE FROM orders WHERE status = 'cancelled';
SELECT COUNT(*) AS after FROM orders;

before
12

after
11

Like UPDATE, a DELETE without WHERE removes every row. Run the same WHERE as a SELECT first.

Foreign keys

You can't delete a row that other rows still reference when foreign keys are enforced — delete the children first, or declare ON DELETE CASCADE.

TRUNCATE and soft deletes

• TRUNCATE TABLE t (PostgreSQL, MySQL) quickly empties a whole table.
• Many apps use soft deletes — a deleted_at column — so data can be restored and audited.