// 低版本5.7以下可以生效
SELECT *
FROM  (select * from tabletable where xxx order by update_time DESC) b 
GROUP BY b.user_id;

// 所有版本均适用
SELECT t.*
FROM (
      SELECT user_id, MAX(update_time) as update_time
      FROM tabletable
      WHERE xxx
      GROUP BY user_id
) r
INNER JOIN tabletable t
ON t.user_id = r.user_id AND t.update_time = r.update_time
GROUP BY t.user_id;