Rough calculation of online time, bug:ip the same _php skills

? Php
/*

CREATE TABLE ' Db_online ' (
' IP ' char ' default NULL,
' Time ' char ' is not NULL default ',
' Name ' char ' not NULL default ' visitor '
) Type=myisam

*/

Rough calculation of online time, bug:ip the same (LAN-> external network), only record one person. But the odds are low.

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 obsolete 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 ', ' tourist '));
}

?>