source: music/triggers/insert_price_on_track_update.sql

CREATE OR REPLACE FUNCTION insert_price_on_track_update()
RETURNS TRIGGER AS
$$
BEGIN
    INSERT INTO price (value, date, track_id)
    VALUES (NEW.unit_price, NOW(), NEW.track_id);

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER insert_price_on_track_update
    AFTER UPDATE
    ON track
    FOR EACH ROW
EXECUTE FUNCTION insert_price_on_track_update();