CREATE PROCEDURE update_time(IN input_user_id INT )
BEGIN
  DECLARE seconds_since_last           INT;

  START TRANSACTION;
  SELECT TIMESTAMPDIFF(SECOND, lasttime, NOW()) INTO seconds_since_last
    FROM user
    WHERE user_id = input_user_id
    FOR UPDATE
    ;
  UPDATE user
    SET lasttime = NOW()
    WHERE user_id = input_user_id
    ;

  SELECT seconds_since_last;

  COMMIT;
END