Is there a simpler way to achieve this style of user messaging?

Question

I have created a messaging system for users, it allows them to send a message to another user. If it is the first time they have spoken then a new conversation is initiated,

Answer 1

I think you do not need to create a userconversation table.

If only user can have only one conversation with someone, the unique id for this thread is a concat between userId and friendId. So I move the friendId column in usersmessage table. The problem of order (friendId-userId is the same thread of userId-friendId) can be solved so:

SELECT CONCAT(GREATEST(userId,FriendId),"_",LEAST(userId,FriendId)) AS threadId

Now there is a problem of fetch the last message after a GROUP BY threadId.

I think is a good solution make a concat between DATE and message and after a MAX on this field.

I assume, for simplicity, column date is a DATETIME field ('YYYY-mm-dd H:i:s') but it not need because there is FROM_UNIXTIME function.

So the final query is

SELECT 
        CONCAT(GREATEST(userId,FriendId),"_",LEAST(userId,FriendId)) AS threadId,
        friendId, MAX(date) AS last_date, 
        MAX(CONCAT(date,"|",message)) AS last_date_and_message 

FROM usermessages
WHERE userId = :userId OR friendId = :userId
GROUP BY threadId ORDER BY last_date DESC

the result of field last_date_and_message is something like so:

2012-05-18 00:18:54|Hi my friend this is my last message

it can be simply parsed from your server side code.