how to only rotate in y axis in unity code example

Example 1: unity rotate around axis

transform.Rotate(axis, degrees);

Example 2: look rotation only on y axis in unity

Vector3 relativePos = target.position - transform.position;          Quaternion LookAtRotation = Quaternion.LookRotation( relativePos );            Quaternion LookAtRotationOnly_Y = Quaternion.Euler(transform.rotation.eulerAngles.x, LookAtRotation.eulerAngles.y, transform.rotation.eulerAngles.z);            transform.rotation = LookAtRotationOnly_Y;