What is the description and code of the type of service that is performed the most often?
create table services (service_type_code varchar, PRIMARY KEY (service_type_code)); create table ref_service_types (service_type_description varchar, service_type_code varchar, PRIMARY KEY (service_type_description))
select t1.service_type_description, t1.service_type_code from ref_service_types as t1 join services as t2 on t1.service_type_code = t2.service_type_code group by t1.service_type_code order by count(*) desc limit 1