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', 'a1e1ec97a4a88636f7e44b96b019c9d6', '216.73.216.42', '1763354821', '1763354821', '/shop/product_info.php?info=p31_.html')

[XT SQL Error]