functions-on-sequences-empty.md

title	description	author	ms.author	ms.date	ms.service	ms.subservice	ms.topic	helpviewer_keywords	dev_langs
empty Function (XQuery)	Learn about the XQuery function empty() that returns a value indicating whether a specified sequence of items is empty.	rothja	jroth	03/09/2017	sql	xml	language-reference	empty function fn:empty function	XML

Functions on Sequences - empty

[!INCLUDE SQL Server Azure SQL Database]

Returns True if the value of $arg is an empty sequence. Otherwise, the function returns False.

Syntax

  
fn:empty($arg as item()*) as xs:boolean  

Arguments

$arg
A sequence of items. If the sequence is empty, the function returns True. Otherwise, the function returns False.

Remarks

The fn:exists() function is not supported. As an alternative, the not() function can be used.

Examples

This topic provides XQuery examples against XML instances that are stored in various xml type columns in the AdventureWorks database.

A. Using the empty() XQuery function to determine if an attribute is present

In the manufacturing process for Product Model 7, this query returns all the work center locations that do not have a MachineHours attribute.

SELECT ProductModelID, Instructions.query('  
declare namespace AWMI="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions";  
     for $i in /AWMI:root/AWMI:Location[empty(@MachineHours)]  
     return  
       <Location  
            LocationID="{ ($i/@LocationID) }"  
            LaborHrs="{ ($i/@LaborHours) }" >  
            {   
              $i/@MachineHours  
            }    
       </Location>  
') as Result  
FROM Production.ProductModel  
where ProductModelID=7  

This is the result:

ProductModelID      Result          
-------------- ------------------------------------------  
7              <Location LocationID="30" LaborHrs="1"/>  
               <Location LocationID="50" LaborHrs="3"/>  
               <Location LocationID="60" LaborHrs="4"/>  

The following, slightly modified, query returns "NotFound" if the MachineHour attribute is not present:

SELECT ProductModelID, Instructions.query('  
declare namespace p14="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelManuInstructions";  
     for $i in /p14:root/p14:Location  
     return  
       <Location  
            LocationID="{ ($i/@LocationID) }"  
            LaborHrs="{ ($i/@LaborHours) }" >  
            {   
                 if (empty($i/@MachineHours)) then  
                    attribute MachineHours { "NotFound" }  
                 else  
                    attribute MachineHours { data($i/@MachineHours) }  
            }    
       </Location>  
') as Result  
FROM Production.ProductModel  
where ProductModelID=7  

This is the result:

ProductModelID Result                         
-------------- -----------------------------------  
7                
  <Location LocationID="10" LaborHrs="2.5" MachineHours="3"/>  
  <Location LocationID="20" LaborHrs="1.75" MachineHours="2"/>  
  <Location LocationID="30" LaborHrs="1" MachineHours="NotFound"/>  
  <Location LocationID="45" LaborHrs="0.5" MachineHours="0.65"/>  
  <Location LocationID="50" LaborHrs="3" MachineHours="NotFound"/>  
  <Location LocationID="60" LaborHrs="4" MachineHours="NotFound"/>  

See Also

XQuery Functions against the xml Data Type
exist() Method (xml Data Type)