Question

I’m trying to group messages in conversations, so they can be read as a conversation.

This is what I have right now

Table messages

id | from | to | message | timestamp  
1  | 1    | 2  | 'Hello' | 1351257766
2  | 1    | 3  | 'Hey!'  | 1351257767
3  | 2    | 1  | 'Hay!'  | 1351257768

Whereas the messages.from and messages.to fields correspond to a row in the users table.

What I want to do is: (not in the same query)

a. Get a list of the last messages of all the conversations from a user (so where either from or to is equal to a given user.id
b. Get all the messages that belong to a conversation.

SELECT
-- From-user:
    users_from.id               AS from_id,
    users_from.username         AS from_username,
    users_from.nickname         AS from_nickname,
    users_from.username_safe    AS from_username_safe,
    users_from.password         AS from_password,
    users_from.email            AS from_email,
    users_from.rank             AS from_rank,
    users_from.email            AS from_email,
    users_from.ip               AS from_ip,
    users_from.last_online      AS from_last_online,
    users_from.register_stamp   AS from_register_stamp,
    users_from.state            AS from_state,
    users_from.icon             AS from_icon,

-- To-user:
    users_to.id                 AS to_id,
    users_to.username           AS to_username,
    users_to.nickname           AS to_nickname,
    users_to.username_safe      AS to_username_safe,
    users_to.password           AS to_password,
    users_to.email              AS to_email,
    users_to.rank               AS to_rank,
    users_to.email              AS to_email,
    users_to.ip                 AS to_ip,
    users_to.last_online        AS to_last_online,
    users_to.register_stamp     AS to_register_stamp,
    users_to.state              AS to_state,
    users_to.icon               AS to_icon,

-- Messages:
    messages.id,
    messages.from,
    messages.to,
    messages.message,
    messages.timestamp


FROM messages

-- Some joins to get the userdata
INNER JOIN users AS users_to
    ON messages.to = users_to.id
INNER JOIN users AS users_from
    ON messages.from = users_from.id

-- We only want the latest messages:
RIGHT JOIN (
    SELECT
        max(messages.id) AS maxid,
        messages.from,
        messages.to
    FROM messages
    WHERE messages.to = {userid} OR messages.from = {userid}
) limiter
    ON messages.id = limiter.maxid

This is what I am using right now, but it isn’t working. It returns only one of the conversations.

I hope you guys can help me make this work!

UPDATE:
The answer that was given did not work. When user-1 sent a message to user-2, it worked. However when user-2 replied, it began a separate conversation (as a new row in the result).

Answer 1

Your query is close, but I think you need to group by the users as well. This is one approach

RIGHT JOIN (
    SELECT
        max(messages.id) AS maxid,
        messages.from,
        messages.to
    FROM messages
    WHERE messages.to = {userid} OR messages.from = {userid}
    group by messages.from, messages.to
) limiter

Your definition of conversation appears to be having the same two users. For this, use in:

select m.*
from messages m
where `from` in ({userid1}, {userid2}) and
      `to` in ({userid1}, {userid2})

By the way, from and to are bad column names, because from is a reserved word.