Calculate the average rating of reviews for restaurants in Santa Cruz County.
average rating = divide(sum(review where county = 'santa cruz county'), count(id_restaurant where county = 'santa cruz county'))
SELECT AVG(T2.review) FROM geographic AS T1 INNER JOIN generalinfo AS T2 ON T1.city = T2.city WHERE T1.county = 'santa cruz county'
database name:db_id restaurant
geographic table geographic Cols: city dtype text, country dtype text, region dtype text, 
generalinfo table generalinfo Cols: id restaurant dtype integer, label dtype text, food type dtype text, city dtype text, review dtype real, 
location table location Cols: id restaurant dtype integer, street number dtype integer, street name dtype text, city dtype text, 
