gistfile1.sql

SELECT u.id, u.first_name, u.last_name, u.email, so.shipto_postal_code, so.placed_at
  FROM users u LEFT JOIN sales_orders so
    ON so.user_id = u.id
   AND so.state != 'pending'
 WHERE u.contact_me = 1
 ORDER BY u.id, so.placed_at DESC

----------------------------------

SELECT u.id, u.first_name, u.last_name, u.email, so1.shipto_postal_code, so1.placed_at
  FROM users u LEFT JOIN sales_orders so1
    ON so1.user_id = u.id
   AND so1.state != 'pending' LEFT JOIN sales_orders so2
    ON so2.user_id = u.id
   AND so2.state != 'pending'
   AND so2.placed_at > so1.placed_at
 WHERE u.contact_me = 1
   AND so2.id IS NULL
 ORDER BY u.id

----------------------------------

CREATE VIEW v_last_placed_order_per_user AS
SELECT user_id, MAX(placed_at) AS last_placed_at
  FROM sales_orders
 WHERE state != 'pending'
 GROUP BY user_id
 
SELECT u.id, u.first_name, u.last_name, u.email, so.shipto_postal_code
  FROM users u LEFT JOIN v_last_placed_order_per_user l
    ON l.user_id = u.id LEFT JOIN sales_orders so
    ON so.user_id = u.id AND so.placed_at = l.last_placed_at
 ORDER BY u.id