XML in SQL Server 2005

Overview XML is a key part of any modern data environment It can be used to transmit data in a platform, application neutral form It can be used to store document type data that is not easily described in normal table structures SQL Server 2005 has many advanced xml features

Relational to XML SQL Server provides four methods to output relational data as XML –FOR XML RAW –FOR XML AUTO –FOR XML PATH –FOR XML EXPLICIT

For XML Raw Xml Raw is the easiest to use. With no other arguments it outputs an xml fragment with each column represented as an attribute, value pair. SELECT LastName, Firstname, HomePhone FROM Employees FOR XML RAW

XML RAW Results

Elements and Root To change the output you can use the “ELEMENTS” keyword to have the columns output as elements instead of attributes. You can also add a root element with the keyword “ROOT” so that the result is a well-formed XML file

EXAMPLE with ELEMENTS and ROOT SELECT LastName, Firstname, HomePhone FROM Employees FOR XML RAW('Employees'), ELEMENTS, ROOT('EmployeeList')

Limits of XML RAW All columns must be formatted in the same way—all attributes or all elements Only a one level hierarchy– no nested levels

For XML Auto XML Auto allows you to create nested structures SELECT CategoryName, ProductName, QuantityperUnit, unitprice FROM categories INNER JOIN Products ON Categories.CategoryID=Products.CategoryID FOR XML AUTO, ELEMENTS, ROOT('ProductCategories')

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For XML PATH XML Path provides full control over the XML and is easier than XML EXPLICIT SELECT CategoryName 'Category/CategoryName', ProductName 'Category/Product/ProductName', QuantityPerUnit 'Category/Product/QuantityPerUnit', UnitPrice 'Category/Product/price/data()' FROM categories INNER JOIN Products ON Categories.CategoryID=Products.CategoryID Order By CategoryName FOR XML PATH, ROOT('ProductCategories')

For XML Explicit Explict provides even more control over the xml but is complex to implement

Storing XML in the Database Xml can be stored in the database as either text or Starting with SQL Server 2005 as a native XML data type

As Text Advantages to saving as text –Preserves white space –Preserves xml declaration –Easily retrieved as a string and reconverted to xml Disadvantages –Can’t be searched directly –Can’t be directly updated –Can’t be tested against a schema

XML Data Type Limit 2Gbs Strips xml declaration Can be fragment or whole document Must be well formed Can be validated against a schema store in an XML Schema Collection

Validating XML (Schema Collections) Schema collects are stored in the server and can be used to validate columns with xml data types

XQuery SQL Server fully incorporates XQuery standards allowing a user to directly query xml content stored in the XML data type columns

SqlXml SQL XML, consists of a set of tools for processing and manipulating SQL server Data programmically