How did vbulletin close the database

[hurricane_sh]

I can't see any db close statement in php files like showthread.php. I wrote my own php file which uses the $db object, does it look right? Thanks!

PHP Code:

require_once('./global.php');

$result = $db->query_first("select .....");
.....
$db->free_result($result);
$db->close();