SQL Server - Querying and Managing XML Data

Polish SQL Server User Group
Querying and Managing XML Data
CHAPTER 7

About the Author
Marek Maśko
• Principal Database Analyst at Sabre
• Working with SQL Server for ~7 years
• SQL DBA, Dev & Architect
• MCP since 2012
• Contact Information:
Email: marek.masko@gmail.com
LinkedIn: https://pl.linkedin.com/in/marekmasko
Twitter: @MarekMasko

Agenda
• XML Introduction
• Returning Results As XML with FOR XML
• Querying XML Data with XQuery
• Using the XML Data Type

XML INTRODUCTION

Basic Example

Terminology
• A tag is a markup construct that begins with < and
ends with >. Tags come in three flavors:
start-tag, such as <section>;
end-tag, such as </section>;
empty-element tag, such as <line-break />.

Terminology
• An element is a logical document component that
either begins with a start-tag and ends with a
matching end-tag or consists only of an empty-
element tag. The characters between the start-tag
and end-tag, if any, are the element's content.
<greeting>Hello, world!</greeting>;
<line-break />.

Terminology
• An attribute is a markup construct consisting of a
name–value pair that exists within a start-tag or
empty-element tag.
<img src="madonna.jpg" alt="Madonna" />;
<step number="3">Connect A to B.</step>.
• An XML attribute can only have a single value and
each attribute can appear at most once on each
element.

XML
• Well-formed
• Ordered
• Case-sensitive Unicode
• Character data section
<![CDATA[ … ]]>
• Prolog
<?xml version="1.0" encoding="ISO-8859-15"?>
• XML Document vs XML Fragments

XML Namespace

XML Schema
• Standard to describe the metadata of XML
documents
• XML Schema Description (XSD) document
• Document validation
• Typed XML

RETURNING RESULTS AS XML
WITH FOR XML
Lesson 01

FOR XML clause
• Four modes:
–RAW
–AUTO
–PATH
–EXPLICIT

LESSON REVIEW

Question 1
• Which FOR XML options are valid? (Choose all that
apply.)
A. FOR XML AUTO
B. FOR XML MANUAL
C. FOR XML DOCUMENT
D. FOR XML PATH

Question 2
• Which directive of the FOR XML clause should you
use to produce element-centric XML?
A. ATTRIBUTES
B. ROOT
C. ELEMENTS
D. XMLSCHEMA

Question 3
• Which FOR XML options can you use to manually
format the XML returned? (Choose all that apply.)
A. FOR XML AUTO
B. FOR XML EXPLICIT
C. FOR XML RAW
D. FOR XML PATH

QUERYING XML DATA WITH XQUERY
Lesson 02

XQuery
• The standard language for browsing XML instances and
returning XML.
• XQuery is, like XML, case sensitive.
• XQuery returns sequences. Sequences can include atomic
values or complex values (XML nodes).
• Every identifier in XQuery is a qualified name, or a
QName. A QName consists of a local name and,
optionally, a namespace prefix.
• The SQL Server database engine processes XQuery inside
T-SQL statements through XML data type methods.

Sequences

XQuery Functions
• Numeric functions: ceiling(), floor(), round()
• String functions: concat(), contains(), substring(), string-
length(), lower-case(), upper-case()
• Boolean and Boolean constructor functions: not(), true(),
false()
• Nodes functions: local-name(), namespace-uri()
• Aggregate functions: count(), min(), max(), avg(), sum()
• Data accessor functions: data(), string()
• SQL Server extension functions: sql:column(),
sql:variable()

Navigation
• XPath expressions
• Every path consists of a sequence of steps
Node-name/child::element-name[@attribute-name=value]
• Step may consist of three parts:
– Axis Specifies the direction of travel. In the example, the axis is child::,
which specifies child nodes of the node from the previous step.
– Node test Specifies the criterion for selecting nodes. In the example,
element-name is the node test; it selects only nodes named element-
name.
– Predicate Further narrows down the search. In the example, there is
one predicate: [@attribute-name=value], which selects only nodes that
have an attribute named attribute-name with value value, such as
[@orderid=10952].

Axis

Node test
• A node test follows the axis you specify
• Possibilities:
– Simple node name
– Wildcard (*) = any principal node
• Node type tests:
– comment() Allows you to select comment nodes.
– node() True for any kind of node. Do not mix this with the asterisk
(*) wildcard; * means any principal node, whereas node() means
any node at all.
– processing-instruction() Allows you to retrieve a processing
instruction node.
– text() Allows you to retrieve text nodes, or nodes without tags.

Predicates
• Numeric – select nodes by position:
–/x/y[1]
–(/x/y)[1]
• Boolean – select nodes for which the predicate
evaluates to true

Value comparison operators

IF..THEN..ELSE
if (<expression1>)
then
<expression2>
else
<expression3>
• Like T-SQL CASE expression

FLWOR Expressions
• FOR - bind iterator variables to input sequences
• LET - assign a value to a variable for a specific
iteration
• WHERE - filter the iteration
• ORDER BY - control the order based on atomic values
• RETURN - format the resulting XML

Question 1
• Which of the following is not a FLWOR clause?
A. for
B. let
C. where
D. over
E. return

Question 2
• Which node type test can be used to retrieve all
nodes of an XML instance?
A. Asterisk (*)
B. comment()
C. node()
D. text()

Question 3
• Which conditional expression is supported in XQuery?
A. IIF
B. if..then..else
C. CASE
D. switch

USING THE XML DATA TYPE
Lesson 03

XML Data Type Methods
• query() – support querying
• value() – support retrieving atomic values
• exist() – support checking existence
• modify() – support modifying sections within the
XML data
• nodes() – support shredding XML data into
multiple rows in a result set

Using the XML Data Type for Dynamic Schema

XML Indexes
• XML can be up to 2GB of data
• Primary XML index – shredded persisted
representation of the XML values;
• Three types of Secondary XML indexes:
–PATH
–VALUE
–PROPERTY

Question 1
• Which of the following is not an XML data type
method?
A. merge()
B. nodes()
C. exist()
D. value()

Question 2
• What kind of XML indexes can you create? (Choose all
that apply.)
A. PRIMARY
B. PATH
C. ATTRIBUTE
D. PRINCIPALNODES

Question 3
• Which XML data type method do you use to shred
XML data to tabular format?
A. modify()
B. nodes()
C. exist()
D. value()

THANK YOU!

Resources
• Book: Training Kit Exam 70-461
• Scripts for Training Kit

SQL Server - Querying and Managing XML Data

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