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', '3hn23q5jusdeqgqvc98q5gp1v1', '216.73.216.110', '1752046784', '1752046784', '/index.php?language=de&XTCsid=adc8c520bddaa9e02a40df1e2a90f128')

[XT SQL Error]