UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2;

BEGIN; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; COMMIT;

Without transaction, if second UPDATE fails, first UPDATE is permanent - money disappears! Transactions ensure both succeed or both fail. Critical for data integrity in financial operations.

Critical

BEGIN; UPDATE employees SET salary = salary * 1.1; -- Forgot to COMMIT

BEGIN; UPDATE employees SET salary = salary * 1.1; COMMIT;

Forgetting COMMIT means changes are not saved. When connection closes, changes are rolled back. Always explicitly COMMIT or ROLLBACK to make intent clear.

High