What subquery do I need to calculate this report?
I've got this far (DDL and DML below)

SELECT ticket_id, c_max_date FROM
( 
  SELECT ticket_id, MAX(FROM_UNIXTIME(comment.comments_timestamp)) AS c_max_date
  FROM comment
  WHERE comment.comments_timestamp &lt; UNIX_TIMESTAMP(NOW() - INTERVAL 2 YEAR)
  GROUP BY ticket_id
) AS mytab;

+-----------+---------------------+
| ticket_id | c_max_date          |
+-----------+---------------------+
|         3 | 2004-07-09 15:15:30 |
|         4 | 2006-06-30 15:15:30 |
+-----------+---------------------+


These two comments are indeed the ticket number of tickets whose comments haven't been updated in 2 years (arbitrary choice). The dates are the dates of the last update to the ticket comments.

Can you (anyone) put the finishing touch to this and join mytab to tickets? My brain is fried!

CREATE TABLE IF NOT EXISTS ticket
(
  ticket_id INT NOT NULL,
  ticket_description TEXT NULL,
  PRIMARY KEY (ticket_id)
);



CREATE TABLE IF NOT EXISTS comment 
(
  comment_id INT NOT NULL,
  ticket_id INT NOT NULL,
  comments_comment VARCHAR(45) NULL,
  comments_timestamp INT NULL,
  PRIMARY KEY (comment_id),
  INDEX ticket_index (ticket_id),
  FOREIGN KEY (ticket_id) REFERENCES ticket (ticket_id)
);


INSERT INTO ticket VALUES(1, 'ticket 1');
INSERT INTO ticket VALUES(2, 'ticket 2');
INSERT INTO ticket VALUES(3, 'ticket 3');
INSERT INTO ticket VALUES(4, 'ticket 4');
INSERT INTO ticket VALUES(5, 'ticket 5');

INSERT INTO comment VALUES(1, 1, 'comment 1 on ticket 1', UNIX_TIMESTAMP('2013-11-30 15:15:30'));
INSERT INTO comment VALUES(2, 1, 'comment 2 on ticket 1', UNIX_TIMESTAMP('2014-02-13 15:15:30'));
INSERT INTO comment VALUES(3, 1, 'comment 3 on ticket 1', UNIX_TIMESTAMP('2014-06-30 15:15:30'));
INSERT INTO comment VALUES(4, 1, 'comment 4 on ticket 1', UNIX_TIMESTAMP('2014-07-09 15:15:30'));
INSERT INTO comment VALUES(5, 2, 'comment 1 on ticket 2', UNIX_TIMESTAMP('2013-11-30 15:15:30'));
INSERT INTO comment VALUES(6, 2, 'comment 2 on ticket 2', UNIX_TIMESTAMP('2014-02-13 15:15:30'));
INSERT INTO comment VALUES(7, 2, 'comment 3 on ticket 2', UNIX_TIMESTAMP('2014-07-30 15:15:30'));
INSERT INTO comment VALUES(8, 2, 'comment 4 on ticket 2', UNIX_TIMESTAMP('2014-08-09 15:15:30'));
INSERT INTO comment VALUES(9, 3, 'comment 1 on ticket 3', UNIX_TIMESTAMP('2003-11-30 15:15:30'));
INSERT INTO comment VALUES(10, 3, 'comment 2 on ticket 3', UNIX_TIMESTAMP('2002-02-13 15:15:30'));
INSERT INTO comment VALUES(11, 3, 'comment 3 on ticket 3', UNIX_TIMESTAMP('2004-06-30 15:15:30'));
INSERT INTO comment VALUES(12, 3, 'comment 4 on ticket 3', UNIX_TIMESTAMP('2004-07-09 15:15:30'));
INSERT INTO comment VALUES(13, 4, 'comment 1 on ticket 4', UNIX_TIMESTAMP('2003-11-30 15:15:30'));
INSERT INTO comment VALUES(14, 4, 'comment 2 on ticket 4', UNIX_TIMESTAMP('2004-02-13 15:15:30'));
INSERT INTO comment VALUES(15, 4, 'comment 3 on ticket 4', UNIX_TIMESTAMP('2006-06-30 15:15:30'));
INSERT INTO comment VALUES(16, 4, 'comment 4 on ticket 4', UNIX_TIMESTAMP('2004-07-09 15:15:30'));
INSERT INTO comment VALUES(17, 5, 'comment 1 on ticket 1', UNIX_TIMESTAMP('2013-11-30 15:15:30'));
INSERT INTO comment VALUES(18, 5, 'comment 2 on ticket 2', UNIX_TIMESTAMP('2014-02-13 15:15:30'));
INSERT INTO comment VALUES(19, 5, 'comment 3 on ticket 3', UNIX_TIMESTAMP('2014-06-30 15:15:30'));
INSERT INTO comment VALUES(20, 5, 'comment 4 on ticket 4', UNIX_TIMESTAMP('2014-07-09 15:15:30'));