query sum two Different table : [enter image description here][1]


  [1]: https://i.stack.imgur.com/bZDlo.jpg
i have two different 
					
		ork3		ork2	
	k3	k1		k11	k1
	1	a		2	a
	4	b		3	b
	5	c		4	c
	3	a		7	a
				3	a
				1	b
					
					
					
					
					
		k1    sum(k3)  sum(k11)   (sumk3-sumk11)
        a       11          4        7
        b        4          4         0
        c        4          5         -1

i want value null in sum(sumk3-sumk11) not appear in query 
