XML on SQL Server

XML on SQL Server
Kristian Torp
Department of Computer Science
Aalborg University
people.cs.aau.dk/˜torp
torp@cs.aau.dk
November 5, 2015
daisy.aau.dk
Kristian Torp (Aalborg University) XML on SQL Server November 5, 2015 1 / 69

Outline
1 Create and Insert
2 XML Queries
Saying Hello
exist()
query()
value()
nodes()
3 Generating XML from Select Statements
Raw
Auto
Path
4 Summary

Learning Goals
Goals
Overview of XML support on SQL Server
Storing XML directly SQL Server
Querying XML on SQL Server
Standard
Concepts are (fairly) general
Code is DBMS speciﬁc
DBMS Versions Tested
SQL Server 2008
SQL Server 2012

Create the Relational Schema
Example (Create the Table)
create table course (
id i n t primary key ,
dsc xml not n u l l )
Note
A create table statement as we know it
The XML data type named xml
A mixture of “old” data types int and new data types xml
The not-null constraint, just because we love them!

Insert Data
Example (Insert a Row)
i n s e r t i n t o course values (1 ,
’<courses>
<course id =”22” ects =”5” >
<name>XML</name>
<description >XPath and XQuery f o r querying XML documents
</ description >
</course>
<name>DB</name>
<description >Querying a r e l a t i o n a l database </ description >
</course>
</courses> ’ )
Note
A plain insert statement
The XML data type coersed from the text string

Insert Additional Row
Example (Insert another Row)
’<courses>
<course id =”44” ects =”10”>
<name>Imperative Programming </name>
<description >C and Pointers </ description >
</course>
<name>OOP</name>
<description >Working with classes and objects </ description >
</course>
</courses> ’ )
Note
Nothing new conceptually, simply an insert statement
We now have a small database!

Database Content
Example
id dsc
1
<courses>
<course id=” 22 ” ects=” 5 ”>
<name>XML</name>
<description>XPath . . . </ description>
</ course>
<name>DB</name>
<description>Querying . . . </ description>
</ course>
</ courses>
2
<courses>
<name>Imperative Programming</name>
<description>C . . . </ description>
</ course>
<name>OOP</name>
<description>Working . . . </ description>
</ course>
</ courses>

Not Well-formed XML
Example (Insert a Row)
’<course id =”77” ects =”10”>
<name>Object−Oriented Analysis and Design </name>
<description >Modeling with classes and objects </ description >
</course>
<name>Software Architecture </name>
<description >The big picture </ description >
</course> ’ )
Note
Has no root element
This works ﬁne!

Not Well-formed XML, cont.
Example (End tag is missing)
<name>Operating Systems </name>
<description >Linux , Windows , and so on</ description > ’ )
Note
XML parsing: line 3, character 61, unexpected end of input
Example (Fix the missing end tag)
<name>Operating Systems </name>
<description >Linux , Windows , and so on</ description >
</course> ’ )
Note
Works!

Not Well-formed XML, cont.
Example (Nesting Wrong)
’<course id =”13” ects =”5” >
<name><more>Compiler Construction </name></more>
<description >Lex and Yacc</ description >
</course> ’ )
Note
XML parsing: line 2, character 41, end tag does not match start tag
Example (“Weird” Cases)
i n s e r t i n t o course values (6 , ’ ’ )
i n s e r t i n t o course values (7 , ’NULL ’ )
Note
Works!
Example (Does this work?)
i n s e r t i n t o course values (8 ,NULL)

Summary: Create and Insert
Main Points
Create table has new XML data type
Very similar to the SQL/XML XML data type
Insert statement works as expected
XML documents, without root possible, tags must be matching
Delete works as expected
Not shown here
There is special support for updating XML columns
Updating only a part of the XML document in a cell

Recall the Database Content
Example
id dsc
1
<courses>
<name>XML</name>
</ course>
<name>DB</name>
</ course>
</ courses>
2
<courses>
</ course>
<name>OOP</name>
</ course>
</ courses>

Say Hello
Example (Use the Course Table)
select dsc . query ( ” l e t $s := ’ Hello , World ! ’ return $s ” )
from course
Note
This does not work!
And I used a long time to understand why not :-)
Example (Try Again (almost the same))
select dsc . query ( ’ l e t $s := ” Hello , World ! ” return $s ’ )
from course
Note
Works!
’ and “ are different!
dsc is a column on table course

Say Hello, cont
Example (Say Hello from XQuery)
select dsc . query ( ’ l e t $s := ” Hello , World ! ” return $s ’ )
from course
Example (Result)
(No column name)
Hello, World!
Hello, World!
Note
A hello for each row in the table
This is a simple XQuery
SQL Server generally follows the XQuery standard well

Say Hello, the T-SQL Way
Example (Use a Variable)
declare @x xml
select @x. query ( ’ l e t $s := ” Hello , World ! ” return $s ’ )
Example (Result)
(No column name)
null
Example (Initialize the Variable)
declare @x xml = ’ ’
select @x. query ( ’ l e t $s := ” Hello , World ! ” return $s ’ )
Example (Result)
(No column name)
Hello, World!

Document IDs with more than 5 ECTS Courses
Example (Use exist() in where )
select id
from course
where dsc . e x i s t ( ’ / / course [ @ects > 5] ’ )
Note
An expression of non-boolean type speciﬁed in a context where a
condition is expected, near ’)’
Example (Use exist() in select )
select id , dsc . e x i s t ( ’ / / course [ @ects > 5] ’ )
from course
Example (Result)
id (No column name)
1 0
2 1

Retrying Document IDs with more than 5 ECTS Courses
Example (Use exist() in where )
select id
from course
where dsc . e x i s t ( ’ / / course [ @ects > 5] ’ ) = 1
Example (Result)
id
2
Note
exist() returns 0, 1 or null
This is a surprise! (when used to other DBMSs)

Example
id dsc
1
<courses>
<name>XML</name>
</ course>
<name>DB</name>
</ course>
</ courses>
2
<courses>
</ course>
<name>OOP</name>
</ course>
</ courses>

XPath for ﬁnding Course Names
Example (Use XPath)
select dsc . query ( ’ / courses / course /name ’ ) as res
from course
Example (Result)
res
<name>XML</name>
<name>DB</name>
<name>OOP</name>
null
Note
What was expected, it is really XPath!
A null value for each row where the XPath has no match

XPath for ﬁnding Course Names in Text Format
Example (Use text())
select dsc . query ( ’ / courses / course /name/ t e x t ( ) ’ ) as res
from course
Example (Result)
res
XMLDB
Imperative ProgrammingOOP
Note
What was expected!
Not really useful in an SQL context

Accessing Attributes
Example (Look at Attributes)
select dsc . query ( ’ / courses / course / @ects ’ ) as res
from course
Note
XQuery [course.dsc.query()]: Attribute may not appear outside of an
element
Unexpected!
Example (Look at Attributes)
select dsc . query ( ’sum ( / courses / course / @ects ) ’ ) as res
from course
Example (Result)
res
10
15

More XPath
Example (Find 5 ECTS Courses)
select dsc . query ( ’ / courses / course [ @ects =5]/name/ t e x t ( ) ’ ) as res
from course
Example (Result)
res
XMLDB
OOP
Example (Filtering using where )
select dsc . query ( ’ / / course /name/ t e x t ( ) ’ ) as res
from course
where id = 1
Example (Result)
res
XMLDB

Multi-Column XPath
Example (More than One Column)
select dsc . query ( ’ / / course /name ’ ) as name,
dsc . query ( ’ / / course / description ’ ) as descr
from course
Example (Result)
name descr
<name>XML</name>
<name>DB</name>
<name>Imperative . . . </name>
<name>OOP</name>
<description>C and Pointers</ description>

Multi-Column XPath with text()
Example (Multiple Columns and text())
select dsc . query ( ’ / / course /name/ t e x t ( ) ’ ) as name,
dsc . query ( ’ / / course / description / t e x t ( ) ’ ) as descr
from course
Example (Result)
name descr
XMLDB XPath ... Querying ...
Imperative Programming OOP C and Pointers Working ...

Full FLWOR
Example (FLWOR Query)
select dsc . query ( ’ f o r $c in / / course
where $c / @ects >= 5
return ( $c /name, $c / description ) ’ ) as res
from course
Example (Result)
res
<name>XML</name>
<description>XPath and XQuery f o r querying XML documents</ description>
<name>DB</name>
<description>Querying a r e l a t i o n a l database</ description>
<description>C and Pointers</ description>
<name>OOP</name>
<description>Working with classes and objects</ description>

Example
id dsc
1
<courses>
<name>XML</name>
</ course>
<name>DB</name>
</ course>
</ courses>
2
<courses>
</ course>
<name>OOP</name>
</ course>
</ courses>

Get Course Names in a Relational Fashion
Example (Using the value() Function)
select dsc . value ( ’ / / course /name ’ , ’ nvarchar (30) ’ )
from course
Note
XQuery [course.dsc.value()]: ’value()’ requires a singleton (or empty
sequence), found operand of type ’xdt:untypedAtomic *’
Example (Singleton’ing)
select dsc . value ( ’ ( / / course /name ) [ 1 ] ’ , ’ nvarchar (30) ’ )
from course
Example (Result)
(No column name)
XML
Imperative Programming

Retrying Get Course Names in a Relational Fashion
Example (First)
select dsc . value ( ’ ( / / course [ 1 ] / name ) [ 1 ] ’ , ’ nvarchar (30) ’ )
from course
Example (Result)
(No column name)
XML
Example (Last)
select dsc . value ( ’ ( / / course /name ) [ l a s t ( ) ] ’ , ’ nvarchar (30) ’ )
from course
Example (Result)
(No column name)
DB
OOP

Value and Wrong SQL Data Type
Example (First)
from course
Example (Result)
(No column name)
XML
Example (Last)
from course
Example (Result)
(No column name)
XML
Imp

value() and Wrong SQL Data Type, cont.
Example (String as an Integer)
select dsc . value ( ’ ( / / course /name ) [ 1 ] ’ , ’ i n t ’ )
from course
Note
Conversion failed when converting the nvarchar value ’XML’ to data
type int.
Example (Integer Attribute)
select dsc . value ( ’ ( / / course / @ects ) [ 1 ] ’ , ’ i n t ’ )
from course
Example (Result)
(No column name)
5
10

Flattening using value()
select id ,
dsc . value ( ’ ( / / course / @ects ) [ 1 ] ’ , ’ i n t ’ ) as ects
from course
where dsc . e x i s t ( ’ / / course [ @ects > 5] ’ ) = 1
Example (Result)
id ects
2 10
Note
Using value() and exist() functions in same query
Still too few rows

Flattening using value(), cont
select dsc . value ( ’ ( / / course / @id ) [ l a s t ( ) ] ’ , ’ i n t ’ ) as cid ,
dsc . value ( ’ ( / / course /name ) [ l a s t ( ) ] ’ , ’ nvarchar (30) ’ ) as cname ,
dsc . value ( ’ ( / / course / description ) [ l a s t ( ) ] ’ , ’ nvarchar (50) ’ ) as
dsc . value ( ’ ( / / course / @ects ) [ l a s t ( ) ] ’ , ’ i n t ’ ) as ects
from course
Example (Result)
cid cname dsc ects
11 DB Querying... 5
55 OOP Working... 5
Note
Pure relational world result
Result only has two rows (should have four)
value() cannot be used must use nodes()

Flattening using nodes()
Example (Flatten XML)
select f l a t . course . value ( ’ ( . / @id ) [ 1 ] ’ , ’ i n t ’ ) as cid ,
f l a t . course . value ( ’ ( . / name ) [ 1 ] ’ , ’ varchar (50) ’ ) as cname ,
f l a t . course . value ( ’ ( . / description ) [ 1 ] ’ , ’ varchar (50) ’ ) as dsc ,
f l a t . course . value ( ’ ( . / @ects ) [ 1 ] ’ , ’ i n t ’ ) as ects
from course
cross apply dsc . nodes ( ’ / / course ’ ) f l a t ( course )
order by cid
Example (Result)
cid cname dsc ects
11 DB Querying... 5
22 XML XPath... 5
44 Imp. C and ... 10
55 OOP Working... 5
Note
Relational view on XML data!!!

Hide XML
Example (Create a View on XML Data)
create view coursexml flat as
select f l a t . course . value ( ’ ( . / @id ) [ 1 ] ’ , ’ i n t ’ ) as cid ,
f l a t . course . value ( ’ ( . / name ) [ 1 ] ’ , ’ varchar (50) ’ ) as cname ,
f l a t . course . value ( ’ ( . / description ) [ 1 ] ’ , ’ varchar (50) ’ ) as dsc ,
f l a t . course . value ( ’ ( . / @ects ) [ 1 ] ’ , ’ i n t ’ ) as ects
from course
cross apply dsc . nodes ( ’ / / course ’ ) f l a t ( course )
Example (Query the View)
select ∗
from coursexml flat
where ects = 5 and cid > 20
order by cid
Example (Result)
cid cname dsc ects
22 XML XPath... 5
55 OOP Working... 5

Summary: Queries
Functions
Function Descrition
exist() Check for existence
query() XPath and XQuery
value() Extract single value
nodes() For ﬂatting nodes
modify() For (ﬁne grained) updates of XML
Note
SQL Server only
SQL/XML via programming languages

Master-Detail Example I
Order
id
customer name
amount
OrderLine
lineno
price per unit
quan. desc.
has
Assumptions
An order cannot exist without order lines
Amount is the sum of the amount of order lines for a give order
Must be larger than zero
Derived from order lines but stored because often queried
Order line is a weak entity

Master-Detail Example II
Example
create table oorder (
oid i n t primary key ,
cname varchar (30) not n u l l )
Example
create table oorder line (
oid i n t not null ,
line no i n t not n u l l check ( line no > 0) ,
dsc varchar (50) not null ,
quantity i n t not n u l l check ( quantity > 0) ,
price each numeric (6 ,2) not n u l l check ( price each > 0.0) ,
c o n s t r a i n t ol pk primary key ( oid , line no ) ,
c o n s t r a i n t o l o f k foreign key ( oid )
references oorder ( oid ) )

Get XML Out
Example
select ∗
from oorder
f o r xml raw
Example (Result)
<row oid=” 11 ” cname=”Anna” />
<row oid=” 22 ” cname=” Benny ” />
<row oid=” 33 ” cname=” Curt ” />
Note
A select statement
The for xml raw is SQL Server speciﬁc
Pretty ugly format ;-)

Get Elements Out
Example
select ∗
from oorder
f o r xml raw , elements
Example (Result)
<row>
<oid>11</ oid>
<cname>Anna</ cname>
</ row>
<row>
<oid>22</ oid>
<cname>Benny</ cname>
</ row>
<row>
<oid>33</ oid>
<cname>Curt</ cname>
</ row>
Note
Much nicer

Rename Element Names
Example
select oid as ” order −id ” ,
cname as ” customer−name”
from oorder
Example (Result)
<row>
<order −id>11</ order −id>
<customer−name>Anna</ customer−name>
</ row>
<row>
<customer−name>Benny</ customer−name>
</ row>
snip
Note
A select statement
The for xml raw is SQL Server speciﬁc

Rename Enclosed Element
Example
from oorder
f o r xml raw ( ’ customer ’ ) , elements
Example (Result)
<customer>
</ customer>
<customer>
<customer−name>Curt</ customer−name>
</ customer>
Note
All columns are elements
Missing a root element

Adding a Root Element
Example
from oorder
f o r xml raw ( ’ customer ’ ) , elements , root ( ’ customers ’ )
Example (Result)
<customers>
<customer>
</ customer>
<customer>
<customer−name>Curt</ customer−name>
</ customer>
</ customers>
Note
Now nice XML document

Joining Tables
Example
select ∗
from oorder , oorder line
where oorder . oid = oorder line . oid
Example (Result (snip))
<row>
<oid>11</ oid>
<cname>Anna</ cname>
<oid>11</ oid>
<line no>1</ line no>
<dsc>Cola</ dsc>
<quantity>1</ quantity>
<price each>10.00</ price each>
</ row>
Note
No nesting

Summary: Raw
Overview
Fast to get XML fragments out
Nice simple extension to select statement
Default output in attributes
Either all attributes or all elements
Mixture of attributes and elements hard
Is a bit “raw”
Additional options, type, xmldata, xmlschema

Get XML Out
Example
select ∗
from oorder
f o r xml auto
Example (Result)
<row oid=” 11 ” cname=”Anna” />
<row oid=” 22 ” cname=” Benny ” />
<row oid=” 33 ” cname=” Curt ” />
Note
At ﬁrst glanse looks like for xml raw
But wait, there is more ...

The Power of Auto
Example
select ∗
and oid < 30
f o r xml auto
Example (Result)
<oorder oid=” 11 ” cname=”Anna”>
<o order line oid=” 11 ” line no =” 1 ” dsc=” Cola ” quantity =” 1 ” price each=” 10.00 ”
<o order line oid=” 11 ” line no =” 2 ” dsc=” Chips ” quantity =” 1 ” price each=” 15.00
</ oorder>
<oorder oid=” 22 ” cname=” Benny ”>
<o order line oid=” 22 ” line no =” 1 ” dsc=” Cola ” quantity =” 1 ” price each=” 10.00 ”
<o order line oid=” 22 ” line no =” 2 ” dsc=” Burger ” quantity =” 2 ” price each=” 20.0
<o order line oid=” 22 ” line no =” 3 ” dsc=” Chips ” quantity =” 1 ” price each=” 15.00
</ oorder>
Note
Does automatic nesting at “natural” levels

Rename Elements
Example
select oorder . oid as ” order ” ,
oorder . cname as ” customer ” ,
oorder line . dsc as ” description ” ,
oorder line . quantity ,
oorder line . price each as ” price ”
f o r xml auto
<oorder order=” 11 ” customer=”Anna”>
<o order line description =” Cola ” quantity =” 1 ” price=” 10.00 ” />
<o order line description =” Chips ” quantity =” 1 ” price=” 15.00 ” />
</ oorder>
<oorder order=” 22 ” customer=” Benny ”>
<o order line description =” Cola ” quantity =” 1 ” price=” 10.00 ” />
<o order line description =” Burger ” quantity =” 2 ” price=” 20.00 ” />
<o order line description =” Chips ” quantity =” 1 ” price=” 15.00 ” />
</ oorder>

Add Root Element + Rename
Example
select ” order ” . oid as ” id ” ,
” order ” . cname as ” customer ” ,
” l i n e ” . dsc as ” description ” ,
” l i n e ” . quantity ,
” l i n e ” . price each as ” price ”
from oorder as ” order ” , oorder line as ” l i n e ”
where ” order ” . oid = ” l i n e ” . oid
f o r xml auto , root ( ’ orders ’ )
<orders>
<order id=” 11 ” customer=”Anna”>
<l i n e description =” Cola ” quantity =” 1 ” price=” 10.00 ” />
<l i n e description =” Chips ” quantity =” 1 ” price=” 15.00 ” />
</ order>
<order id=” 22 ” customer=” Benny ”>
<l i n e description =” Cola ” quantity =” 1 ” price=” 10.00 ” />
<l i n e description =” Burger ” quantity =” 2 ” price=” 20.00 ” />
<l i n e description =” Chips ” quantity =” 1 ” price=” 15.00 ” />
</ order>
</ orders>

Make it All Elements
Example
select ” order ” . oid as ” id ” ,
” order ” . cname as ” customer ” ,
” l i n e ” . dsc as ” description ” ,
” l i n e ” . quantity ,
” l i n e ” . price each as ” price ”
from oorder as ” order ” , oorder line as ” l i n e ”
where ” order ” . oid = ” l i n e ” . oid
f o r xml auto , elements , root ( ’ orders ’ )
<orders>
<order>
<id>11</ id>
<customer>Anna</ customer>
<l i n e>
<description>Cola</ description>
<price>10.00</ price>
</ l i n e>
snip

Summary: Auto
Overview
Fast to get XML out even for joins
Row tag can only be renamed by table alias
Okay at getting nesting correct
Either attributes or elements
Options similar as for the xml raw output

Get XML Out
Example
select oorder . oid as ” id ” ,
oorder line . line no as ” lineno ” ,
f o r xml path
<row>
<id>11</ id>
<lineno>1</ lineno>
</ row>

Adding Structure
Example
select oorder . oid as ” id ” ,
oorder line . line no as ” lineno ” ,
f o r xml path ( ’ order ’ ) , root ( ’ orders ’ )
<orders>
<order>
<id>11</ id>
<lineno>1</ lineno>
</ order>
<order>

Adding Attributes and Nesting Line Items
Example
select oorder . oid as ”@id” ,
oorder line . line no as ” l i n e / lineno ” ,
oorder line . dsc as ” l i n e / description ” ,
oorder line . quantity as ” l i n e / quantity ” ,
oorder line . price each as ” l i n e / price ”
<orders>
<order id=” 11 ”>
<l i n e>
<lineno>1</ lineno>
</ l i n e>
</ order>

Nesting Correctly
Example
select oorder . oid as ”@id” ,
( select oorder line . line no as ” @lineno ” ,
oorder line . quantity as ” quantity ” ,
from oorder line
f o r xml path ( ’ l i n e ’ ) , type )
from oorder
<orders>
<order id=” 11 ”>
<l i n e lineno=” 1 ”>
</ l i n e>

Summary: Auto
Overview
More complicated than raw and auto mode
Nesting “correctly” by subqueries
Cast to XML type otherwise a string!
Relies on naming conventions for attributes versus elements
Options similar as for the raw and auto modes

Summary
Summary
XPath follows the standard
XQuery follows the standard
XML support on SQL Server far from standard!
Not Looked At (RTFM :-))
Indexing XML columns
Updates
Querying XML from C#
SQLXML (Microsoft speciﬁc)

Additional Information
Web Sites
Introduction to XQuery in SQL Server 2005
Good overview, cannot ﬁnd a newer
msdn.microsoft.com/en-us/library/ms345122(v=sql.90).aspx
XML Options in Microsoft SQL Server 2005
More on the XML data type, cannot ﬁnd a newer
msdn.microsoft.com/en-us/library/ms345110%28v=sql.90%29.
aspx
SQLXML 4.0 Programming Concepts
Good tutorial
Must be installed separately on SQL Server 2008 and above
msdn.microsoft.com/en-us/library/ms171779.aspx
FOR XML (SQL Server)
SQL Server 2012
http://msdn.microsoft.com/en-us/library/ms178107.aspx

XML on SQL Server

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