Show the number of transactions for different investors.
SELECT investor_id ,  COUNT(*) FROM TRANSACTIONS GROUP BY investor_id
SELECT investor_id ,  COUNT(*) FROM TRANSACTIONS GROUP BY investor_id
[{'investor_id': 2, 'COUNT(*)': 2}, {'investor_id': 3, 'COUNT(*)': 3}, {'investor_id': 6, 'COUNT(*)': 1}, {'investor_id': 7, 'COUNT(*)': 1}, {'investor_id': 8, 'COUNT(*)': 1}, {'investor_id': 14, 'COUNT(*)': 1}, {'investor_id': 17, 'COUNT(*)': 1}, {'investor_id': 18, 'COUNT(*)': 2}, {'investor_id': 19, 'COUNT(*)': 2}, {'investor_id': 20, 'COUNT(*)': 1}]