Stop data inserting into a database twice

Question

I was wondering what methods/preventions other programmers use to stop data being entered twice into a MySQL database when a user refreshes on the same page as a form? Obvio

Answer 1

POE (Post Once Exactly) is an HTTP pattern aimed at warning the client to block double submits using a proprietary header ...

GET /posts/new HTTP/1.1
POE: 1
...

... but is still in specification.

http://www.mnot.net/drafts/draft-nottingham-http-poe-00.txt

I think the above nonce is a good solution. Though storing the nonce as a discrete session variable will introduce some errors if the client is attempting to perform simultaneous posts from multiple tabs. Maybe better to ...

$_SESSION['nonces'][] = $nonce;

... and ...

if (in_array($_POST['nonce'], $_SESSION['nonces'])) {

... to allow for multiple nonces (nonci? noncei?).