Question

I have a query like:

SELECT _threads.*, _messages.*
FROM _threads
LEFT JOIN _messages
ON _threads.thread_id = _messages.message_thread_id
WHERE _threads.thread_servicer_id = 'jG5s2b6TRs'
GROUP BY _threads.thread_customer_id

Which returns something like:

How can i modify the query to be able to group by thread_customer_id THEN order by message_time and only pick the row with the latest message_time.

Answer 1

Prequery the threads/messages grouped by customer and get the max posting time per your servicer ID filter. From that, it will return a single customer/datetime. THEN, back-join it back to the messages table AGAIN, but only for the matched date/time, then to the thread that matches your servicer ID.. just in case the slim chance of exact same date/time posting of multiple messages under different servers

SELECT 
      T2.*, 
      M2.*
   FROM
      ( select T.thread_Customer_id,
               MAX( M.Message_Time ) as LatestPost
           from
              _Threads T
                 JOIN _Messages M
                    ON T.Thread_ID = M.Message_Thread_ID
           where
              T.thread_servicer_id = 'jG5s2b6TRs'
           GROUP BY 
              T.thread_customer_id ) PreMax

      JOIN _Messages M2
         on PreMax.LatestPost = M2.Message_Time

         JOIN _Threads T2
            on M2.Message_Thread_ID = T2.Thread_ID
           AND T2.Thread_Customer_ID = PreMax.Thread_Customer_ID
           AND T2.Thread_Servicer_ID = 'jG5s2b6TRs'

   ORDER BY 
      M2.Message_Time DESC