MySQL Select-将COUNT与GROUP_CONCAT结合

Question

I currently have a MySQL SELECT statement that pulls information from two tables to display a "Sent Messages" field for private messaging.

I'd like to know how I can do add a COUNT to my query to count the number of "receivers" in one thread.

Here's the basic gist of my table structure, (NOTE: the relational tie between the two tables is the 'message-id' in pm-info and the "id" in pm_data):

pm_info:
   id     message_id    receiver_id    is_read     read_date

pm_data:
   id    date_sent    title    sender_id    thread_id    content

Here's my SELECT Statement:

SELECT pm_info.is_read, group_concat(DISTINCT receiver.usrFirst) as receiver_name,
pm_data.date_sent, pm_data.title, pm_data.thread_id, pm_data.id as data_id,
MAX(date_sent) AS thread_max_date_sent
FROM pm_info
INNER JOIN pm_data ON pm_info.message_id = pm_data.id
INNER JOIN tblUsers AS receiver ON pm_info.receiver_id = receiver.usrID
WHERE pm_data.sender_id = '$usrID'
GROUP BY pm_data.thread_id
ORDER BY thread_max_date_sent DESC

And it ouputs the recipients like this:

Message 1 - Recipients: John, David, Steve - thread_id = 1234
Message 2 - Recipients: Bill, David, John, Ed, Steve - thread_id = 1345

Basically, what I'd like to do is have the option to COUNT the recipients, so in the example above, "Message 1" would display three (3) recipients, and "Message 2" would display five (5) recipients.

This way, if I have a thread/message that was sent to 30 users, not all thirty names will be printed out.

Thanks!

Answer 1

Have you tried just replacing GROUP_CONCAT with COUNT? Like this:

COUNT(DISTINCT receiver.usrFirst) as receiver_count

Or better, use pm_info.receiver_id as in (which could potentially let you eliminate one of your joins):

COUNT(DISTINCT pm_info.receiver_id) as receiver_count

Answer 2

You could use a subquery to select up to 3 recipients per message, and then another subquery to concatenate their names:

select 
    (   select group_concat(usrFirst separator ', ') 
        from tblUsers
        where usrId in (
            select usrId
            from tblUsers
            where usrId = pm_info.receiver_id
            limit 3
        )
    ) as receiver_name
 from pm_info
 ....

Answer 3

You could move the count and group_concat into a concat statement.

... group_concat(DISTINCT receiver.usrFirst) as receiver_name ...

becomes

... concat('messages:', count(distinct receiver.usrFirst),'(',group_concat(DISTINCT receiver.usrFirst),')') as receiver_name ...