CB Query Field pulls values from the database. It's not designed to insert anything. It just does a select query then outputs the results as a field. Please see my previous reply as I've already provided you a working example. Another example as follows based off the query you supplied.
Code:
SELECT c.`category`
FROM `#__jblance_user` AS u
LEFT JOIN `#__jblance_category` AS c
ON c.`id` = u.`id_category`
WHERE u.`user_id` = '[user_id]'
Please note the above is provided as is based off your example. It has in no way been tested. Please be sure to test and adjust as needed.