Getting X results from SQL with multiple tables - mysql

Question

(Sorry for my bad english, I'll try to be the clearest)
I want to select 5 conversations (over an undetermined number, there could be 5 or 300 conversations) of one user in a MySQL table, and for each of those, I want to select all the users who talk in it.
In a wonderfull world, I'd like to do it with one query.
My query looks like (tables are in french, plz don't hurt me) :
SELECT mc.mc_id, mc.mc_sujet, mc.mc_statut,
miu.mi_ustatut as uself_statut, miu.mi_datelecture as uself_datelecture,
mi.mi_uid, mi.mi_ustatut, mi.mi_datelecture,
u.u_pseudonyme
FROM msg_individus as miu
LEFT JOIN msg_conversations as mc ON mc.mc_id = miu.mi_mcid
LEFT JOIN msg_individus as mi ON mi.mi_mcid = mc.mc_id
LEFT JOIN u_individus as u ON u.u_id = mi.mi_uid
WHERE miu.mi_uid = :u_id
Where msg_individus is the table with participants of a conversation,
msg_conversations is the table of the conversation (id, subject, status),
u_individus is the table with users' informations.
To select only 5 of those conversations, I added something like
GROUP BY mc.mc_id,
LIMIT 0,5
But of course, only one user per conversation is given is this way.
I also tried to write GROUP BY mc.mc_id, mi.mi_uid but this, like no writting a GROUP BY condition, returns 5 iterations like :
(Conversation 1 has two users, conversation 2 has one, conversation 3 has four)
Iteration 1 : conversation 1, user 1
Iteration 2 : conversation 1, user 2
Iteration 3 : conversation 2, user 1
Iteration 4 : conversation 3, user 1
Iteration 5 : conversation 3, user 2
What I want is to get five CONVERSATIONS with all their datas (whatever the number of users in it, etc)
I guess I'll have to use two queries (after getting the 5 conversations, I'll get the users per conversations), but maybe you guys can light me with your knowledges.
Thx.

Answer 1

Use a subquery to get five conversations. I also suggest that you replace the outer joins with inner joins. I think the table keys should all have matches:
SELECT mc.mc_id, mc.mc_sujet, mc.mc_statut,
miu.mi_ustatut as uself_statut, miu.mi_datelecture as uself_datelecture,
mi.mi_uid, mi.mi_ustatut, mi.mi_datelecture,
u.u_pseudonyme
FROM (SELECT miu.*, mc.*
FROM msg_individus miu JOIN
msg_conversations mc
ON mc.mc_id = miu.mi_mcid
WHERE miu.mi_uid = :u_id
ORDER BY rand() -- not necessary, but why not?
LIMIT 5
) ic
msg_individus mi
ON mi.mi_mcid = ic.mc_id JOIN
u_individus u
ON u.u_id = ic.mi_uid;