query: SELECT avg(age) ,  city_code FROM student GROUP BY city_code
question: Find the average age of all students living in the each city.
query_toks: SELECT avg ( age ) , city_code FROM student GROUP BY city_code
query_toks_no_value: select avg ( age ) , city_code from student group by city_code
question_toks: Find the average age of all students living in the each city.