How can I test an UPDATE statement for example to see if it would work, for example if it would actually update rows etc?
Is there a way to simulate it easily?
Use a transaction to wrap your update statement and a select query (to test the update) and then always roll it back.
Example:
BEGIN;
UPDATE accounts SET balance = balance - 100.00
WHERE name = 'Alice';
SELECT balance FROM accounts WHERE name = 'Alice';
ROLLBACK; -- << Important! Un-does your UPDATE statement above!
A transaction typically ends with a commit but since you're just testing and do not want the changes to be permanent you will just roll back.