Mysql 如何从具有相同列的两个表中从一列中减去

所以我有两个表名为：Stock和Order

表：库存

+-----------+-----------+
|   Item    |   Number  |
+-----------+-----------+
|   A       |      20   | 
|   B       |       7   |
|   C       |      11   | 
|   D       |      13   |
+-----------+-----------+

+-----------+-----------+
|   Item    |   Number  |
+-----------+-----------+
|   A       |      12   | 
|   B       |       5   |
|   C       |       6   | 
|   D       |       4   |
+-----------+-----------+

表：订单

+-----------+-----------+
|   Item    |   Number  |
+-----------+-----------+
|   A       |       8   | 
|   B       |       2   |
|   C       |       5   | 
|   D       |       9   |
+-----------+-----------+

我需要从库存到订单中减去列号

结果将是：

表：库存

+-----------+-----------+
|   Item    |   Number  |
+-----------+-----------+
|   A       |      20   | 
|   B       |       7   |
|   C       |      11   | 
|   D       |      13   |
+-----------+-----------+

+-----------+-----------+
|   Item    |   Number  |
+-----------+-----------+
|   A       |      12   | 
|   B       |       5   |
|   C       |       6   | 
|   D       |       4   |
+-----------+-----------+

我试过使用

SELECT item , number=
(
  (SELECT number FROM stock)-(SELECT number from order))
  FROM order;

不幸的是，它不工作，请帮助我！

---

请原谅格式化。

如果两个表处于1:1关系->请尝试以下操作：

SELECT B.Item,A.Number - B.Number FROM
Stock A
INNER JOIN Order B 
ON A.Item=B.Item

SELECT s.item, s.number - o.number
FROM stock s
JOIN order o
    ON s.item = o.item

否则：

SELECT s.item,
s.number - ISNULL(
    (SELECT SUM(o.number)
    FROM order o
    WHERE o.item = s.item), 0)
FROM stock s

---

如果两个表处于1:1关系->请尝试以下操作：

SELECT s.item, s.number - o.number
FROM stock s
JOIN order o
    ON s.item = o.item

否则：

SELECT s.item,
s.number - ISNULL(
    (SELECT SUM(o.number)
    FROM order o
    WHERE o.item = s.item), 0)
FROM stock s

---

提示：

JOIN

将两个表连接在一起。提示：

JOIN

将两个表连接在一起。