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', '7gud1vlq1jb8t5btuoqph6vhe0', '216.73.216.147', '1751585667', '1751585667', '/product_info.php?language=de&info=p16_Octoberfest-CD.html&XTCsid=d6a8bfd6f6ba5ba5c5448fc18660454f')

[XT SQL Error]