$query = $db->query("SELECT * FROM {$tablepre}threads t WHERE tid='$tid' AND displayorder>='0'");
$var = $db->fetch_array($query);

function query_cache($sql,$ttl=86400) {
        if ($sql == '')
                return null;

        global $db;
        $iKey = md5($sql);
        if (!$cached_res = apc_fetch($iKey)) {
                $query = $db->query($sql);
                while($this_res = $db->fetch_array($query)) {
                        $cached_res[]        =        $this_res;
                }
                apc_store($iKey, $cached_res,$ttl);
        return $cached_res;
}

$sql = "SELECT * FROM {$tablepre}threads t WHERE tid='$tid' AND displayorder>='0'"
$var = query_cache($sql);