Rough calculation of online time, bug: same IP_PHP tutorial

/*

CREATE TABLE `db_online` (
`ip` char(20) default NULL,
`time` char(20) NOT NULL default '',
`name` char(200) NOT NULL default 'Guest'
) TYPE=MyISAM

*/

//Rough calculation of online time, bug: same IP (LAN ->external network), only one person is recorded. But the chance is very small

session_start();
//Timeout time
$out_time=300;//60*5

$uesr_name=$_SESSION['uesr_name'] ;

$now=time();
$online="db_online";
$ip=$_SERVER["REMOTE_ADDR"];

mysql_connect("localhost", "root","");
mysql_select_db("database");
//Delete outdated users.
mysql_query("delete from `$online` where ($now-`time`)> $out_time or `name`='$uesr_name' or `ip`='$ip' ");

if($uesr_name){
mysql_query(" INSERT INTO `$online` (`ip `, `time`, `name`) VALUES ('$ip','$now','$uesr_name') ");
}else{
mysql_query(" INSERT INTO `$online` (` ip`, `time`, `name`) VALUES ('$ip','$now','visitor') ");
}

?>