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CREATE TABLE tickets ( id INT, subject VARCHAR(20) );
INSERT INTO tickets VALUES
(1, 'Ticket1'),
(2, 'Ticket2');
CREATE TABLE tickets_contents ( id INT, ticket_id INT, date_time DATETIME );
INSERT INTO tickets_contents VALUES
(1, 1, '2020-05-24 08:30:15'),
(1, 2, '2020-05-25 10:05:15'),
(1, 1, '2020-05-25 12:15:00');
SELECT tt.id AS ticket_id, tt.subject, tt.date_time AS last_update
FROM
(
SELECT t.*, tc.date_time,
RANK() OVER (PARTITION BY tc.ticket_id ORDER BY tc.date_time DESC ) AS rnk
FROM tickets t
JOIN tickets_contents tc
ON tc.ticket_id = t.id
) tt
WHERE rnk = 1
ORDER BY ticket_id;
| ticket_id | subject | last_update |
|---|---|---|
| 1 | Ticket1 | 2020-05-25 12:15:00 |
| 2 | Ticket2 | 2020-05-25 10:05:15 |