WITH sales AS
(
SELECT 1 id, 9 menu_id, '무료 정책' sales_name
UNION ALL SELECT 2, 10, '유료 정책'
)
, menu AS
(
SELECT 9 id, '강남점 메뉴' menu_name
UNION ALL SELECT 10, '부산점 메뉴'
)
, product AS
(
SELECT 1 id, 10 menus_id, '바닐라라뗴' product_name
UNION ALL SELECT 2, 10, '딸기라떼'
)
SELECT s.id AS sale_id
     , s.sales_name
     , s.menu_id
     , m.menu_name
     , p.id AS product_id
     , p.product_name
  FROM sales s
  LEFT OUTER JOIN menu m
    ON s.menu_id = m.id
  LEFT OUTER JOIN product p
    ON m.id = p.menus_id
 WHERE s.id = 2
;
-- http://gurubee.net/lecture/1020