Question

我们有三张桌子。

1） Product_Table

Product_ID
Product_Name

2） Warehouse1_Table

Product_ID
Inventory1

3） Warehouse2_Table

Product_ID
Inventory2

Warehouse1_Table或Warehouse2_Table中可能不存在产品ID 。

我正在尝试找出一个可以提供类似内容的查询：

Product_ID, Product_Name, TotalStock

如果Product_ID在两个表中，则TotalStock是Inventory1 + Inventory2。
如果Product_ID在Warehouse1_Table中，则TotalStock是Inventory1 如果Product_ID在Warehouse2_Table中，则TotalStock是Inventory2 如果Product_ID不在任何仓库表中，则TotalStock为0

Answer 1

这样的事可能有用。我添加了一些示例数据来说明我的目标：

 create table Product_table
(Product_ID int unsigned primary key,Product_Name varchar(50) not null,
UNIQUE KEY `Product_TableUIdx1` (Product_Name));

create table Warehouse1_Table
(Product_ID int unsigned not null,Inventory1 int,
UNIQUE KEY `Warehouse1_Table_UIdx1` (Product_Id));

create table Warehouse2_Table
(Product_ID int unsigned,Inventory2 int,
UNIQUE KEY `Warehouse2_Table_UIdx1` (Product_Id));

insert into Product_table values (1,"Banana");
insert into Product_table values (2,"Apple");
insert into Product_table values (3,"Pear");
insert into Product_table values (4,"Orange");

insert into Warehouse1_Table values (1,2);

insert into Warehouse2_Table values (3,10);
insert into Warehouse2_Table values (4,5);
insert into Warehouse2_Table values (1,3);

select pt.Product_ID,pt.Product_Name,
ifnull(wt1.Inventory1,0)+ifnull(wt2.Inventory2,0) as StockTotal
from Product_table pt
left outer join Warehouse1_Table wt1 on wt1.Product_ID = pt.Product_ID
left outer join Warehouse2_Table wt2 on wt2.Product_ID = pt.Product_ID;

感谢Dems的鹰眼指出，避免在Warehouse1_Table或Warehouse1_Table中为同一Product_ID的多行引起的重复是很重要的。如果无法像上面的DDL那样添加唯一键，那么您可以使用（有点丑陋）查询来解决这个问题：

select pt.Product_ID,pt.Product_Name,
ifnull(wt1.Inventory1Total,0)+ifnull(wt2.Inventory2Total,0) as StockTotal
from Product_table pt
left outer join (select w1.Product_ID,sum(w1.Inventory1) as Inventory1Total
from Warehouse1_Table w1 group by w1.Product_ID) as wt1 on wt1.Product_ID = pt.Product_ID
left outer join (select w2.Product_ID,sum(w2.Inventory2) as Inventory2Total
from Warehouse2_Table w2 group by w2.Product_ID) as wt2 on wt2.Product_ID = pt.Product_ID;

Answer 2

尝试使用LEFT JOIN，如果您的交叉表没有产生匹配，那么这是一个不会破坏您的查询的连接。然后总结一下清单，如下：

SELECT p.Product_ID, p.Product_Name,
(IFNULL(w1.Inventory1, 0) + ISNULL(w2.Inventory2, 0)) AS TotalStock
FROM `Product_Table` AS p
LEFT JOIN `Warehouse1_Table` AS w1 ON (
    p.Product_ID = w1.Product_ID
) LEFT JOIN `Warehouse2_Table` AS w2 ON (
    p.Product_ID = w2.Product_ID
);

然后，您的结果集应包含“TotalStock”字段，其中包含组合库存或其中一个仓库返回的库存。

Answer 3

SELECT Product_ID,
       Product_Name,
       SUM(w1.Inventory1) as sum1,
       SUM(w2.Inventroy2) as sum2           

FROM Product_Table p
LEFT JOIN Warehouse1_Table w1 ON p.Product_ID = w1.Product_ID
LEFT JOIN Warehouse2_Table w2 ON p.Product_ID = w2.Product_ID
GROUP BY p.Product_ID

我没有测试过，但这就是想法。

Answer 4

SELECT Product_ID, Product_Name, 
       Inventory1 + Inventory2 AS TotalStock
  FROM Product_Table 
       NATURAL JOIN Warehouse1_Table
       NATURAL JOIN Warehouse2_Table
UNION
SELECT Product_ID, Product_Name, 
       Inventory1 AS TotalStock
  FROM Product_Table 
       NATURAL JOIN Warehouse1_Table
 WHERE Product_ID NOT IN (
                          SELECT Product_ID 
                            FROM Warehouse2_Table
                         )
UNION
SELECT Product_ID, Product_Name, 
       Inventory2 AS TotalStock
  FROM Product_Table 
       NATURAL JOIN Warehouse2_Table
 WHERE Product_ID NOT IN (
                          SELECT Product_ID 
                            FROM Warehouse1_Table
                         )
UNION
SELECT Product_ID, Product_Name, 
       0 AS TotalStock
  FROM Product_Table 
 WHERE Product_ID NOT IN (
                          SELECT Product_ID 
                            FROM Warehouse1_Table
                         )
       AND Product_ID NOT IN (
                              SELECT Product_ID 
                                FROM Warehouse2_Table
                             );

用MySQL中的1个密钥查询2个以上的表？

4 个答案: