sql-server - 没有复制 xmlns:xsi 的 XML 路径元素 XSINIL

Question

我需要从表中提取 XML，值为空：

<RoomNo xsi:nil="true" />

所以我使用子句元素 xsinil：

for xml path('root'), elements xsinil

我的问题是提取由子查询组成的复杂 XML。子句元素 xsinil在每个子查询中插入代码xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

如果我删除内部元素 xsinil我会丢失空字段。

使用此查询：

    -- Test table
    CREATE TABLE #TestTable (StudentName VARCHAR(100), Course VARCHAR(100), Instructor VARCHAR(100), RoomNo VARCHAR(100))
    GO
    INSERT INTO #TestTable (StudentName, Course, Instructor, RoomNo)
    SELECT 'Mark', 'Algebra', 'Dr. James', '101'
    UNION ALL
    SELECT 'Mark', 'Maths', 'Dr. Jones', '201'
    UNION ALL
    SELECT 'Joe', 'Algebra', 'Dr. James', null
    UNION ALL
    SELECT 'Joe', 'Science', 'Dr. Ross', '301'
    UNION ALL
    SELECT 'Joe', 'Geography', 'Dr. Lisa', null
    UNION ALL
    SELECT 'Jenny', 'Algebra', 'Dr. James', '101'
    GO


    -- Xpath query
    select -- node STUDENT
        A.StudentName,
        (
            select -- node TEST
            Instructor as '@Instructor', Course as 'Course', RoomNo as 'RoomNo'
            from #TestTable B where B.StudentName = A.StudentName
            for xml path('test'), type, elements xsinil
            ) as 'node()'
    from (select distinct StudentName from #TestTable) A
    for xml path('student'), root('root'), type, elements xsinil

    -- end
    drop TABLE #TestTable

我有：

    <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <student>
        <StudentName>Jenny</StudentName>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo>101</RoomNo>
        </test>
      </student>
      <student>
        <StudentName>Joe</StudentName>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo xsi:nil="true" />
        </test>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. Ross">
          <Course>Science</Course>
          <RoomNo>301</RoomNo>
        </test>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. Lisa">
          <Course>Geography</Course>
          <RoomNo xsi:nil="true" />
        </test>
      </student>
      <student>
        <StudentName>Mark</StudentName>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo>101</RoomNo>
        </test>
        <test xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Instructor="Dr. Jones">
          <Course>Maths</Course>
          <RoomNo>201</RoomNo>
        </test>
      </student>
    </root>

但是我需要：

    <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
      <student>
        <StudentName>Jenny</StudentName>
        <test Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo>101</RoomNo>
        </test>
      </student>
      <student>
        <StudentName>Joe</StudentName>
        <test Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo xsi:nil="true" />
        </test>
        <test Instructor="Dr. Ross">
          <Course>Science</Course>
          <RoomNo>301</RoomNo>
        </test>
        <test Instructor="Dr. Lisa">
          <Course>Geography</Course>
          <RoomNo xsi:nil="true" />
        </test>
      </student>
      <student>
        <StudentName>Mark</StudentName>
        <test Instructor="Dr. James">
          <Course>Algebra</Course>
          <RoomNo>101</RoomNo>
        </test>
        <test Instructor="Dr. Jones">
          <Course>Maths</Course>
          <RoomNo>201</RoomNo>
        </test>
      </student>
    </root>