php สอบถามวิธีการเขียนประยุกต์ใช้โค๊ด user online ค่ะ

$username=$result_show['username'];
$password=$result_show['password'];
session_register("username");
session_register("password");
		
		insert_data("insert into member_login set 
		username='".$_POST['user']."',
		ip='".$_SERVER["REMOTE_ADDR"]."',
		session='".session_id()."',
		datetime='".$datetime."'");

$session=session_id();
$session_db = mysql_query("select count(*) from member_login where session='$session'");
$session_check = mysql_result($session_db,0);
	if($session_check == "0") {
			echo "fff";
			echo "<script language=Javascript>window.location.href=\"../index.php?view=home\";</script>";	
	}else{ 
			                    	unset($_SESSION["username"]); // ลบบาง Session
				                    unset($_SESSION["password"]); // ลบบาง Session
				                    session_destroy(); // ลบ Session ทั้งหมด
			
			echo "<script language=Javascript>window.location.href=\"../index.php?view=home\";</script>";	
	}