ajax error handling / show error if mysql result is false? - php

Question

I have a form where a user can input a voucher code:
<form>
<input type="text" name="promo" id="promo">
<div class="promo_check"></div>
</form>
the user can click on my div 'promo_check' which runs the following ajax:
<script type="text/javascript">
$(document).ready(function() {
$(document).on('click', '.promo_check', function() {
var promo = $("#promo").val();
$.ajax({
type: "POST",
url: "process_promo.php",
data: {data:promo},
success: function(data)
{
window.alert(data);
}
});
});
});
</script>
this then executes my mysql query to check if the voucher exists in the database and that the $_SESSION['user_name'] / i.e. the logged in user has the permission to use that voucher.
process_promo.php:
<?php
$username = "mark";
$password = "password";
$hostname = "localhost";
//connection to the database
$dbhandle = mysql_connect($hostname, $username, $password)
or die("Unable to connect to MySQL");
$_SESSION['username'] = 'mark';
$promo = $_POST['data'];
$query = "SELECT * FROM hewden1.supplier_users WHERE promo_code = '$promo'";
$result = mysql_query($query) or die(mysql_error());
while($row = mysql_fetch_assoc($result)) {
if (mysql_num_rows($result) > 0) {
if ($row['user_name'] == $_SESSION['username']) {
echo 'correct';
}else{
if ($row['user_name'] !== $_SESSION['username']) {
echo 'not correct for user';
} }
}else{
echo 'error';
}
}
?>
this all works fine, if the voucher code matches for that user then it echo's 'correct' and my ajax will show an alert saying 'correct'. Then if the voucher code does not match for the user then it echo's 'not correct for user'.
The problem i have is when the voucher is not valid at all and cannot be found in the database it is suppose to echo 'error' however ajax show a blank/empty alert message instead of showing 'error'.
I think this is because i am using success: in my ajax but when i try to add an error: call back my script stops working. can someone please show me what i'm doing wrong? thanks in advance

Answer 1

Looking at process_promo.php, if you get no result from the database query, then the contents of the while loop never get executed. Putting it another way, inside the while loop you'll never have a mysql_num_rows($result) == 0 condition.
Here I moved your while loop inside your mysql_num_rows check:
if (mysql_num_rows($result) > 0) {
while($row = mysql_fetch_assoc($result)) {
if ($row['user_name'] == $_SESSION['username']) {
echo 'correct';
}
else {
if ($row['user_name'] !== $_SESSION['username']) {
echo 'not correct for user';
}
}
}
}
else {
echo 'error';
}
...which also pulls the error report outside the while loop and gives it a chance to execute.