Idempotency in a DB

Idempotency is another important topic after the ACID properties.
Idempotency means:
Performing the same operation multiple times should give the same result, not duplicate effects.

Scenario: Duplicate Transfer

I ran the same transfer twice:

~ First transfer

UPDATE accounts SET balance = balance - 200 WHERE name = 'Christina';
UPDATE accounts SET balance = balance + 200 WHERE name = 'Sharon';

~ Same transfer again (duplicate)

UPDATE accounts SET balance = balance - 200 WHERE name = 'Christina';
UPDATE accounts SET balance = balance + 200 WHERE name = 'Sharon';