I am checking the validation of the request with an if query, if ($request_userid == $userid) { ... } Thats working as expected. But further testing has shown, that if $request_userid or $userid is 0 or "", then the condition is true and the script runs the if query but it shouldn't. I am currently solving it with: if ($userid == "" ) { exit ("exit"); } But I don't think that this is the right way? Can you explain why it doesn’t work with the if query and what would be the correct way to check it?