CREATE FUNCTION set_subscription(in_user_id int, in_subscription_type text, in_started date, in_expires date) RETURNS void
 LANGUAGE plpgsql
 STRICT
 AS $$
 BEGIN
 <<upsert>>
 LOOP
     UPDATE subscriptions
         SET (started, expires) = (in_started, in_expires)
         WHERE (user_id, subscription_type) = (in_user_id, in_subscription_type);
     EXIT upsert WHEN FOUND;
     BEGIN
         INSERT INTO subscriptions (user_id, subscription_type, started, expires)
             VALUES (in_user_id, in_subscription_type, in_started, in_expires);
         EXIT upsert;
     EXCEPTION WHEN unique_violation THEN
     END
 END LOOP;
 $$;