Another mysql_num_rows() problem from newb :(

Hi Guys,

I searched the forum but couldnt seem to figure it out for myself due to me not using sql before

A friend of mine made a database which was linked to WBB permissions. now I'm trying to get it to work with vbulletin but getting the error :

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource .

here is the code

if ($HTTP_COOKIE_VARS['XXX'] && $HTTP_COOKIE_VARS['XXX']) {
$userid = $HTTP_COOKIE_VARS['XXX'];
$a1 = mysql_db_query($phpdb,"SELECT * FROM XXX WHERE userid = '$userid'");
if (mysql_num_rows($a1) == 1) {
$cpass = mysql_result($a1,0,"XXX");
if ($cpass == $HTTP_COOKIE_VARS['XXX']) {
$username = strtolower(mysql_result($a1,0,"XXX"));

Ok, I feel this is what you want to do with the script:
1. check if the two cookies are set.
2. If set, you want to use the values stored in those cookies(Eg: username and passwords) to run some query.

Now what I feel is that to check if the cookie is set, you may use the inbuilt isset() function.
More info about isset() at tizag.com/phpT/phpsessions.php