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);
Du vil lave dine aggregeringer (SUM i dette tilfælde) i SELECT, og GRUPPER EFTER, hvordan du vil have dem samlet (efter fnavn, efter MÅNED).