MySQL Weekdag/Weekend tellen - Deel II

SELECT 
  fname, 
  MONTH(eventDate), 
  SUM(IF(WEEKDAY(eventDate) < 5,1,0)) AS WeekdayCount,
  SUM(IF(WEEKDAY(eventDate) >= 5,1,0)) AS WeekendCount
FROM eventcal AS e
LEFT JOIN users AS u ON e.primary = u.username
GROUP BY fname, MONTH(eventDate);

U wilt uw aggregaties (in dit geval SUM) doen in de SELECT en GROUP BY hoe u ze wilt optellen (op fname, op MAAND).