Show all cities and corresponding number of students.
SELECT city_code ,  count(*) FROM Student GROUP BY city_code
SELECT city_code ,  count(*) FROM Student GROUP BY city_code
[{'city_code': 'ATL', 'count(*)': 1}, {'city_code': 'BAL', 'count(*)': 4}, {'city_code': 'BOS', 'count(*)': 1}, {'city_code': 'CHI', 'count(*)': 1}, {'city_code': 'DAL', 'count(*)': 1}, {'city_code': 'DET', 'count(*)': 1}, {'city_code': 'HKG', 'count(*)': 3}, {'city_code': 'HOU', 'count(*)': 1}, {'city_code': 'LON', 'count(*)': 1}, {'city_code': 'LOS', 'count(*)': 1}, {'city_code': 'NAR', 'count(*)': 1}, {'city_code': 'NYC', 'count(*)': 3}, {'city_code': 'PEK', 'count(*)': 1}, {'city_code': 'PHL', 'count(*)': 3}, {'city_code': 'PIT', 'count(*)': 4}, {'city_code': 'ROC', 'count(*)': 1}, {'city_code': 'SFO', 'count(*)': 1}, {'city_code': 'WAS', 'count(*)': 3}, {'city_code': 'YYZ', 'count(*)': 2}]