Functions on Sequences - empty

Artikkeli
04/03/2023

Applies to: SQL Server

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