SQLITE-计算剩余项目数量

我有一个库存表，其中包含特定商品id/颜色的总商品数量：

库存表格

    item_code    |    colour    |    stock
---------------------------------------------
       A         |    red       |    10
       A         |    blue      |    8
       A         |    yellow    |    5
       B         |    red       |    5
       B         |    blue      |    0
       B         |    yellow    |    15

    order_id     |    item_code    |    colour    |    ordered_qty
----------------------------------------------------------------------
       1         |        A        |     red      |        3
       1         |        A        |     blue     |        1
       1         |        A        |     yellow   |        2
       1         |        B        |     red      |        1
       2         |        A        |     red      |        1
       2         |        A        |     yellow   |        3
       2         |        B        |     yellow   |        15

    item_code    |    colour    |    remaining
------------------------------------------------
       A         |    red       |    6
       A         |    blue      |    7
       A         |    yellow    |    0
       B         |    red       |    4
       B         |    blue      |    0
       B         |    yellow    |    0

然后我有一个表，其中存储了已订购的项目数量（请注意，相同的项目可以在不同的订单中找到）

订单\u表

    item_code    |    colour    |    stock
---------------------------------------------
       A         |    red       |    10
       A         |    blue      |    8
       A         |    yellow    |    5
       B         |    red       |    5
       B         |    blue      |    0
       B         |    yellow    |    15

    order_id     |    item_code    |    colour    |    ordered_qty
----------------------------------------------------------------------
       1         |        A        |     red      |        3
       1         |        A        |     blue     |        1
       1         |        A        |     yellow   |        2
       1         |        B        |     red      |        1
       2         |        A        |     red      |        1
       2         |        A        |     yellow   |        3
       2         |        B        |     yellow   |        15

    item_code    |    colour    |    remaining
------------------------------------------------
       A         |    red       |    6
       A         |    blue      |    7
       A         |    yellow    |    0
       B         |    red       |    4
       B         |    blue      |    0
       B         |    yellow    |    0

我需要创建一个保存剩余可用库存数量的表：例如，对于库存表中每个项目的数量，我需要从订单表中减去“已订购”数量，得到如下结果：

剩余_表

    item_code    |    colour    |    stock
---------------------------------------------
       A         |    red       |    10
       A         |    blue      |    8
       A         |    yellow    |    5
       B         |    red       |    5
       B         |    blue      |    0
       B         |    yellow    |    15

    order_id     |    item_code    |    colour    |    ordered_qty
----------------------------------------------------------------------
       1         |        A        |     red      |        3
       1         |        A        |     blue     |        1
       1         |        A        |     yellow   |        2
       1         |        B        |     red      |        1
       2         |        A        |     red      |        1
       2         |        A        |     yellow   |        3
       2         |        B        |     yellow   |        15

    item_code    |    colour    |    remaining
------------------------------------------------
       A         |    red       |    6
       A         |    blue      |    7
       A         |    yellow    |    0
       B         |    red       |    4
       B         |    blue      |    0
       B         |    yellow    |    0

我正在考虑使用一个视图，因为对于每个新插入的订单行，表都会自动更新。我能够获得每个项目/颜色的“已订购”数量：

SELECT item_code, colour, SUM(stock) as already_placed FROM orders_table GROUP BY item_code, colour

此查询将返回如下内容（请注意，B/blue从未订购过）：

现在，我一直在构建一个查询，该查询将在一个表或另一个视图中提供剩余的表数量

长话短说，我需要从原始的库存表中减去已经放置的数量，你能帮我吗？我在这里找不到任何“减法”或“减法”函数

有可能吗

---

提前感谢，请向您致意。

您可以将

库存表

与

订单表

合并，但在

订单表

中，您可以更改

订单数量

的符号。然后您可以按分组

差不多

SELECT item_code, colour, SUM(stock) as remaining FROM
(
    SELECT item_code, colour, stock FROM stock_table
    UNION ALL
    SELECT item_code, colour, -ordered_qty as stock FROM orders_table
)
GROUP BY item_code, colour

SQL Fiddle：

其他选择

SELECT sto.item_code, sto.colour, sto.in_stock - COALESCE(ord.already_placed, 0) AS remaining 
    FROM
        (SELECT item_code, colour, SUM(stock) AS in_stock FROM stock_table GROUP BY item_code, colour) sto
    LEFT JOIN
        (SELECT item_code, colour, SUM(ordered_qty) AS already_placed FROM orders_table GROUP BY item_code, colour) ord
        ON ord.item_code = sto.item_code AND ord.colour = sto.colour

在这里，

sto

和

ord

的

SELECT

可以放在两个视图中（一个是订购的库存总量，另一个是库存总量）

---

SQL Fiddle:

您可以将

库存表

和

订单表

合并，但在

订单表

中更改

订单数量

的符号。然后您可以

按

分组

差不多

SELECT item_code, colour, SUM(stock) as remaining FROM
(
    SELECT item_code, colour, stock FROM stock_table
    UNION ALL
    SELECT item_code, colour, -ordered_qty as stock FROM orders_table
)
GROUP BY item_code, colour

SQL Fiddle：

其他选择

SELECT sto.item_code, sto.colour, sto.in_stock - COALESCE(ord.already_placed, 0) AS remaining 
    FROM
        (SELECT item_code, colour, SUM(stock) AS in_stock FROM stock_table GROUP BY item_code, colour) sto
    LEFT JOIN
        (SELECT item_code, colour, SUM(ordered_qty) AS already_placed FROM orders_table GROUP BY item_code, colour) ord
        ON ord.item_code = sto.item_code AND ord.colour = sto.colour

在这里，

sto

和

ord

的

SELECT

可以放在两个视图中（一个是订购的库存总量，另一个是库存总量）

---

SQL FIDLE:

您可以使用相关子查询来计算已订购的特定项目的数量：

    item_code    |    colour    |    already_placed
----------------------------------------------------
       A         |    red       |    4
       A         |    blue      |    1
       A         |    yellow    |    5
       B         |    red       |    1
       B         |    yellow    |    15

CREATE VIEW remaining_view AS
SELECT item_code,
       colour,
       stock - (SELECT IFNULL(SUM(ordered_qty), 0)
                FROM orders_table
                WHERE orders_table.item_code = stock_table.item_code
                  AND orders_table.colour    = stock_table.colour)
       AS remaining
FROM stock_table

---

您可以使用相关子查询来计算订购了多少特定项目：

    item_code    |    colour    |    already_placed
----------------------------------------------------
       A         |    red       |    4
       A         |    blue      |    1
       A         |    yellow    |    5
       B         |    red       |    1
       B         |    yellow    |    15

CREATE VIEW remaining_view AS
SELECT item_code,
       colour,
       stock - (SELECT IFNULL(SUM(ordered_qty), 0)
                FROM orders_table
                WHERE orders_table.item_code = stock_table.item_code
                  AND orders_table.colour    = stock_table.colour)
       AS remaining
FROM stock_table

---

您可以使用自然左连接：

SELECT item_code, colour, IFNULL(q_stock - q_ordered, 0) as remaining
FROM (SELECT item_code, colour, SUM(stock) as q_stock FROM stock_table GROUP BY item_code, colour)
 NATURAL LEFT JOIN
 (SELECT item_code, colour, SUM(ordered_qty) as q_ordered FROM orders_table GROUP BY item_code, colour)

---

您可以使用自然左连接：

SELECT item_code, colour, IFNULL(q_stock - q_ordered, 0) as remaining
FROM (SELECT item_code, colour, SUM(stock) as q_stock FROM stock_table GROUP BY item_code, colour)
 NATURAL LEFT JOIN
 (SELECT item_code, colour, SUM(ordered_qty) as q_ordered FROM orders_table GROUP BY item_code, colour)