In which streets of the city of San Francisco are there restaurants that serve seafood?
street refers to street_name; seafood refers to food_type = 'seafood'
SELECT T1.street_name FROM location AS T1 INNER JOIN generalinfo AS T2 ON T1.id_restaurant = T2.id_restaurant WHERE T1.city = 'san francisco' AND T2.food_type = 'seafood' AND street_name IS NOT NULL