SELECT c.name AS category_name,
       p.name as product_name,
       pp.price
  FROM product_price pp
  JOIN product p
    ON p.product_id = pp.product_id
  JOIN category c
    ON c.category_id = p.category_id
 WHERE pp.price = (SELECT max (ppm.price)
                     FROM product pm
                     JOIN product_price ppm
                       ON ppm.product_id = pm.product_id
                    WHERE pm.category_id = p.category_id)
 ORDER BY c.name, p.name