Question

Hello Stack Overflow社区！我希望有人可以帮助传递一些建议，如果这个查询看起来没问题，是否有任何改进，以及我如何确定行是客户还是供应商。我已经在下面发布了我的代码，提前感谢您的帮助！

Northwind Traders的代表将在德国。管理层希望她在那里访问所有德国供应商和客户。提供德国所有供应商和客户的列表，包括联系人和地址。在报告中指定所列公司是客户还是供应商。

select *  
from
  Suppliers s
  inner join Products p
    on s.SupplierID = p.SupplierID
  inner join OrderDetails od
    on p.ProductID = od.ProductID
  inner join Orders o
    on od.OrderID = o.OrderID
  inner join Customers c
   on o.CustomerID = c.CustomerID
where
  (s.Country = 'Germany') 
  and (c.Country = 'Germany')

Answer 1

您应该单独获取供应商和客户详细信息，并使用UNION ALL进行合并。事实是，您需要在两个查询中使用相同的列别名，并将新列TYPE与 SUPPLIER 或 CUSTOMER 相应地引入，如下所示结构，

SELECT SUPPLIERS.NAME AS NAME
    ..
    ..
    , 'SUPPLIER' AS TYPE 
FROM SUPPLIERS 
WHERE COUNTRY = 'Germany'
UNION ALL
SELECT CUSTOMERS.NAME AS NAME
    ..
    ..
    , 'CUSTOMER' AS TYPE
FROM CUSTOMERS  
WHERE COUNTRY = 'Germany'

Answer 2

要仅解决一个Select而不使用SQL进行任何其他操作，您可以使用UNION获取供应商和客户的列：

select 'Supplier' partnerType, s.name, s.contact, s.address 
from Suppliers s inner join Products p on s.SupplierID = p.SupplierID
                 inner join OrderDetails od on p.ProductID = od.ProductID
                 inner join Orders o on od.OrderID = o.OrderID
where 
 (s.Country = 'Germany')
Union
Select 'Customer' partnerType, c.name, c.contact, c.address 
from Suppliers s inner join Products p on s.SupplierID = p.SupplierID
                 inner join OrderDetails od on p.ProductID = od.ProductID
                 inner join Orders o on od.OrderID = o.OrderID
                 inner join Customers c on o.CustomerID = c.CustomerID
where 
 (c.Country = 'Germany')

要确定是供应商还是客户，请仅使用列partnerType。

Answer 3

尝试 -

SELECT CustomerID AS ID,
       Customers.Contact AS Contact,
       Customers.Address AS Address,
       "Customer" AS Type
FROM Customers
WHERE Customers.Country = "Germany"
UNION
SELECT SupplierID,
       Suppliers.Contact,
       Suppliers.Address,
       "Supplier"
FROM Suppliers
WHERE Suppliers.Country = "Germany";

我不确定联系人或地址是一个字段还是多个字段。随意调整以适应桌子的结构。

我建议研究JOIN和UNION之间的差异。 UNION在此处有效，因为两个表中的详细信息具有相同的格式。

如何在sql查询中识别客户和供应商

3 个答案: