Returning XML Result Sets with SQL Server

Problem

With XML being used in so many application and data exchange capacities, extracting XML from SQL Server should not be a challenge.  Yet, some organizations are building complex applications to do so and overlooking some of the native SQL Server features.  If the data tier has a viable option to extract XML in a native format, should that option be considered?

Solution

Yes – Should be the resounding answer.  The trusted SELECT statement (SQL Server 2000 and SQL Server 2005) includes a FOR XML option (SQL Server 2000 and SQL Server 2005) with the ability to extract XML in a few different formats.  Each of these options offers a different means to format the XML. 

Why would I want to use the FOR XML options?

One of the strongest reasons to use one of the FOR XML options is that they are a simple extension to the trusted SELECT statement.  Regardless of the application, some sort of SELECT statement needs to be built, so adding the XML parameters is a no brainier.  Another consideration for choosing the FOR XML statement is that the SELECT statement can be called from a stored procedure, DTS\SSIS package or a script.  Finally, the FOR XML clause is supported in both SQL Server 2000 (with the exception of the XML PATH option) and 2005.

What are the differences between the FOR XML options?

IDOptionDescription
1FOR XML AUTOSimple nested tree of XML with each column being represented as a single element
2FOR XML RAWEach row in the result set is transformed into generic <row> element tag
3FOR XML EXPLICITA predefined XML format is created for the result set
4FOR XML PATHMuch of the same functionality as the EXPLICIT mode, but the elements and attributes can be built with XPATH like syntax

This option is not available in SQL Server 2000.

FOR XML AUTO

SQL Server 2000SQL Server 2005
SELECT TOP 1 a.au_lname AS ‘AuthorLastName’,
a.au_fname AS ‘AuthorFirstName’,
t.title AS ‘Title’,
t.pubdate AS ‘PublicationDate’
FROM dbo.Authors a
INNER JOIN dbo.TitleAuthor ta
ON a.au_id = ta.au_id
INNER JOIN dbo.Titles t
ON ta.title_id = t.title_id
WHERE a.state = ‘CA’
FOR XML AUTO		SELECT TOP 1 c.CourseName,
c.CourseDesc,
s.SectionTitle
FROM Course c
INNER JOIN Section s
ON c.CourseID = s.CourseID
FOR XML AUTO
<a AuthorLastName=”Green” AuthorFirstName=”Marjorie”><t Title=”The Busy Executive&apos;s Database Guide” PublicationDate=”1991-06-12T00:00:00″/></a><c CourseName=”DBMS-101″ CourseDesc=”Database fundamentals”><s SectionTitle=”MWF-8:00 AM”/></c>

FOR XML RAW

SQL Server 2000SQL Server 2005
SELECT TOP 1 a.au_lname AS ‘AuthorLastName’,
a.au_fname AS ‘AuthorFirstName’,
t.title AS ‘Title’,
t.pubdate AS ‘PublicationDate’
FROM dbo.Authors a
INNER JOIN dbo.TitleAuthor ta
ON a.au_id = ta.au_id
INNER JOIN dbo.Titles t
ON ta.title_id = t.title_id
WHERE a.state = ‘CA’
FOR XML RAW		SELECT TOP 1 c.CourseName,
c.CourseDesc,
s.SectionTitle
FROM Course c
INNER JOIN Section s
ON c.CourseID = s.CourseID
FOR XML RAW
<row AuthorLastName=”Green” AuthorFirstName=”Marjorie” Title=”The Busy Executive&apos;s Database Guide” PublicationDate=”1991-06-12T00:00:00″/><row CourseName=”DBMS-101″ CourseDesc=”Database fundamentals” SectionTitle=”MWF-8:00 AM”/> 

FOR XML EXPLICIT

SQL Server 2000SQL Server 2005
SELECT 1 AS Tag,
NULL AS Parent,
t.title AS [Title!1!TitleName],
NULL AS [LastName!2!AuthorLastName]
FROM dbo.Authors a
INNER JOIN dbo.TitleAuthor ta
ON a.au_id = ta.au_id
INNER JOIN dbo.Titles t
ON ta.title_id = t.title_id
WHERE a.state = ‘CA’
UNION ALL
SELECT 2 AS Tag,
1 AS Parent,
t.title,
a.au_lname
FROM dbo.Authors a
INNER JOIN dbo.TitleAuthor ta
ON a.au_id = ta.au_id
INNER JOIN dbo.Titles t
ON ta.title_id = t.title_id
WHERE a.state = ‘CA’
ORDER BY [Title!1!TitleName], [LastName!2!AuthorLastName]
FOR XML EXPLICIT		SELECT 1 AS Tag,
NULL AS Parent,
c.CourseName AS [Course!1!CourseName],
NULL AS [Section!2!SectionTitle]
FROM Course c
INNER JOIN Section s
ON c.CourseID = s.CourseID
WHERE c.CourseID = 1
UNION ALL
SELECT 2 AS Tag,
1 AS Parent,
c.CourseName,
s.SectionTitle
FROM Course c
INNER JOIN Section s
ON c.CourseID = s.CourseID
WHERE c.CourseID = 1
FOR XML EXPLICIT
<Title TitleName=”But Is It User Friendly?”> <LastName AuthorLastName=”Carson”/></Title> …<Course CourseName=”DBMS-101″> <Section SectionTitle=”MWF-8:00 AM” /> </Course>

FOR XML PATH

SQL Server 2000SQL Server 2005
Not availableSELECT c.CourseName,
c.CourseDesc,
s.SectionTitle
FROM Course c
INNER JOIN Section s
ON c.CourseID = s.CourseID
FOR XML PATH
Not available<row> <CourseName>DBMS-101</CourseName> <CourseDesc>Database fundamentals</CourseDesc> <SectionTitle>MWF-8:00 AM</SectionTitle> </row>

Next Steps

  • As you are faced with requirements to extract XML from your current systems, consider the SELECT FOR XML options as a viable means to complete the task.
  • If you have not had time to explore the many capabilities of XML, start with these simple examples and begin to make them more complex to meet your needs.
  • Stay tuned for more of SQL Server’s native XML capabilities…

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