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', '9sj5upsegkk7vg8j0reev2f923', '216.73.216.165', '1752311541', '1752311541', '/index.php?XTCsid=6bac086b61c18464b20a5897fc76826b')

[XT SQL Error]