How many assets does each maintenance contract contain? List the number and the contract id.
CREATE TABLE Assets (maintenance_contract_id VARCHAR); CREATE TABLE Maintenance_Contracts (maintenance_contract_id VARCHAR)
[SQL] 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 [/SQL]