function db_query( $q ) {
    global $dbg_qry_cnt;
    $dbg_qry_cnt++;
    $r = mysql_query( $q );
    if(mysql_error() != NULL)
        {
        die('<tt>'.$q.'</tt><br />caused an error:(br />'.mysql_error());
        }
    return $r;
}

db_query('SELECT * FROM `userS` WHERE `username` = \''.mysql_real_escape_string($_REQUEST['username']).'\'');