What is a Transaction?

A transaction is a unit of work that is either fully completed or fully rolled back.

ACID Properties:

  • Atomicity: All operations succeed or none
  • Consistency: Database remains valid before and after
  • Isolation: Transactions don't interfere
  • Durability: Once committed, it stays

Example:

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