How many type codes are there?
select count(distinct apt_type_code) from apartments
For each type code, show how many apartments.
select apt_type_code, count(*) from apartments group by apt_type_code
What are the apartment numbers of the apartments with type code "Studio"?
select apt_number from apartments where apt_type_code = "Studio"
What about type code "Flat"?
select apt_number from apartments where apt_type_code = "Flat"