title: Get the last entry on LEFT JOIN a table
body: <p>I have a query </p>
  
  <pre><code>SELECT cm.posted_at, s.id, s.name, s.device, co.status, co.last_seen, d.device_id 
  FROM station s LEFT JOIN chat_online co 
  ON s.id = co.station_id AND s.device = co.device_id 
  LEFT JOIN device d ON s.device=d.id 
  LEFT JOIN chat_message cm ON cm.station_id=s.id 
  WHERE s.status='1' AND (co.role='station' OR co.role IS NULL) 
  GROUP BY s.id 
  ORDER BY cm.posted_at DESC
  </code></pre>
  
  <p>where in chat_message have multiple entry for one station while executing above query i am getting the first entry of chat_message corresponding to each station_id. How can i retrieve the last entry of chat_message while left joining the chat_message with station</p>
  
  <p>Thank in Advance </p>