psql -h $POSTGRES_HOST -U $POSTGRES_USER $POSTGRES_DB
\du  # list all users
\l  # list databases
\c  # select a database
\d  # list tables
\d+ <table_name>  # describe table
\dx  # list installed extensions
SELECT * FROM pg_available_extensions;  # list extensions available on the server
CREATE EXTENSION IF NOT EXISTS <ext_name>;  # install an extension
ALTER EXTENSION <ext_name> UPDATE TO 'new_version';  # upgrade an extension