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', 't6cjo7r2eclgu30pacttv73mu5', '216.73.216.139', '1765897971', '1765897971', '/xtshop/product_info.php?info=p429_.html')

[XT SQL Error]