Custom code for Online user not wroks perfectly

Hello guys,

I am making a classified website with classipress,

https://www.mohibsalahuddin.com/client/ads/test-ad/

for showing author is online or offline on ad page, i wirte the following code, but it doesnot work if two users registered at a time..if registered user want to see another registered user status it shows offline always.. I write the code below

First I create the table in MYSQL
CREATE TABLEwordpress_users_online` (
user_id int(11) default NULL,
full_name varchar(64) NOT NULL default ”,
session_id varchar(128) NOT NULL default ”,
ip_address varchar(15) NOT NULL default ”,
time_entry varchar(14) NOT NULL default ”,
time_last_click varchar(14) NOT NULL default ”,
last_page_url varchar(255) NOT NULL default ”
) ENGINE=MyISAM;`

THEN I WRITE THE FILE wordpress_users_online.php with following code

[Code moderated as per the Forum Rules. Please use the pastebin]