unread count and grouping - mysql

Question

I have a very similar setup to this answer Is there a simpler way to achieve this style of user messaging?
However I'm having an issue with getting the total unread conversations and not unread messages.
SELECT p.conversation_id, COUNT(p.conversation_id) as unread
FROM participation AS p
INNER JOIN messages AS m
ON m.conversation_id = p.conversation_id AND m.seen = 0
WHERE p.uid1 = {$user->data['id']}
GROUP BY m.conversation_id`
I'm only selecting p.conversation_id for testing purposes, but the result I am getting is:
Array
(
[conversation_id] => 1
[unread] => 77
)
If I were to put the results in a PHP while loop I get
Array
(
[conversation_id] => 1
[unread] => 77
)
Array
(
[conversation_id] => 3
[unread] => 7
)
Array
(
[conversation_id] => 8
[unread] => 1
)
Array
(
[conversation_id] => 17
[unread] => 35
)
Array
(
[conversation_id] => 22
[unread] => 2
)
Array
(
[conversation_id] => 24
[unread] => 305
)
Array
(
[conversation_id] => 29
[unread] => 41
)
Array
(
[conversation_id] => 31
[unread] => 1
)
The result I am wanting is unread: 8

Answer 1

I think you just want conditional aggregation:
SELECT p.conversation_id,
SUM(m.seen = 0) as unseen,
SUM(m.seen <> 0) as seen
FROM participation AS p INNER JOIN
messages AS m
ON m.conversation_id = p.conversation_id AND m.seen = 0
WHERE p.uid1 = {$user->data['id']}
GROUP BY m.conversation_id
In addition, if you want the total over all conversations, leave out the group by.