SELECT total_meetings AS meetings,
                               total_attendants AS attendants,
                               round(total_attendants/total_meetings) AS average
                        FROM (
                            (SELECT SUM(attendants) AS total_attendants
                             FROM

                                (SELECT meeting_id AS meeting,
                                       COUNT(member_id) AS attendants
                                 FROM meeting_member
                                 GROUP BY (meeting_id)) AS details) tbl1,

                                (SELECT COUNT(id) AS total_meetings
                                 FROM meetings) tbl2