Question

我希望标题不会太混乱 - 我不知道怎么称呼它。

想象一下，你有一张产品表：

+----+---------------------------+-------+
| id | name                      | stock |
+----+---------------------------+-------+
|  1 | 1. Product of set         |     2 |
|  2 | 2. Product of set         |     5 |
|  3 | 3. Product of set         |     3 |
|  4 | Set of Product 1, 2 and 3 |     0 |
+----+---------------------------+-------+

产品1-3可以全部销售，但也可以作为一套（产品4）销售。所以我们有另一张桌子：

+---------+-------------+-------+
| product | set_product | count |
+---------+-------------+-------+
|       1 |           4 |     1 |
|       2 |           4 |     2 |
|       3 |           4 |     1 |
+---------+-------------+-------+

......表示产品4由1x产品1,2x产品2和1x产品3组成。

在产品表中有一列“库存”，表示每种产品目前有多少库存。

问题是：我如何通过一个SELECT获得产品4的库存（当然这取决于产品1-3的库存）？

要设置测试用例，我创建了这段代码：

CREATE TABLE products (
    `id` int unsigned NOT NULL AUTO_INCREMENT, unique key(id),
    `name` TINYTEXT,
    `stock` int NOT NULL DEFAULT 0 
);

CREATE TABLE sets (
    `product` int unsigned NOT NULL,
    `set_product` int unsigned NOT NULL,
    `count` int NOT NULL
);

INSERT INTO products SET id=1, name="1. Product of set", stock=2;
INSERT INTO products SET id=2, name="2. Product of set", stock=5;
INSERT INTO products SET id=3, name="3. Product of set", stock=3;
INSERT INTO products SET id=4, name="Set of Product 1, 2 and 3";

INSERT INTO sets SET product=1, set_product=4, count=1;
INSERT INTO sets SET product=2, set_product=4, count=2;
INSERT INTO sets SET product=3, set_product=4, count=1;

Answer 1

试试这个

select p.name, ifnull(min(ps.stock / s.count), p.stock) as stock
from products as p
    left outer join sets as s on s.set_product = p.id
    left outer join products as ps on ps.id = s.product
group by p.name

SQL FIDDLE
你也可以做联合解决方案

select p.id, p.name, min(ps.stock / s.count) as stock
from products as p
    inner join sets as s on s.set_product = p.id
    inner join products as ps on ps.id = s.product
group by p.id, p.name

union all

select p.id, p.name, p.stock
from products as p
where p.id not in (select distinct tt.set_product from sets as tt)

SQL FIDDLE

Answer 2

您应该为所有套装产品选择最小库存。坚果你应该记住这个产品的集合数量：

 select 
       coalesce( min( p.stock / s.`count`), 0)
       as stock_product
 from 
   products p 
 left outer join
   sets s on
      p.id = s.product
 where
   set_product = 4

http://sqlfiddle.com/#!2/3be64/19/0

Answer 3

我会尝试这样的事情......（这是MS SQL，但它不应该离真相太远......）

SELECT DISTINCT s.set_product
              , ISNULL(MIN((p.stock/s.count)),0) calculated_stock
FROM [sets] s
INNER JOIN products p
  ON p.id = s.product
GROUP BY s.set_product;

MySql：从其他表和计数结果加入

3 个答案: