z=2-Sqrt[-2 x^2-2 x y+2 x-y^2+2 y]

z=Sqrt[-2 x^2-2 x y+2 x-y^2+2 y]+2

Drawing with Mathematica:

contourplot 3d[2 x^2+y^2+z^2+2 x y-2 x-2y-4 z+4 = = 0，{x，- 1， 1}，{y，- 1，2}，{z， 1，3}]