範例：指定 ELEMENTXSINIL 指示詞

適用於：SQL Server Azure SQL 資料庫 Azure SQL 受控執行個體

當您指定 ELEMENT 指示詞來擷取項目中心的 XML 時，如果資料行有 NULL 值，EXPLICIT 模式就不會產生與其對應的項目。 您可以在 xsi:nil 屬性設為值 TRUE 之處，選擇性地指定 ELEMENTXSINIL 指示詞，要求產生 NULL 值的元素。

以下查詢會建構包括員工地址在內的 XML。 對於 AddressLine2 及 City 資料行，資料行名稱會指定 ELEMENTXSINIL 指示詞。 這會在資料列集中，為 AddressLine2 及 City 資料行中的 NULL 值產生元素。

USE AdventureWorks2022;
GO
SELECT 1    as Tag,
       NULL as Parent,
       E.BusinessEntityID  as [Employee!1!EmpID],
       BEA.AddressID as [Employee!1!AddressID],
       NULL        as [Address!2!AddressID],
       NULL        as [Address!2!AddressLine1!ELEMENT],
       NULL        as [Address!2!AddressLine2!ELEMENTXSINIL],
       NULL        as [Address!2!City!ELEMENTXSINIL]
FROM   HumanResources.Employee AS E
INNER JOIN Person.BusinessEntityAddress AS BEA
    ON E.BusinessEntityID = BEA.BusinessEntityID

UNION ALL
SELECT 2 as Tag,
       1 as Parent,
       E.BusinessEntityID,
       BEA.AddressID,
       A.AddressID,
       AddressLine1,
       AddressLine2,
       City
FROM   HumanResources.Employee AS E
INNER JOIN Person.BusinessEntityAddress AS BEA
    ON E.BusinessEntityID = BEA.BusinessEntityID
INNER JOIN Person.Address AS A
    ON BEA.AddressID = A.AddressID
ORDER BY [Employee!1!EmpID],[Address!2!AddressID]
FOR XML EXPLICIT;

以下是部份結果：

<Employee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          EmpID="1"
          AddressID="249">
  <Address AddressID="249">
    <AddressLine1>4350 Minute Dr.</AddressLine1>
    <AddressLine2 xsi:nil="true" />
    <City>Minneapolis</City>
  </Address>
</Employee>
...

另請參閱

• 搭配 FOR XML 使用 EXPLICIT 模式