How many assets does each maintenance contract contain? List the number and the contract id.
SELECT count(*) ,  T1.maintenance_contract_id FROM Maintenance_Contracts AS T1 JOIN Assets AS T2 ON T1.maintenance_contract_id  =  T2.maintenance_contract_id GROUP BY T1.maintenance_contract_id
SELECT count(*) ,  T1.maintenance_contract_id FROM Maintenance_Contracts AS T1 JOIN Assets AS T2 ON T1.maintenance_contract_id  =  T2.maintenance_contract_id GROUP BY T1.maintenance_contract_id
[{'count(*)': 2, 'maintenance_contract_id': 2}, {'count(*)': 2, 'maintenance_contract_id': 6}, {'count(*)': 2, 'maintenance_contract_id': 7}, {'count(*)': 2, 'maintenance_contract_id': 8}, {'count(*)': 1, 'maintenance_contract_id': 10}, {'count(*)': 2, 'maintenance_contract_id': 11}, {'count(*)': 1, 'maintenance_contract_id': 12}, {'count(*)': 1, 'maintenance_contract_id': 13}, {'count(*)': 1, 'maintenance_contract_id': 14}, {'count(*)': 1, 'maintenance_contract_id': 15}]