интересно же посмотреть, как оно работает!

SELECT
	Review.id, Review.name, Review.parent_id, COUNT(DoctorReview.user_id)
FROM
	reviews AS Review
	LEFT JOIN doctor_reviews AS DoctorReview ON DoctorReview.option_id = Review.id AND DoctorReview.doctor_id = $doctor
WHERE
	Review.review_id = 1
GROUP BY
	Review.id