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', 't13tlrj7ob3hkndvum2iin77d7', '216.73.216.209', '1766031998', '1766031998', '/xtshop/product_info.php?info=p394_.html')

[XT SQL Error]