Select Zn, sum(Q1)as Col1, sum(Q2)as Col2, sum(Q3)as Col3
From (SELECT     n1 As Zn, COUNT(n1) AS Q1, 0  as Q2,  0  as Q3
	FROM     TbTst
	WHERE    not(n1 is null)
	GROUP BY n1
	union
	SELECT    n2 As Zn,  0  as Q1,COUNT(n2) AS Q2,  0  as Q3
	FROM         TbTst
	WHERE    not(n2 is null)
	GROUP BY n2
	UNION
	SELECT    n3 As Zn,  0  as Q1,  0  as Q2,COUNT(n3) AS Q3
	FROM         TbTst
	WHERE    not(n3 is null)
	GROUP BY n3) as t1
GROUP BY t1.Zn