Transactions and ACID Properties

The Problem

I was transferring money between accounts. What if the debit succeeded but the credit failed? The money would disappear!

Wrap multiple statements in a transaction. If anything fails, everything is rolled back.

BEGIN;

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

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

COMMIT; -- Or ROLLBACK if something goes wrong

**Atomicity**: All or nothing.

**Consistency**: Data stays valid.

**Isolation**: Transactions don't interfere.

**Durability**: Once committed, it's permanent.

*Day 87: Isolation Levels Explained.*