1. XML? What’s this doing in my database? Adam Koehler
SQL Saturday #901
Kansas City, MO
XML? What’s this doing in my database? Adam Koehler

2. THANK YOU, SPONSORS!

3. Surveys and late breaking information
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4. About Me: I have worked with SQL Server since 2000.
Adam Koehler
Senior Database Administrator at ScriptPro, LLC
I have worked with SQL Server since 2000.
Worked with versions 7.0 to 2017
LinkedIn:
Blog:

5. Topics What is XML? History of SQL Server Support
Storing XML in the database
Querying XML data
Manipulating XML in the database
Performance considerations
Demos
Q&A

6. XML, what is it? Stands for eXtensible Markup Language
Created in 1996, approved by W3C in 1998
Designed to store & transport data
Designed to be human and machine readable
Is defined by W3C standards
Used by different systems to for communication (HL7, RSS, ATOM,.NET)
Also used to describe data

7. Components of an XML document
Elements
Individual Parts of the XML
Come in pairs
The root element starts an XML document
Can contain text, attributes, other elements, or a combination of both
Can contain multiple values

8. Components of an XML document
Attributes
Can describe an element
Are always quoted
Cannot be a tree structure
Can only contain a single value

9. XML Document Definition
<?xml version=“1.0” encoding=“UTF-8”?>
<root>
<child></child>
<child>
<subchild>…</subchild>
</child>
</root>
<?xml version=“1.0” encoding=“UTF-8”?>
<car make=“Ford”>
<model>Taurus
<year>2013</year>
<Features>
<Engine>V6</Engine>
<Power>
<Seats>Driver</Seats>
<Windows>Yes</Windows>
</Power>
</Features>
<MSRP>25935</MSRP>
</model>
</car>

10. History of XML In SQL Server
support for generating XML result sets (FOR XML) and parsing/manipulating XML strings (OPENXML)
SQL 2005
Introduced the XML data type
XQuery support
XML DML support (Microsoft Specific)
Indexes on XML columns
SQL 2012
UTF 16 Support
Selective XML indexes

11. Storing XML in the database
Why?
Need original source version of data that is inserted into relational tables for auditing purposes
Source data structure changes rapidly, Allows for a single point of storage.
allows you to store in the database without having to change the schema constantly
The database itself contains the XML data, instead of individual files on disk, thus decreasing the amount of files that have to be backed up. Plus, the benefit of SQL Server and transactions. Backup the database, and you have the data.

12. How to store XML in the database
Can use the following data types:
(n)varchar(max)
XML
varbinary(max)

13. XML Data Type
Stores the XML data in a way that preserves the XML document structure and order
Can hold either untyped or typed XML
Has a 2GB size limit per row
Can be nested up to 128 levels
Cannot be compared or sorted
Can only be used with the ISNULL,COALESCE & DATALENGTH functions
Cannot explicitly be a key column in an index

14. Querying XML data Standard T-SQL statement:
SELECT Source_data_id,XML_Column FROM XML_Source_Data WHERE XML_Column LIKE '%string%'
XQuery:
SELECT Source_data_id
FROM XML_Source_Data
WHERE XML_Column.exist('//Inva lid_date') = 1

15. Manipulating XML Data
Can use XQuery to modify specific sections of an XML column
UPDATE XML_Source_Data SET XML_Column.modify('delete //Make[Ford]/Model[Pinto]'
WHERE Source_data_id = 123

16. Indexing XML Data Depends on how the XML is stored in the database
(max) data types
Can’t make (max) data types a key column on an index due to the 900 byte ceiling, but can be an included column on the index
XML data type
XML indexes do exist
Primary
Secondary
Selective XML indexes
Fulltext indexes
Can be used on both character and XML data types

17. XML Indexes – Primary
Must have a clustered index on the Primary Key column of the table before this can be created
Is a shredded representation of the BLOB data in the XML column
Each row in the index stores the following:
Tag name (element/attribute)
Value of the node
Node Type
Document order
Path from each node to the root of the XML tree (stored in the index in reverse order)
Primary key of the table the XML column is in

18. XML Indexes - Secondary
Must have a primary XML index first
Three types of secondary indexes
PATH
PROPERTY
VALUE

19. Secondary XML Indexes - Path
Best for queries that use exist() in the WHERE clause
Path and node values are key columns in this type of index, and querying for these will result in seeks against the index
SELECT Source_data_id
FROM XML_Source_Data
WHERE alid_date[.=" "]’) = 1

20. Secondary XML Indexes - Property
Works best when querying for objects with the value() method when a query is using the primary key column in the WHERE clause

21. Secondary XML Indexes - Value
Based on the node values in the Primary XML index
Is a good option when you’re looking for a specific value, but don’t know the element or attribute the value is associated to

22. Drawbacks to XML Indexes
They index the entire xml document
This leads to larger indexes, which in turn leads to larger database sizes
Index creation/maintenance takes longer
Xquery statements take longer because of the size of the indexes that have to be used

23. Selective XML Indexes Added in SQL Server 2012
When a selective index is created, the xml data path is shredded and stored in a normal table within SQL Server as a sparse column
Improvement over normal XML indexes
Allows for only a section of the XML document to be indexed, thus decreasing index size and maintenance times
Existing applications supplying the XML data do not have to be modified to support these indexes
Is not recommended for large numbers of node paths or for queries that look for elements in unknown locations

24. Selective XML Indexes – Details
Must have a clustered index on the primary key of the requisite table
Size of the PK cannot be more than 128 bytes
Clustering key cannot be more than 15 columns
Can only be created on a single XML column
Limited to the XML data type
Can have up to 249 selective indexes on a given table’s XML column
Each XML column can have one selective index
Cannot be used with query hints

25. Full-text & XML indexes, so happy together
Can use full-text indexes on XML data types alone, or in combination with XML indexes.
A full-text index will index the values of the XML data, but not the XML markup.

26. Metadata on XML indexes
Has a record in sys.indexes with index type 3
Dedicated DMV sys.xml_indexes
Using_xml_index
NULL for Primary XML index
References the Primary XML index for any Secondary indexes
Secondary_type
P – Path, V – Value, R – Property
Secondary_type_desc
Xml_index_type
0 – Primary, 1 – Secondary, 2 – Selective XML, 3 – Secondary Selective
XML_index_type_desc
Path_id
NULL for all indexes except for Secondary Selective
References sys.selective_xml_index_paths.Path_id

27. Metadata on XML indexes – There’s more!
sys.selective_xml_index_paths
Path – promoted path for the index
Path_type
0 – Xquery
1 – SQL
Xml_component_id
Unique id of the XML schema in the database

28. DEMOS!!!
AND Q&A

29. Links and References XML Data Type: http://bit.ly/2KrokJt
Selective Indexes:
Optimization Hints for Selective indexes:
Full-text index reference:
Using Full-text indexes with XML data:
XML DMV’s:

30. About Me: I have worked with SQL Server since 2000.
Adam Koehler
Senior Database Administrator at ScriptPro, LLC
I have worked with SQL Server since 2000.
Worked with versions 7.0 to 2017
LinkedIn:
Blog: