SELECT user_name, rev_timestamp AS 'Last edit', GROUP_CONCAT(ug1.ug_group) AS 'user_groups'

FROM `user`

LEFT JOIN user_groups ug1

    ON user_id = ug1.ug_user AND ug1.ug_group IN ('reviewer', 'sysop', 'bot')

JOIN `actor`

    ON actor_user = user_id

JOIN `revision_userindex`

    ON rev_id = (SELECT rev_id FROM revision_userindex

                 WHERE actor_id = rev_actor

                 ORDER BY rev_timestamp DESC

                 LIMIT 1)

WHERE rev_timestamp > (DATE_FORMAT((NOW() - INTERVAL 31 DAY),'%Y%m%d%H%i%S'))

    AND ug1.ug_group IS NOT NULL

GROUP BY user_name

ORDER BY rev_timestamp

;