XML (eXtensible Markup Language) is a widely used format for storing and exchanging data. In SQL Server, XML can be stored in memory and processed to make the data and metadata available for querying. This article will explain the process of preparing XML in SQL Server and how to retrieve data from XML using the OpenXML function.

Preparing XML in Memory

In order to work with XML data in SQL Server, it needs to be stored in memory. This involves declaring an XML variable and setting it equal to the XML data. Additionally, a document handle (or “claim ticket”) is obtained using the sp_XML_PrepareDocument stored procedure. This handle is required to refer to the XML document later.

For example:

DECLARE @Doc XML
SET @Doc = '<root><element1>Value1</element1><element2>Value2</element2></root>'

DECLARE @hDoc INT
EXEC sp_XML_PrepareDocument @Doc, @hDoc OUTPUT

SELECT @hDoc AS HandleNumber

After running the code, the handle number (or claim ticket) will be displayed. This handle is used to access the stored XML document.

Retrieving Data from XML using OpenXML

The OpenXML function in SQL Server provides a rowset view of the XML data stored in memory. It allows you to query the data in a structured format, similar to a table. The function requires the document handle and a rowpattern hint to specify the desired data.

Here is an example:

DECLARE @hDoc INT
SET @hDoc = 1

SELECT ProductID, Quantity
FROM OPENXML (@hDoc, '/root/element2')
WITH (ProductID INT, Quantity INT)

In this example, the rowpattern hint ‘/root/element2’ narrows the query to the attributes found at the ‘element2’ level of the XML document. The SELECT statement retrieves the ProductID and Quantity values from this level.

By using the WITH clause, you can specify the field names and their data types. This allows you to shred the data at a single element level.

It is important to note that the XML document and handle should be used carefully to avoid creating multiple instances and unnecessary memory usage.

Conclusion

XML processing in SQL Server involves storing XML data in memory and using the OpenXML function to retrieve the desired data. By understanding the process of preparing XML and using the appropriate rowpattern hints, you can effectively query and manipulate XML data in SQL Server.

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