Transactions & ACID

Transactions group operations that must succeed or fail together.

Transfer money between accounts:

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

ACID properties:

• Atomicity - all or nothing
• Consistency - rules always enforced
• Isolation - transactions don't interfere
• Durability - committed = permanent

If anything fails, ROLLBACK undoes everything.

Critical for: banking, e-commerce, any financial data.