SELECT mx.Ticket_Closed_Date, mx.Interval, op.*	 
FROM ( -- create a matrix containing all intervals from Tijdsintervallen and all dates & Event_Channels from Tussen_Tickets
	SELECT * 
	FROM Tijdsintervallen 
	CROSS JOIN (
		SELECT DISTINCT Ticket_Closed_Date = CAST(Ticket_Closed_DateTime AS DATE) 
		FROM Tussen_Tickets
	) d
	CROSS JOIN (
		SELECT DISTINCT Event_Channel
		FROM Tussen_Tickets
	) e
) mx
OUTER APPLY (
	SELECT tt.Event_Channel,
		DVBIntern = SUM(tt.DVBIntern), 
		DVBExtern = SUM(tt.DVBExtern), 
		Tijdsduur = SUM(tt.Tijdsduur), 
		WrapUp = SUM(tt.WrapUp), 
		OnHold = SUM(tt.OnHold), 
		Talk = SUM(tt.Talk),
		RowsAggregated = COUNT(*) -- not in spec but handy to have 
	FROM Tussen_Tickets tt
	CROSS APPLY (
		SELECT 
			Ticket_Closed_Time = CAST(tt.Ticket_Closed_DateTime AS TIME(3)),
			Ticket_Closed_Date = CAST(tt.Ticket_Closed_DateTime AS DATE)
		) ta
	WHERE ta.Ticket_Closed_Time BETWEEN mx.beginTijdsinterval AND mx.eindTijdsinterval
		AND ta.Ticket_Closed_Date = mx.Ticket_Closed_Date
		AND tt.Event_Channel = mx.Event_Channel
	GROUP BY ta.Ticket_Closed_Date, tt.Event_Channel
) op
ORDER BY mx.Ticket_Closed_Date, mx.Interval, op.Event_Channel;

SELECT *
INTO #Matrix 
FROM Tijdsintervallen 
CROSS JOIN (
	SELECT DISTINCT Ticket_Closed_Date = CAST(Ticket_Closed_DateTime AS DATE) 
	FROM Tussen_Tickets
) d
CROSS JOIN (
	SELECT DISTINCT Event_Channel
	FROM Tussen_Tickets
) e

CREATE UNIQUE CLUSTERED INDEX ucx_Everything ON #Matrix (Event_Channel, Ticket_Closed_Date, beginTijdsinterval)
-----------------------------------------------------

SELECT mx.Ticket_Closed_Date, mx.Interval, op.*	 
FROM #Matrix mx
OUTER APPLY (
	SELECT tt.Event_Channel,
		DVBIntern = SUM(tt.DVBIntern), 
		DVBExtern = SUM(tt.DVBExtern), 
		Tijdsduur = SUM(tt.Tijdsduur), 
		WrapUp = SUM(tt.WrapUp), 
		OnHold = SUM(tt.OnHold), 
		Talk = SUM(tt.Talk),
		RowsAggregated = COUNT(*) -- not in spec but handy to have 
	FROM Tussen_Tickets tt
	CROSS APPLY (
		SELECT 
			Ticket_Closed_Time = CAST(tt.Ticket_Closed_DateTime AS TIME(3)),
			Ticket_Closed_Date = CAST(tt.Ticket_Closed_DateTime AS DATE)
		) ta
	WHERE ta.Ticket_Closed_Time BETWEEN mx.beginTijdsinterval AND mx.eindTijdsinterval
		AND ta.Ticket_Closed_Date = mx.Ticket_Closed_Date
		AND tt.Event_Channel = mx.Event_Channel
	GROUP BY ta.Ticket_Closed_Date, tt.Event_Channel
) op
ORDER BY mx.Ticket_Closed_Date, mx.Interval, op.Event_Channel;