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', 'm1e5mll90rqub6dan1udeompe1', '216.73.217.92', '1781008278', '1781008278', '/xtshop/index.php?cat=c44_.html')

[XT SQL Error]