Cool! As we just learned, there are a few ways of calling a function:

• Using a SELECT statement. You can use a regular SELECT in SQL (not in PL/pgSQL):

  SELECT add_topic('Quick cakes');

• In PL/pgSQL, you can:
  • Use the SELECT INTO syntax to save a query result:

    SELECT thumbs_up, thumbs_down
    INTO upvotes, downvotes
    FROM post
    WHERE id = post_id
    

  • Use assignment to save the query result:

    post_id := (
      SELECT post_id
      FROM post
      WHERE user_id = 17
      LIMIT 1
    );
    

  • Use assignment to invoke a function:

    user_id := get_most_active_user();

  • PERFORM statement (in PL/pgSQL).

    PERFORM add_topic('Quick cakes');