How to check whether the postgres_fdw extension is installed in postgres

Question

I need to use postgres_fdw to link two database. According to this guide, the first step is to install postgres_fdw extension.

How can I check this is already installed on the server or not?

Answer 1

I think I fond how to check it:

select * from pg_extension where extname='postgres_fdw';

pg_extension seems to have the list of installed extensions.