How to limit dropdown list to options based on 'in use' rows from lookup table, for webpage using php and postgresql

I have a table country with a lookup table to country_type.

table country

country_id (pk), col2, col3, country_type_id (fk) integer

lookup table

country_type country_type_id (pk), type_name varchar

My lookup table has 50 country types, but only 20 are 'in use' in the
current db (with the rest possibly used later as the db expands). On the
webpage I am creating (I am using a php generator) I can set it up to add a
filter by country type based on the country type_name varchar - so one can
view the country types by name rather than the id integer - but all 50
types are listed.

I only want the 20 that currently 'in use' (not sure if this is the best
way to describe it) and therefore relevant to searches/filters (i.e. I
don't want to see a "There are no records to display" message).

What WHERE condition can I use to achieve this?

Killian Driscoll