Among the businesses with average rating, how many business has attribute of full_bar.
average rating refers to avg(stars); attribute of full_bar refers to attribute_value = 'full_bar'
SELECT COUNT(T1.business_id) FROM Business_Attributes AS T1 INNER JOIN Business AS T2 ON T1.business_id = T2.business_id WHERE T1.attribute_value = 'full_bar'