Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 16: A Brief XML Primer
So, to get rid of our ProductDescriptionSchemaCollectionSummaryRequired schema collection we
created earlier, we could execute:
DROP XML SCHEMA COLLECTION ProductDescriptionSchemaCollectionSummaryRequired;
And it’s gone.
XML Data Type Methods
The XML data type carries several intrinsic methods with it. These methods are unique to the XML data
type, and no other current data type has anything that is at all similar. The syntax within these methods
varies a bit because they are based on different, but mostly industry-standard, XML access methods. The
basic syntax for calling the method is standardized though:
.
There are a total of five methods available:
❑ .query: An implementation of the industry-standard XQuery language. This allows you to
access your XML by running XQuery-formatted queries. XQuery allows for the prospect that
you may be returning multiple pieces of data rather than a discrete value.
❑ .value: This one allows you to access a discrete value within a specific element or attribute.
❑ .modify: This is Microsoft’s own extension to XQuery. Whereas XQuery is limited to requesting
data (no modification language), the modify method extends XQuery to allow for data modification.
❑ .nodes: Used to break up XML data into individual, more relational-style rows.
❑ .exist: Much like the IF EXISTS clause we use extensively in standard SQL, the exist()
XML data type method tests to see whether a specific kind of data exists. In the case of exist(),
the test is to see whether a particular node or attribute has an entry in the instance of XML
you’re testing.
.query (SQL Server’s Implementation of XQuery)
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.query is an implementation of the industry standard XQuery language. The result works much like a
SQL query, except that the results are for matching XML data nodes rather than relational rows and
columns.
.query requires a parameter that is a valid XQuery to be run against your instance of XML data. For example,
if we wanted the steps out of the product documentation for ProductID 66, we could run the following:
SELECT ProductModelID, Instructions.query(‘declare namespace PI=”http://
schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions”;
/PI:root/PI:Location/PI:step’) AS Steps
FROM Production.ProductModel
WHERE ProductModelID = 66;
Note that the URL portion of the namespace declaration must be entered on a single line. They are
shown here word wrapped onto multiple lines because there is a limit to the number of characters we
can show per line in print. Make sure you include the entire URL on a single line.