Question

I have two tables.

One of them called “conversations” has the following data.

ConversationID  Sender     Reciever
1               bla1       bla2
2               bla1       bla3
3               bla1       bla4

The other is called “Messages” has the following data.

MessageID    MessageText    TimeAddedMessage        ConversationID
1             helo           2012-03-12 13:00:00          2
2             helo           2012-03-12 13:01:00          1
3             helo           2012-03-12 13:02:00          3
4             helo           2012-03-12 13:03:00          3
5             helo           2012-03-12 13:04:00          2

The result i want from the query is the following:

5             helo           2012-03-12 13:04:00          2
4             helo           2012-03-12 13:03:00          3
2             helo           2012-03-12 13:01:00          1

Which means that we need the most recent comment for each conversation (sorted DESC by time).

Any help appreciated.

Answer 1

Try –

SELECT m2.*, c.Sender
FROM (
    SELECT m1.ConversationID, MAX(m1.MessageID) AS MessageID
    FROM Messages m1
    GROUP BY m1.ConversationID
) latest_msg
INNER JOIN Messages m2
    ON latest_msg.MessageID = m2.MessageID
    AND latest_msg.ConversationID = m2.ConversationID
INNER JOIN Conversations c
    ON m2.ConversationID = c.ConversationID
ORDER BY m2.MessageID DESC

EDIT I have modified the above query to include the value of Sender from the Conversations table. I have noticed that your structure for the conversation is a bit odd. A conversation is FROM one user TO another user but there is no way to identify which user wrote each message. Is this intentional?