Database: assets_maintenance
Question: Which third party companies have at least 2 maintenance engineers or have at least 2 maintenance contracts? List the company id .
SQL: select t1.company_id from third_party_companies as t1 join maintenance_engineers as t2 on t1.company_id  =  t2.company_id group by t1.company_id having count(*)  >=  2 union select t3.company_id from third_party_companies as t3 join maintenance_contracts as t4 on t3.company_id  =  t4.maintenance_contract_company_id group by t3.company_id having count(*)  >=  2