Transactions and ACID Properties

ACID explained

• Atomicity: all operations succeed or none do.
• Consistency: constraints remain valid after commit.
• Isolation: concurrent transactions do not corrupt each other.
• Durability: committed data survives crashes.

Transfer money safely

Financial and inventory systems rely on transactions so partial updates never leak into user-visible state.

BEGIN;

UPDATE accounts
SET balance = balance - 500
WHERE account_id = 101;

UPDATE accounts
SET balance = balance + 500
WHERE account_id = 202;

COMMIT;
-- If anything fails, ROLLBACK;