XML data type Functions – SQL Server

 The XML data type in MSSQL Server is a powerful tool for handling and manipulating XML data within a relational database system. In addition to storing XML data as a column in a table, SQL Server provides a number of XML functions and methods that allow for easy parsing, querying, and transformation of XML data. In this blog post, we will cover all XML data type methods available in MSSQL Server.

value() Method:

The value() method is used to extract a single value from an XML instance. This method accepts an XQuery expression as a parameter, which is used to identify the value to be extracted. The syntax of the value() method is as follows:

xml.value(XQuery expression, Data type)

For example, the following query extracts the value of the 'name' element from an XML column called 'MyXMLColumn':

SELECT MyXMLColumn.value('(/Root/Person/Name)[1]', 'varchar(50)') AS Name

FROM MyTable

 

query() Method:

The query() method is used to extract a set of nodes from an XML instance. This method also accepts an XQuery expression as a parameter, which is used to identify the nodes to be extracted. The syntax of the query() method is as follows:

xml.query(XQuery expression)

For example, the following query extracts all 'Person' nodes from an XML column called 'MyXMLColumn':

SELECT MyXMLColumn.query('/Root/Person') AS PersonNodes

FROM MyTable

 

exist() Method:

The exist() method is used to determine whether a specified node or set of nodes exists within an XML instance. This method returns a boolean value (true or false) indicating whether the specified nodes exist. The syntax of the exist() method is as follows:

xml.exist(XQuery expression)

For example, the following query checks whether the 'age' element exists within an XML column called 'MyXMLColumn':

SELECT MyXMLColumn.exist('/Root/Person/Age') AS AgeExists

FROM MyTable

 

modify() Method:

The modify() method is used to insert, delete, or update nodes within an XML instance. This method accepts an XQuery expression as a parameter, which is used to identify the nodes to be modified, as well as the modification operation to be performed. The syntax of the modify() method is as follows:

xml.modify(XQuery expression)

For example, the following query updates the value of the 'name' element within an XML column called 'MyXMLColumn':

UPDATE MyTable

SET MyXMLColumn.modify('replace value of (/Root/Person/Name)[1] with "John"')

WHERE ID = 1

 

nodes() Method:

The nodes() method is used to shred an XML instance into a set of rows, with each row representing a single node or set of nodes. This method accepts an XQuery expression as a parameter, which is used to identify the nodes to be shredded. The syntax of the nodes() method is as follows:

xml.nodes(XQuery expression)

For example, the following query shreds an XML column called 'MyXMLColumn' into a set of rows, with each row representing a single 'Person' node:

SELECT PersonNode.value('(Name)[1]', 'varchar(50)') AS Name,

       PersonNode.value('(Age)[1]', 'int') AS Age

FROM MyTable

CROSS APPLY MyXMLColumn.nodes('/Root/Person') AS Person(PersonNode)

In conclusion, MSSQL Server provides a powerful set of XML functions and methods for handling and manipulating XML data within a relational database system

Reference

https://learn.microsoft.com/en-us/sql/t-sql/xml/xml-data-type-methods?view=sql-server-ver16