<pre class="c" name="code">
-- 自己掰測試資料
CREATE TABLE ithelp0520a(
id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
order_no CHAR(7) NOT NULL,
order_qty INT UNSIGNED NOT NULL,
UNIQUE (order_no)
);

INSERT INTO ithelp0520a(order_no, order_qty) VALUES
("001-001", 1000),
("001-002", 1200);

CREATE TABLE ithelp0520b(
id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
order_no CHAR(7) NOT NULL,
sale_no CHAR(7) NOT NULL,
sale_qty INT UNSIGNED,
FOREIGN KEY (order_no) REFERENCES ithelp0520a(order_no)
);

INSERT INTO ithelp0520b(order_no, sale_no, sale_qty) VALUES
("001-001", "002-001", 300),
("001-001", "002-002", 200),
("001-001", "002-003", 200),
("001-002", "002-004", 200),
("001-002", "002-004", 500);

--
SELECT a.order_no
     , a.order_qty
     , b.sale_no
     , b.sale_qty
     , (a.order_qty - c.sqty ) AS "non_delivery"
FROM ithelp0520a a
JOIN ithelp0520b b
ON a.order_no = b.order_no
JOIN (SELECT order_no, SUM(sale_qty) AS sqty
      FROM ithelp0520b
      GROUP BY order_no) c 
ON a.order_no = c.order_no
ORDER BY a.order_no, b.sale_no;

+----------+-----------+---------+----------+--------------+
| order_no | order_qty | sale_no | sale_qty | non_delivery |
+----------+-----------+---------+----------+--------------+
| 001-001  |      1000 | 002-001 |      300 |          300 |
| 001-001  |      1000 | 002-002 |      200 |          300 |
| 001-001  |      1000 | 002-003 |      200 |          300 |
| 001-002  |      1200 | 002-004 |      200 |          500 |
| 001-002  |      1200 | 002-004 |      500 |          500 |
+----------+-----------+---------+----------+--------------+

-- 使用補助變數來變化

SELECT e.order_no, e.order_qty, e.sale_no, e.sale_qty, e.non_delivery
FROM (SELECT IF(a.order_no = @lorder, "", a.order_no) AS "order_no"
      , IF(a.order_qty = @lqty, "" ,a.order_qty) AS "order_qty"
      , b.sale_no
      , b.sale_qty
      , IF((a.order_qty - c.sqty) = @lnon, "", (a.order_qty - c.sqty)) AS "non_delivery"
      , @lorder := a.order_no
      , @lqty := a.order_qty
      , @lnon := (a.order_qty - c.sqty)
FROM ithelp0520a a,
      ithelp0520b b,
    (SELECT order_no
	       , SUM(sale_qty) AS sqty
      FROM ithelp0520b
      GROUP BY order_no) c,
    (SELECT @lorder := NULL
	       , @lqty := NULL
	       , @lnon := NULL) d
WHERE a.order_no = b.order_no
AND   a.order_no = c.order_no
ORDER BY a.order_no, b.sale_no) e;

+----------+-----------+---------+----------+--------------+
| order_no | order_qty | sale_no | sale_qty | non_delivery |
+----------+-----------+---------+----------+--------------+
| 001-001  | 1000      | 002-001 |      300 | 300          |
|          |           | 002-002 |      200 |              |
|          |           | 002-003 |      200 |              |
| 001-002  | 1200      | 002-004 |      200 | 500          |
|          |           | 002-004 |      500 |              |
+----------+-----------+---------+----------+--------------+
5 rows in set (0.00 sec)

怎麼最近一堆只想問，不肯自己花時間思考的……
只會抄……不能自已變通一下嗎？