select last entry for every user multi table example - sql

Question

Given the following tables
table message
id message time_send
14 "first" 2014-02-10 22:16:31
15 "second" 2014-02-14 09:35:20
16 "third" 2014-02-13 09:35:47
17 "fourth" 2014-03-10 22:16:31
18 "fifth" 2014-03-14 09:35:20
19 "sixth" 2014-04-12 09:35:47
20 "seventh" 2014-04-13 09:35:47
21 "eighth" 2014-04-14 09:35:47
table message_owner
id message_id owner_id cp_id
1 14 1 4
2 14 4 1
3 15 12 4
4 15 4 12
5 16 4 1
6 16 1 4
7 17 12 4
8 17 4 12
9 18 4 1
10 18 1 4
11 19 12 4
12 19 4 12
13 20 12 1
14 20 1 12
15 21 12 7
16 21 7 12
I want to query the most recent message with every counter party(cp_id) for a given owner.
For example for owner_id=4 I would like the following output:
id message time_send owner_id cp_id
18 "fifth" 2014-03-14 09:35:20 4 1
19 "sixth" 2014-02-13 09:35:47 4 12
I see a lot of examples with one table but I am not able to transpose them in a multitable example.
edit1: adding more entries

Answer 1

This should work:
SELECT m.id, m.message, mo.owner_id, mo.cp_id
FROM message m
JOIN message_owner mo ON m.id=mo.message_id
WHERE mo.owner_id=4
AND m.time_send=(
SELECT MAX(time_send)
FROM message m2
JOIN message_owner mo2 ON mo2.message_id=m2.id
WHERE mo2.owner_id=mo.owner_id
AND mo2.cp_id =mo.cp_id
)
... notice though that putting a WHERE condition on a timestamp column can sometimes not work correctly.
Same example without jointures:
SELECT m.id, m.time_send, m.message, mo.owner_id, mo.cp_id
FROM message m, message_owner mo
WHERE m.id = mo.message_id
AND mo.owner_id = 4
AND m.time_send = (
SELECT MAX(time_send)
FROM message m2, message_owner mo2
WHERE mo2.message_id = m2.id
AND mo2.owner_id = mo.owner_id
AND mo2.cp_id = mo.cp_id
);
http://sqlfiddle.com/#!2/558d7/4