Microsoft SQL Server 2008 R2 Unleashed- P191 pptx

ptg 1894 CHAPTER 47 Using XML in SQL Server 2008 But this statement succeeds: INSERT XmlExample SELECT ‘<root><foo/></root>’ Let’s say you manage the data for a company that has just upgraded from SQL Server 2000 to 2008. You already store all your XML inside ntext columns, and it’s time to convert those columns to xml. You can do this easily if the stored XML is well formed, as in the following example: CREATE TABLE NTextXml ( NTextXmlColumn ntext NULL ) GO INSERT NTextXml SELECT ‘<feedback_review> <parts_order id=”106”> <customer_comment>Lot&apos;s of Junk!</customer_comment> </parts_order> </feedback_review>’ GO ALTER TABLE NTextXml ALTER COLUMN NTextXmlColumn xml NULL Next, you would like to ensure that all your XML validates against a schema. To change the column from typed to untyped XML by associating a schema, you execute the following: ALTER TABLE NTextXml ALTER COLUMN NTextXmlColumn xml (DOCUMENT HumanResources.HRResumeSchemaCollection) go XML Validation: Declaration not found for element ‘feedback_review’. Location: /*:feedback_review[1] The statement has been terminated. Notice the error generated. The reason is that the tags used are not defined in the schemas of HRResumeSchemaCollection, so the XML does not validate, and the ALTER TABLE statement fails. What you really want is for the XML to validate against your own schema, which is described in the next section. Using XML Schema Collections In this section, you define a simple XML schema, add it to a new schema collection stored on the server, and create a table where you can store instances of this schema. You also add a check constraint to ensure that the value of the ProductId attribute of the XML’s root node matches the value of the ProductId column, using the xml data type value() method (discussed later in this chapter, in the section, “The Built-in xml Data Type ptg 1895 Using the xml Data Type 47 Methods”). The foreign key constraint you define on ProductId also serves to ensure that both ProductId values reference a primary key value in HumanResources.Product. The real-world concept behind this sample schema is that it defines groups of customer feedback calls and subsequent corporate responses pertaining to different kinds of orders. Listing 47.14 shows the schema and table definition. LISTING 47.14 An XSD and Table for Modeling and Storing Customer Feedback Reviews use AdventureWorks2008 go CREATE XML SCHEMA COLLECTION Sales.FeedbackSchemaCollection AS ‘<?xml version=”1.0”?> <xsd:schema xmlns:xsd=”http://www.w3.org/2001/XMLSchema” targetNamespace=”urn:www-samspublishing-com:examples:feedback_review_xsd” xmlns=”urn:www-samspublishing-com:examples:feedback_review_xsd” elementFormDefault=”qualified” attributeFormDefault=”unqualified”> <xsd:element name=”feedback_review” type=”feedbackReviewType”/> <xsd:complexType name=”feedbackReviewType”> <xsd:sequence minOccurs=”1” maxOccurs=”unbounded”> <xsd:element name=”order” type=”orderType”/> </xsd:sequence> <xsd:attribute name=”product_id” type=”xsd:integer” use=”optional”/> </xsd:complexType> <xsd:complexType name=”feedbackType” mixed=”true”> <xsd:attribute name=”id” type=”xsd:integer” use=”required”/> </xsd:complexType> <xsd:complexType name=”orderType”> <xsd:choice minOccurs=”0” maxOccurs=”unbounded”> <xsd:element name=”customer_comment” type=”feedbackType”/> <xsd:element name=”company_response” type=”feedbackType”/> </xsd:choice> <xsd:attribute name=”id” type=”xsd:integer” use=”required”/> <xsd:attribute name=”type” use=”required”> <xsd:simpleType> <xsd:restriction base=”xsd:string”> <xsd:enumeration value=”parts”/> <xsd:enumeration value=”product”/> <xsd:enumeration value=”service”/> </xsd:restriction> </xsd:simpleType> ptg 1896 CHAPTER 47 Using XML in SQL Server 2008 </xsd:attribute> </xsd:complexType> </xsd:schema>’ GO CREATE FUNCTION Sales.fnCheckProductId ( @FeedbackReviewXml xml ) RETURNS int AS BEGIN DECLARE @ProductId int SELECT @ProductId = @FeedbackReviewXml.value(‘ declare namespace fr=”urn:www-samspublishing-com:examples:feedback_review_xsd”; /fr:feedback_review[1]/@product_id’, ‘int’) RETURN @ProductId END GO CREATE TABLE Sales.FeedbackReview ( FeedbackReviewId int IDENTITY(1, 1) NOT NULL PRIMARY KEY, ProductId int NULL REFERENCES Production.Product, FeedbackReviewXml xml (DOCUMENT Sales.FeedbackSchemaCollection) NOT NULL, CONSTRAINT ProductIdMatches CHECK (Sales.fnCheckProductId(FeedbackReviewXml) = ProductId) ) GO Having created the xml column, you can now insert valid, well-formed documents into FeedbackReview in the following manner: INSERT Sales.FeedbackReview SELECT NULL, ‘<feedback_review xmlns=”urn:www-samspublishing-com:examples:feedback_review_xsd”> <order id=”353” type=”service”> <customer_comment id=”131”> You guys said you&apos;d be here on Monday. </customer_comment> <company_response id=”242”>I said Wednesday!</company_response> </order> ptg 1897 Using the xml Data Type 47 </feedback_review>’ GO (1 row(s) affected) Using INSERT, you can input XML into xml columns as varchar, xml, or literal string data, or you can insert the output of a subquery that returns these types. The syntax used to create an XML schema collection is simple and straightforward: CREATE SCHEMA COLLECTION schema_collection_name AS schema The schema parameter can be either a string (as shown), or a variable that contains the text of the schema of type varchar, nvarchar, varbinary, nvarbinary, or xml. Dropping a schema collection is just as easy: DROP SCHEMA COLLECTION schema_collection_name If you ever want to select your schema back out again, you simply call the system func- tion xml_schema_namespace, as in the following example: SELECT xml_schema_namespace( ‘Sales’, ‘FeedbackSchemaCollection’, ‘urn:www-samspublishing-com:examples:feedback_review_xsd’ ) To add additional schemas to the collection, you use ALTER XML SCHEMA COLLECTION: ALTER XML SCHEMA COLLECTION Sales.FeedbackSchemaCollection ADD another schema To view some of the nodes in your stored XML schemas, you query sys.xml_schema_collection and its related catalog views. Here’s an example: use AdventureWorks2008 go SELECT el.name, el.*, el.must_be_qualified FROM sys.columns sc JOIN sys.xml_schema_collections xs ON sc.xml_collection_id = xs.xml_collection_id JOIN sys.xml_schema_elements el ON xs.xml_collection_id = el.xml_collection_id WHERE sc.name = ‘FeedbackReviewXml’ Given the name of the table’s typed xml column (FeedbackReviewXml), you can find its associated schema collection by querying the catalog views as follows: SELECT sc.name XmlColumnName, ptg 1898 CHAPTER 47 Using XML in SQL Server 2008 xs.name CollectionName, ns.name Namespace from sys.columns sc JOIN sys.xml_schema_collections xs ON sc.xml_collection_id = xs.xml_collection_id JOIN sys.xml_schema_namespaces ns ON ns.xml_collection_id = sc.xml_collection_id WHERE sc.name = ‘FeedbackReviewXml’ go XmlColumnName CollectionName Namespace FeedbackReviewXml FeedbackSchemaCollection urn:www-samspublishing- com:examples:feedback_review_xsd You can accomplish the same thing by using the Object Browser in SSMS by viewing the properties of the xml column or by right-clicking the Modify menu choice on the table object, as shown in Figure 47.1. You can control permissions on schema collections by using the standard ALTER, CONTROL, TAKE OWNERSHIP, REFERENCES, VIEW DEFINITION, and EXECUTE syntax. Here’s an example: GRANT ALTER ON XML SCHEMA COLLECTION::Sales.FeedbackSchemaCollection TO some_login FIGURE 47.1 Viewing the properties of an xml column in SSMS. ptg 1899 Using the xml Data Type 47 There are a few unsupported XML schema features in schema collections. Check the Books Online article titled “Guidelines and Limitations of XML Schema Collections on the Server” for the most up-to-date information. Following are some notable limitations: . The XSD constraints key, keyref, and unique are not supported. . XSD include and redefine are not supported. . Lax validation is not supported. You can also manage XML schema collections using SSMS. To do so, you open the Object Browser and expand the main tree to the following node: ServerName\Databases\AdventureWorks2008\Programmability\Types\XML Schema Collections. Then you right-click a schema collection to drop it or to add new schemas. You can also easily script schemas out for review whenever needed. Figure 47.2 shows the expanded Object Browser tree. The Built-in xml Data Type Methods Now that you know how to create and manage typed and untyped xml columns, the next step is to learn how to query and modify stored XML content. Although SQL Server supports only a subset of the XQuery 1.0 recommendation, you’ll soon see that it’s plenty to get the job done. FIGURE 47.2 Using the Object Browser to manage XML schema collections. ptg 1900 CHAPTER 47 Using XML in SQL Server 2008 Keep in mind that a mastery of XQuery is not a requirement for selecting out XML data; you can just specify the name of the xml column to select all the data back at once. SQL Server provides five built-in methods on the xml data type: query(), exists(), value(), nodes(), and modify(). These methods are appended to the name of the xml column in question, using the ColumnName.MethodName([MethodParameters]) syntax. These methods work on XML in the following ways: . query()—Evaluates an XQuery expression into a node list, allowing for reshaping of the selected nodes. Results in untyped XML. . exists()—Performs a Boolean test to see whether the result of an XQuery expres- sion is empty (no matching nodes). Returns 1 (non-empty), or 0 (empty). . value()—Extracts a single (that is, scalar) value from an XML node and casts it to a SQL Server relational data type (for example, int, varchar). . nodes()—Uses an XQuery expression to decompose the XML input into a rowset; this is similar to the effect of OPENXML. . modify()—Alters the content of an XML document using the insert, replace value of, and delete XQuery functions. XQuery is a bit like T-SQL in that it uses similar SELECT-FROM-WHERE-ORDER BY semantics to find the required nodes. It also bears a resemblance to writing foreach loops with object iterators in a language such as C#. It is unique in that it combines the navigational power of XPath to locate nodes and (in the same expressions) allows for new XML genera- tion on the fly, all in one tight syntax package built especially for processing XML. To use XQuery effectively, you need to have at least a rudimentary understanding of XPath. A great starting point is the World Wide Web Consortium’s (W3C’s) site, at www. w3.org/TR/xpath20/. The following subsections assume such basic knowledge. Selecting XML by Using query() The job of query() is to retrieve XML nodes by using XQuery expressions. The result of query() is an instance of untyped xml. It takes a single parameter, a string literal contain- ing the XQuery code itself. NOTE Like all the other four xml data type methods (and unlike most other T-SQL keywords), query() is case sensitive. This is in keeping with the case sensitivity of XML itself. NOTE The parameter to query() cannot be a variable; it must be a string literal. This puts something of a hold on dynamic XQuery expressions. However, declared T-SQL variables and column values are available for use in XQuery, using the functions sql:variable() and sql:column() (described later in this chapter). ptg 1901 Using the xml Data Type 47 Each XQuery query is broken into two distinct parts, separated by a semicolon. The first part is known as the prolog. This is the place where any namespaces used in the XPath expressions and selected nodes are declared. The second part is known as the body, and this is the place where XPath and XQuery expressions are evaluated. The following example declares the act namespace in its query prolog and then selects any act:eMail nodes from Person.Person.AdditionalContactInfo in its body: SELECT AdditionalContactInfo.query( ‘ declare namespace act=”http://schemas.microsoft.com/sqlserver/2004/07/adventure- works/ContactTypes”; //act:eMail ‘ ) FROM Person.Person WHERE ContactId = 2 go <act:eMail xmlns:act=”http://schemas.microsoft.com/sqlserver/2004/07/adventure- works/ContactTypes”> <act:eMailAddress>Joe@xyz.com</act:eMailAddress> <act:SpecialInstructions> Dont send emails for urgent issues. Use telephone instead. </act:SpecialInstructions> </act:eMail> Note that as with FOR XML, the result of query() can sometimes be an XML fragment (or an empty string). You can again use FOR XML RAW, ROOT to guarantee that this won’t happen. Listing 47.15 illustrates this use, as well as the WITH XMLNAMESPACES statement. LISTING 47.15 Using WITH XMLNAMESPACES with FOR XML and query() WITH XMLNAMESPACES ( ‘http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ContactTypes’ as act ) SELECT FirstName, LastName, AdditionalContactInfo.query( ‘ //act:eMail ‘ ptg 1902 CHAPTER 47 Using XML in SQL Server 2008 ) FROM Person.Person WHERE BusinessEntityID = 2 FOR XML RAW(‘ContactInfo’), ROOT(‘Contact’) go <Contact xmlns:act=”http://schemas.microsoft.com/sqlserver/2004/07/adventure- works/ContactTypes”> <ContactInfo FirstName=”Catherine” LastName=”Abel”> <act:eMail xmlns:act=”http://schemas.microsoft.com/sqlserver/2004/07/ adventure-works/ContactTypes”> <act:eMailAddress>Joe@xyz.com</act:eMailAddress> <act:SpecialInstructions> Dont send emails for urgent issues. Use telephone instead. </act:SpecialInstructions> </act:eMail> </ContactInfo> </Contact> You can use WITH XMLNAMESPACES to declare namespaces for use in subsequent SELECT statements. Using this statement makes it possible to omit the prolog from the query(). It also has the desirable side effect of adding the act namespace declaration to the root Contact node in the resulting FOR XML RAW wrapper. It’s a great keystroke saver and helps keep xml data type queries readable. In addition to selecting nodes with simple XPath expressions, you can use query() to specify WHERE clause conditions on the selected nodes, iterate through the nodes using for-each semantics, order the nodes differently than in the original document, and return XML in any desired structure, based on the selection. This type of processing is known by its acronym FLWOR (pronounced flower), which stands for for, let, where, order by, return. The for Clause The for clause establishes a variable that is bound to a node list for the purpose of iterating over each node. In each iteration of the for loop, this bound variable takes the value of the context node. It may be optionally typed (using as XML_Schema_TypeName) to a schema-declared type, and it is followed by the XPath used to match the nodes to be selected. The bound variable in the following example is $ContextNode: SELECT Instructions.query(‘ declare default element namespace “http://schemas.microsoft.com/sqlserver/2004/07/adventure -works/ProductModelManuInstructions”; for $ContextNode in //Location return <LotSize> {$ContextNode/@LotSize} </LotSize> ptg 1903 Using the xml Data Type 47 ‘) as Result FROM Production.ProductModel WHERE ProductModelID = 10 Go <LotSize xmlns=”http://schemas.microsoft.com/sqlserver/2004/07/adventure- works/ProductModelManuInstructions” LotSize=”100” /> This example also shows the use of the declare default element namespace statement, which allows the specified XPath expressions that follow it to omit any namespace prefixes. In place of an XPath expression, you can use the bound variable to iterate through a sequence of values, rather than nodes, as in the following example: SELECT Instructions.query(‘ for $ContextNode in (1, 2, 3) return <Number> {$ContextNode } </Number> ‘) as Result FROM Production.ProductModel WHERE ProductModelID = 10 go <Number>1</Number> <Number>2</Number> <Number>3</Number> You can also specify more than one bound variable in the for clause. Bound variables subsequent to the first can be used in XPath queries against the first. In this manner, two related context nodes—one inner and one outer—can be created simultaneously. This is analogous to writing a nested for loop in a programming language, but here you need only declare both context variables by using a comma. Here’s an example: DECLARE @Xml xml SET @Xml = ‘ <outernode name=”a”> <innernode>1</innernode> <innernode>2</innernode> <innernode>3</innernode> </outernode> <outernode name=”b”> <innernode>4</innernode> <innernode>5</innernode> <innernode>6</innernode> </outernode> ‘ SELECT @Xml.query(‘ . namespace act=”http://schemas .microsoft. com/sqlserver/2004/07/adventure- works/ContactTypes”; //act:eMail ‘ ) FROM Person.Person WHERE ContactId = 2 go <act:eMail xmlns:act=”http://schemas .microsoft. com/sqlserver/2004/07/adventure- works/ContactTypes”> <act:eMailAddress>Joe@xyz.com</act:eMailAddress> <act:SpecialInstructions> Dont. XMLNAMESPACES ( ‘http://schemas .microsoft. com/sqlserver/2004/07/adventure-works/ContactTypes’ as act ) SELECT FirstName, LastName, AdditionalContactInfo.query( ‘ //act:eMail ‘ ptg 1902 CHAPTER 47 Using XML in SQL Server 2008 ) FROM. xmlns:act=”http://schemas .microsoft. com/sqlserver/2004/07/adventure- works/ContactTypes”> <ContactInfo FirstName=”Catherine” LastName=”Abel”> <act:eMail xmlns:act=”http://schemas .microsoft. com/sqlserver/2004/07/ adventure-works/ContactTypes”> <act:eMailAddress>Joe@xyz.com</act:eMailAddress> <act:SpecialInstructions> Dont