CREATE TABLE student (stuid DECIMAL, lname TEXT, fname TEXT, age DECIMAL, sex TEXT, major DECIMAL, advisor DECIMAL, city_code TEXT)
CREATE TABLE dorm (dormid DECIMAL, dorm_name TEXT, student_capacity DECIMAL, gender TEXT)
CREATE TABLE lives_in (stuid DECIMAL, dormid DECIMAL, room_number DECIMAL)
CREATE TABLE has_amenity (dormid DECIMAL, amenid DECIMAL)
CREATE TABLE dorm_amenity (amenid DECIMAL, amenity_name TEXT)

Find the average age of all students living in the each city.
SELECT AVG(age), city_code FROM student GROUP BY city_code
SELECT AVG("age"), "city_code" FROM "student" GROUP BY "city_code"