SELECT

  Customers.cust_name,

  total_price
FROM
(
    SELECT
      AMT.order_num,
      SUM(total_price) AS total_price
    FROM
(
        SELECT
          order_num,
          (item_price * quantity) AS total_price
        FROM
          OrderItems
      ) AS AMT
    GROUP BY
      AMT.order_num
  ) AS AMT1
  INNER JOIN Orders ON Orders.order_num = AMT1.order_num
  INNER JOIN Customers ON Customers.cust_id = Orders.cust_id
WHERE
  AMT1.total_price >= 1000