1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, session_id, ip_address, time_entry, time_last_click, last_page_url) values ('', 'Guest', '6bnr9db7u882r3dca2hdodrfs6', '216.73.216.244', '1752203318', '1752203318', '/index.php?language=de&XTCsid=e65207aee44f142683bacdd3544c84a8')

[XT SQL Error]