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', 'rvcr4t9lcrlnkhpbvgtf5cjeq0', '216.73.216.171', '1751429471', '1751429471', '/xtshop/product_info.php?info=p1086_.html')

[XT SQL Error]