No me lo acepta en esa posición.
Código:
SELECT u.*, GROUP_CONCAT (j.`idjob`) AS idjob
FROM `users` u
LEFT JOIN `jobs` j ON (j.`userid` = u.`iduser`)
WHERE u.`active` = 1 AND u.`usertypeid`=6
GROUP BY u.`iduser`;
#1305 - FUNCTION mydb.GROUP_CONCAT does not exist