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position Function (XQuery)

Returns an integer value that indicates the position of the context item within the sequence of items currently being processed.


fn:position() as xs:integer

In SQL Server, fn:position() can only be used in the context of a context-dependent predicate. Specifically, it can only be used inside brackets ([ ]).Comparing against this function does not reduce the cardinality during static type inference.

This topic provides XQuery examples against XML instances that are stored in various xml type columns in the AdventureWorks database. For an overview of each of these columns, see xml Data Type Representation in the AdventureWorks Database.

A. Using the position() XQuery function to retrieve the first two product features

The following query retrieves the first two features, the first two child elements of the <Features> element, from the product model catalog description. If there are more features, it adds a <there-is-more/> element to the result.

SELECT CatalogDescription.query('
     declare namespace pd="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
     <Product> 
          { /pd:ProductDescription/@ProductModelID }
          { /pd:ProductDescription/@ProductModelName } 
          {
            for $f in /pd:ProductDescription/pd:Features/*[position()<=2]
            return
            $f 
          }
          {
            if (count(/pd:ProductDescription/pd:Features/*) > 2)
            then <there-is-more/>
            else ()
          } 
     </Product>        
') as x
FROM Production.ProductModel
WHERE CatalogDescription is not null

Note the following from the previous query:

  • The namespace keyword in the XQuery Prolog defines a namespace prefix that is used in the query body.
  • The query body constructs XML that has a <Product> element with ProductModelID and ProductModelName attributes, and has product features returned as child elements.
  • The position() function is used in the predicate to determine the position of the <Features> child element in context. If it is the first or second feature, it is returned.
  • The IF statement adds a <there-is-more/> element to the result if there are more than two features in the product catalog.
  • Because not all product models have their catalog descriptions stored in the table, the WHERE clause is used to discard rows where CatalogDescriptions is NULL.

This is a partial result:

<Product ProductModelID="19" ProductModelName="Mountain 100">
  <p1:Warranty xmlns:p1="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelWarrAndMain">
    <p1:WarrantyPeriod>3 year</p1:WarrantyPeriod>
    <p1:Description>parts and labor</p1:Description>
  </p1:Warranty>
  <p2:Maintenance xmlns:p2="http://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelWarrAndMain">
    <p2:NoOfYears>10</p2:NoOfYears>
    <p2:Description>maintenance contact available through your dealer or
                    any AdventureWorks retail store.</p2:Description>
  </p2:Maintenance>
  <there-is-more/>
</Product> 
…

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