different between PhP_self and REQUEST_URI ???

[DMonster]

i just made a feedback form and testing it :
- when the people fill in the form correct then the information will send to my database but if that person keep refreshing or f5 the page the information will keep sending without submit ..... afterward, I tried to change the action ['php_self'] to ['request_uri'] and it worked the form stopped repeating its self when people keep refreshing the page.
-can any1 explain why this happened and what is the different between ['php_self'] and ['request_uri']?
thanks for any help..

[anakadote]

For one, I believe REQUEST_URI only works on Apache and not IIS. Are you on a Windows server perhaps? And you can trying echoing the value of both to see what the difference is:

<?php

echo $_SERVER['PHP_SELF'].'<br /><br />';
echo $_SERVER['REQUEST_URI'];

?>