Listnode和结构

Question

我有以下表结构：

客户：

CustomerId  Name            City
1           Richie Rich     MyCity
2           Bernie Bertel   MyTown

联系人：

ContactId   CustomerId  Name    Telephone
1           1           Test    123123

我想在XML结构中得到如下结果：

<Customers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Customers>
    <Name>Richie Rich</Name>
    <City>MyCity</City>
    <Contacts>
      <Contact xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
        <Name>Test</Name>
        <Telephone>123123</Telephone>
      </Contact>
    </Contacts>
  </Customers>
  <Customers>
    <Name>Bernie Bertel</Name>
    <City>MyTown</City>
    <Contacts xsi:nil="true" />
  </Customers>
</Customers>

相应的T-SQL查询是：

SELECT 
    Name,
    City,
    (
        SELECT 
            Name,
            Telephone
        FROM Contacts
        WHERE (Customers.CustomerId = Contacts.CustomerId)
        FOR XML PATH ('Contact'), TYPE, ELEMENTS XSINIL
    ) AS Contacts
FROM Customers
FOR XML AUTO, ROOT('Customers'), TYPE, ELEMENTS XSINIL

为了进一步处理，我必须知道列表节点的结构（Contact）。因此，如果客户没有联系人（如第二个条目中那样），我必须知道客户节点有哪些字段/列。

有谁知道如何解决这个问题？

Answer 1

如果我理解正确，那么如果没有联系人，你将不得不创建一个虚拟行;

SELECT 
    Name,
    City,
    (
        SELECT * FROM (
        SELECT 
            Name,
            Telephone
        FROM Contacts
        WHERE (Customers.CustomerId = Contacts.CustomerId)
        UNION ALL
        SELECT 
            NULL AS Name,
            NULL AS Telephone
        WHERE NOT EXISTS (SELECT 1 FROM Contacts WHERE Customers.CustomerId = Contacts.CustomerId)
        ) x
        FOR XML PATH ('Contact'), TYPE, ELEMENTS XSINIL
    ) AS Contacts
FROM Customers
FOR XML AUTO, ROOT('Customers'), TYPE, ELEMENTS XSINIL

产生这个;

<Customers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Customers>
    <Name>Richie Rich</Name>
    <City>MyCity</City>
    <Contacts>
      <Contact xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
        <Name>Test</Name>
        <Telephone>123123</Telephone>
      </Contact>
    </Contacts>
  </Customers>
  <Customers>
    <Name>Bernie Bertel</Name>
    <City>MyTown</City>
    <Contacts>
      <Contact xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
        <Name xsi:nil="true" />
        <Telephone xsi:nil="true" />
      </Contact>
    </Contacts>
  </Customers>
</Customers>