Functions on Nodes - namespace-uri
Applies to: 
SQL Server
Returns the namespace URI of the QName specified in $arg as a xs:string.
Syntax
fn:namespace-uri() as xs:string
fn:namespace-uri($arg as node()?) as xs:string
Arguments
$arg
Node name whose namespace URI part will be retrieved.
Remarks
If the argument is omitted, the default is the context node.
In SQL Server, fn:namespace-uri() without an argument can only be used in the context of a context-dependent predicate. Specifically, it can only be used inside brackets ([ ]).
If $arg is the empty sequence, the zero-length string is returned.
If $arg is an element or attribute node whose expanded-QName is not in a namespace, the function returns the zero-length string
Examples
This topic provides XQuery examples against XML instances stored in various xml type columns in the AdventureWorks database.
A. Retrieve namespace URI of a specific node
The following query is specified against an untyped XML instance. The query expression, namespace-uri(/ROOT[1]), retrieves the namespace URI part of the specified node.
set @x='<ROOT><a>111</a></ROOT>'
SELECT @x.query('namespace-uri(/ROOT[1])')
Because the specified QName does not have the namespace URI part but only the local name part, the result is a zero-length string.
The following query is specified against the Instructions typed xml column. The expression, namespace-uri(/AWMI:root[1]/AWMI:Location[1]), returns the namespace URI of the first <Location> element child of the <root> element.
SELECT Instructions.query('
declare namespace AWMI="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions" ;
namespace-uri(/AWMI:root[1]/AWMI:Location[1])') as Result
FROM Production.ProductModel
WHERE ProductModelID=7
This is the result:
https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions
B. Using namespace-uri() without argument in a predicate
The following query is specified against the CatalogDescription typed xml column. The expression returns all the element nodes whose namespace URI is https://www.adventure-works.com/schemas/OtherFeatures. The namespace-uri() function is specified without an argument and uses the context node.
SELECT CatalogDescription.query('
declare namespace p1="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
/p1:ProductDescription//*[namespace-uri() = "https://www.adventure-works.com/schemas/OtherFeatures"]
') as Result
FROM Production.ProductModel
WHERE ProductModelID=19
This is partial result:
<p1:wheel xmlns:p1="https://www.adventure-works.com/schemas/OtherFeatures">High performance wheels.</p1:wheel>
<p2:saddle xmlns:p2="https://www.adventure-works.com/schemas/OtherFeatures">
<p3:i xmlns:p3="http://www.w3.org/1999/xhtml">Anatomic design</p3:i> and made from durable leather for a full-day of riding in comfort.</p2:saddle>
...
You can change the namespace URI in the previous query to https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelWarrAndMain. You will then receive all the element node children of the <ProductDescription> element whose namespace URI part of the expanded QName is https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelWarrAndMain.
Implementation Limitations
These are the limitations:
- The namespace-uri() function returns instances of type xs:string instead of xs:anyURI.