# Transactions — MySQL

Source: https://www.geekswithgeeks.com/en/mysql/sql-transactions

> Group statements so they succeed or fail together.

## ACID, briefly

**ACID** — Atomicity, Consistency, Isolation, Durability — describes the guarantees a transaction gives you.

## BEGIN, COMMIT, ROLLBACK

Wrap related statements between `START TRANSACTION` and `COMMIT`; `ROLLBACK` undoes everything since the start if something goes wrong.

```sql
START TRANSACTION;
UPDATE accounts SET balance = balance - 500 WHERE id = 1;
UPDATE accounts SET balance = balance + 500 WHERE id = 2;
COMMIT;
```

## Why it matters

Without a transaction, a crash between the two `UPDATE`s above would leave money **deducted from one account but never added to the other**.