Viewing relational data as XML

Using Microsoft SQL Server

Viewing relational data as XML 2

The ”FOR XML” clause

• SELECT comes with a ”FOR XML” clause• Example– SELECT * FROM student FOR XML RAW;– Output is an XML document

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Formatting options

• The XML output can be formatted in different ways– RAW– AUTO– EXPLICIT– PATH

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RAW formatting• Each row in the output becomes an XML element.

– Element name is ’row’– Table column names used as XML attribute names

• Example, simple– SELECT * FROM student FOR XML RAW;– Output

• <row studentID="1" studentname="John" />• <row studentID="2" studentname="Liz" />

• Example, joinSELECT d.departmentID, departmentName, teachernameFROM department d join teacher t ON d.departmentID = t.departmentID FOR XML

RAW– Output

<row departmentID="1" departmentName="Computer science" teachername="Anders" /><row departmentID="1" departmentName="Computer science" teachername="Peter L" /><row departmentID="1" departmentName="Computer science" teachername="Poul H" /><row departmentID="2" departmentName="Marketing" teachername="Lars" />No hierarchy!

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AUTO formatting• Each row in the output becomes an XML element.

– Table name used as XML element name• Example, simple

– SELECT * FROM student FOR XML AUTO;– Output

• <student studentID="1" studentname="John" />• <student studentID="2" studentname="Liz" />

• Example, joinSELECT d.departmentID, departmentName, teachernameFROM department d join teacher t ON d.departmentID = t.departmentID FOR XML AUTO– Output

<department departmentID="1" departmentName="Computer science"> <teacher teachername="Anders B" /> <teacher teachername="Peter L" /> …</department><department departmentID="2" departmentName="Marketing"> <teacher teachername="Lars" /> <teacher teachername="Poul" /></department>

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EXPLICIT formatting

• Gives you a lot of control over the output– Element names, attribute names, etc.

• Requires a lot of work!• Not used very often• May soon be deprecated

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PATH formatting

• A better way of doing EXPLICIT• Used for complex XML output• Based on XPath • Example, simple

– SELECT * FROM student FOR XML PATH;– Output

• <row>• <studentID>1</studentID>• <studentname>John</studentname>• </row>• Each row becomes an element (like RAW)• Each column becomes a child-element (unlike RAW)

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PATH formatting, continued

• Example– SELECT studentID as '@studentid', studentname FROM

student FOR XML PATH;– Output

• <row studentid="1">• <studentname>John</studentname>• </row>• <row studentid="2">• <studentname>Liz</studentname>• </row>• Columns names @xx becomes attributes in the XML output

• And much more XPath stuff …