Do-while loop hangs the connection to website - php

Question

I am trying to use do-while loop to check if a value exists in database,
function check($a) {
$query = "SELECT * FROM `table` WHERE code = '$a'";
$result = mysql_query($query);
$nm = mysql_num_rows($result);
if ($nm > 0) {
return true;
} else {
return false;
}
}
function randomnumber() {
$chars = "abcdefghijkmnopqrstuvwxyz023456789";
srand((double)microtime()*1000000);
$i = 0;
$pass = '' ;
while ($i <= 10) {
$num = rand() % 33;
$tmp = substr($chars, $num, 1);
$pass = $pass . $tmp;
$i++;
}
return $pass;
}
$number = randomnumber();
do { $number = randomnumber(); } while (!check($number));
That codes somehow hangs the connection to website. After i execute this page, strangely it cannot connects to website until i restart the browser.
What may cause this ?

Answer 1

your query is never evaluating to true, so the loop is infinite. As long as it's not pulling back any rows where code = 'yourRandomNumber', then you will be looping indefinitely.

Answer 2

If you want to simply select a random 'code' from your database this code will be much more efficient than what you've got.
$query = 'SELECT DISTINCT code FROM `table`';
$result = mysql_query($query);
$my_arr = array();
while($row = $mysql_fetch_assoc($result)) {
$my_arr[] = $row['code']
}
$random_key = $my_arr[array_rand($my_arr)];
Re-reading your question and comments I'm less and less sure what your code originally set out to accomplish, if you could be a bit more clear on your objective here we could probably give you some advice on how to accomplish your goal more efficiently.
Edit:
This code will retrieve all of the codes already used in your table, calculate the difference from the possible codes, and then return one random unused code. No loop required. [well one loop, but it's a short one]
$psbl_codes = str_split("abcdefghijkmnopqrstuvwxyz023456789");
$query = 'SELECT DISTINCT code FROM `table`';
$result = mysql_query($query);
$used_codes = array();
while($row = $mysql_fetch_assoc($result)) {
$used_codes[] = $row['code']
}
$unused_codes = array_diff($psbl_codes, $used_codes);
echo "random unused code: " . $unused_codes[array_rand($unused_codes)];