I want to find the equation of the intersection between a sphere and cylinder (in the first octant) but it's kind of weird.

Sphere: x^2 + y^2 +z^2 = 4

Cylinder: x^2 + y^2 - 2y = 0

If I just sub one of them into the other I get:

2y + z^2 = 4

but that doesn't make sense to me since that is an equation of a surface since x can vary. There should be some sort of restriction on x... but how do I get this?