Select distinct and count other table - mysql

Question

In a small chat service, two users have a common chat.
This SQL selects a list of the users that you have chatted with.
SELECT DISTINCT user.user_id, user.username
FROM user
INNER JOIN message
ON user.user_id = message.owner_user_id OR user.user_id = message.to_user_id
WHERE message.owner_user_id = :activeUserId
OR message.to_user_id = :activeUserId
ORDER BY message.date_time DESC
I also need to get the number of messages that has been sent between two users. The output is a list of "folders", one for each user, the active user has chatted with. Each folder contains the username of the user and the number of messages in the chat (the sum of the active user's number of messages to the specific user, and the specific user's number of messages to the active user).
row1: (active user and JohnSmith have 33 messsages in their common chat.)
user_id = 1;
username = 'JohnSmith';
message_count = 33;
row2: (active user and Johnny have 43 messsages in their common chat.)
user_id = 2;
username = 'Johnny';
message_count = 43;
How could this be done in one SQL-statement?

Answer 1

Right now you're "flattening" the results using DISTINCT. You can flatten and count using the COUNT(*) function and GROUP BY:
SELECT DISTINCT user.user_id, user.username, COUNT(*)
FROM user
INNER JOIN message
ON user.user_id = message.owner_user_id OR user.user_id = message.to_user_id
WHERE message.owner_user_id = :activeUserId OR message.to_user_id = :activeUserId
GROUP BY user.user_id, user.username
ORDER BY message.date_time DESC
The only changes to your query are the additional column (COUNT(*)) and the GROUP BY line.

Answer 2

Your question seems a bit ambiguous. It seems like you want to count the messages from one user to each other user they communicate with -- regardless of whether they are the "from" or "to" roles on the message.
When dealing with messages, one approach is to normalize them with the smaller user id first and then the larger user id. The result from such a query would be one row for your users, that looks like:
1 'JohnSmith' 2 'Johnny' 33
rather than two separate rows. You can get the two separate rows as well, but that seems less useful to me.
The query that produces that style of output is:
select least(m.owner_user_id, m.to_user_id) as uid1,
greatest(m.owner_user_id, m.to_user_id) as uid2,
u1.username, u2.username, count(*) as nummessages
from message m join
user u1
on u1.user_id = least(m.owner_user_id, m.to_user_id) join
user u2
on u2.user_id = greatest(m.owner_user_id, m.to_user_id)
WHERE m.owner_user_id = :activeUserId or
m.to_user_id = :activeUserId
group by least(m.owner_user_id, m.to_user_id) as uid1,
greatest(m.owner_user_id, m.to_user_id);

Answer 3

Try:
SELECT DISTINCT(user.user_id), user.username, COUNT(c.to_user_id) AS message_count
FROM user
INNER JOIN message
ON user.user_id = message.owner_user_id
OR user.user_id = message.to_user_id
INNER JOIN message m1
ON user.user_id = m1.owner_user_id
OR user.user_id = m1.to_user_id
WHERE message.owner_user_id = :activeUserId
OR message.to_user_id = :activeUserId
ORDER BY message.date_time DESC