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Example: Specify the XMLTEXT directive

  • Artikkeli

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

This example illustrates how data in the overflow column is addressed by using the XMLTEXT directive in a SELECT statement using EXPLICIT mode.

Consider the Person table. This table has an Overflow column that stores the unconsumed part of the XML document.

USE tempdb;
GO
CREATE TABLE Person(PersonID varchar(5), PersonName varchar(20), Overflow nvarchar(200));
GO
INSERT INTO Person VALUES
    ('P1','Joe',N'<SomeTag attr1="data">content</SomeTag>')
   ,('P2','Joe',N'<SomeTag attr2="data"/>')
   ,('P3','Joe',N'<SomeTag attr3="data" PersonID="P">content</SomeTag>');

This query retrieves columns from the Person table. For the Overflow column, AttributeName isn't specified, but directive is set to XMLTEXT as part of providing a universal table column name.

SELECT 1 as Tag, NULL as parent,
       PersonID as [Parent!1!PersonID],
       PersonName as [Parent!1!PersonName],
       Overflow as [Parent!1!!XMLTEXT] -- No AttributeName; XMLTEXT directive
FROM Person
FOR XML EXPLICIT;

In the resulting XML document:

  • Because AttributeName isn't specified for the Overflow column and the xmltext directive is specified, the attributes in the <overflow> element are appended to the attribute list of the enclosing <Parent> element.

  • Because the PersonIDattribute in the <xmltext> element conflicts with the PersonID attribute retrieved on the same element level, the attribute in the <xmltext> element is ignored, even if PersonID is NULL. Generally, an attribute overrides an attribute of the same name in the overflow.

This is the result:

<Parent PersonID="P1" PersonName="Joe" attr1="data">content</Parent>
<Parent PersonID="P2" PersonName="Joe" attr2="data"></Parent>
<Parent PersonID="P3" PersonName="Joe" attr3="data">content</Parent>

If the overflow data has subelements and the same query is specified, the subelements in the Overflow column are added as the subelements of the enclosing <Parent> element.

For example, change the data in the Person table so that the Overflow column now has subelements.

USE tempdb;
GO
TRUNCATE TABLE Person;
GO
INSERT INTO Person VALUES
    ('P1','Joe',N'<SomeTag attr1="data">content</SomeTag>')
   ,('P2','Joe',N'<SomeTag attr2="data"/>')
    ,('P3','Joe',N'<SomeTag attr3="data" PersonID="P"><name>PersonName</name></SomeTag>');

If the same query is executed, the subelements in the <xmltext> element are added as subelements of the enclosing <Parent> element:

SELECT 1 as Tag, NULL as parent,
       PersonID as [Parent!1!PersonID],
       PersonName as [Parent!1!PersonName],
       Overflow as [Parent!1!!XMLTEXT] -- no AttributeName, XMLTEXT directive
FROM Person
FOR XML EXPLICIT;

This is the result:

<Parent PersonID="P1" PersonName="Joe" attr1="data">content</Parent>
<Parent PersonID="P2" PersonName="Joe" attr2="data"></Parent>
<Parent PersonID="P3" PersonName="Joe" attr3="data">
<name>PersonName</name>
</Parent>

If AttributeName is specified with the xmltext directive, the attributes of the <overflow> element are added as attributes of the subelements of the enclosing <Parent> element. The name specified for AttributeName becomes the name of the subelement

In this query, AttributeName, <overflow>, is specified together with the xmltext directive*:*

SELECT 1 as Tag, NULL as parent,
       PersonID as [Parent!1!PersonID],
       PersonName as [Parent!1!PersonName],
       Overflow as [Parent!1!overflow!XMLTEXT] -- Overflow is AttributeName
                      -- XMLTEXT is a directive
FROM Person
FOR XML EXPLICIT;

This is the result:

<Parent PersonID="P1" PersonName="Joe">
<overflow attr1="data">content</overflow>
</Parent>
<Parent PersonID="P2" PersonName="Joe">
<overflow attr2="data" />
</Parent>
<Parent PersonID="P3" PersonName="Joe">
<overflow attr3="data" PersonID="P">
<name>PersonName</name>
</overflow>
</Parent>

In this query element, directive is specified for PersonName attribute. This results in PersonName being added as a subelement of the enclosing <Parent> element. The attributes of the <xmltext> are still appended to the enclosing <Parent> element. The contents of the <overflow> element, subelements, are prepended to the other subelements of the enclosing <Parent> elements.

SELECT 1      AS Tag, NULL as parent,
       PersonID   AS [Parent!1!PersonID],
       PersonName AS [Parent!1!PersonName!element], -- element directive
       Overflow   AS [Parent!1!!XMLTEXT]
FROM Person
FOR XML EXPLICIT;

This is the result:

<Parent PersonID="P1" attr1="data">content<PersonName>Joe</PersonName>
</Parent>
<Parent PersonID="P2" attr2="data">
<PersonName>Joe</PersonName>
</Parent>
<Parent PersonID="P3" attr3="data">
<name>PersonName</name>
<PersonName>Joe</PersonName>
</Parent>

If the XMLTEXT column data contains attributes on the root element, these attributes aren't shown in the XML data schema and the MSXML parser doesn't validate the resulting XML document fragment. For example:

SELECT 1 AS Tag,
       0 AS Parent,
       N'<overflow a="1"/>' AS 'overflow!1!!xmltext'
FOR XML EXPLICIT, xmldata;

This is the result. In the returned schema, the overflow attribute a is missing from the schema:

<Schema name="Schema2"
xmlns="urn:schemas-microsoft-com:xml-data"
xmlns:dt="urn:schemas-microsoft-com:datatypes">
<ElementType name="overflow" content="mixed" model="open">`
</ElementType>`
</Schema>`
<overflow xmlns="x-schema:#Schema2" a="1">
</overflow>

See also