php mysql invitation code for registration form

Question

I would really appreciate once again if someone could help me out! I'm working on a registration form which works fine, but I wanted to implement an invitation code check in there, too.

I never did that before and since I'm a newbie I just searched for a solution, tried to understand and to adopt...so please don't judge me :) I'm just trying to learn with each step!

So quick what I'm trying to do ->

1. user types in an invitation code 2.if incorrect (checked in the database then -> error msg)
2. if correct (checked in database -> then gets used)
3. code database gets updated that the code is not usable anymore

here is my code:

$invite_code = ($_POST['invite_code']);
// Validate invite code
if (empty($_POST['invite_code'])) {
$err7 = "Wrong invitation code";
}  
//check if invitation code is valid in the database and not already taken
$rs_check = mysql_query("SELECT `code` from tableinvitecodes WHERE '$invite_code' 
AND `taken` = '0'") or die (mysql_error()); 
$num = mysql_num_rows($rs_check);
// Match row found with more than 0 results  - the code is invalid. 
if ( $num <= 0) { 
$err7 = "Invite code is invalid";
}
else {
$invite_code = $_POST['invite_code'];
}

what's not workin is the check for the "being used already", it gets updated in the database..that's working fine. The mistake must be the checking but I don't know how to connect it with the "if (empty($_POST['invite_code']))..." :-/

Thanks in advance for your help!

and that part works! ->

//set approved code to 1 to block that code
if(empty($err7)) {
$rs_invite_code = mysql_query("update tableinvitecodes set `taken` = '1' WHERE 
code='$invite_code' ") or die(mysql_error());
}

Answer 1

It looks like your query is mal-formed. You have:

SELECT `code` from tableinvitecodes WHERE '$invite_code' AND `taken` = '0'

I think you should have something like:

SELECT `code` from tableinvitecodes WHERE <<SOMETHING HERE>> = '$invite_code' AND `taken` = '0'