How many businesses are there in Scottsdale city under the category of "Beauty & Spas"?
category refers to category_name;
SELECT COUNT(T2.business_id) FROM Categories AS T1 INNER JOIN Business_Categories AS T2 ON T1.category_id = T2.category_id INNER JOIN Business AS T3 ON T2.business_id = T3.business_id WHERE T3.city LIKE 'Scottsdale' AND T1.category_name LIKE 'Beauty & Spas'