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true Function (XQuery)

Returns the xs:boolean value True. This is equivalent to xs:boolean("1").

fn:true() as xs:boolean

This topic provides XQuery examples against XML instances that are stored in various xml type columns in the AdventureWorks2008R2 database. For an overview of each of these columns, see xml Data Type Representation in the AdventureWorks2008R2 Database.

A. Using the true() XQuery Boolean function

The following example queries an untyped xml variable. The expression in the value() method returns Boolean true() if "aaa" is the attribute value. The value() method of the xml data type converts the Boolean value into a bit and returns it.

DECLARE @x XML;
SET @x= '<ROOT><elem attr="aaa">bbb</elem></ROOT>'
select @x.value(' if ( (/ROOT/elem/@attr)[1] eq "aaa" ) then fn:true() else fn:false() ', 'bit');
go
-- result = 1

In the following example, the query is specified against a typed xml column. The if expression checks the typed Boolean value of the <ROOT> element and returns the constructed XML, accordingly. The example performs the following:

  • Creates an XML schema collection that defines the <ROOT> element of the xs:boolean type.

  • Creates a table with a typed xml column by using the XML schema collection.

  • Saves an XML instance in the column and queries it.

-- Drop table if exist
--DROP TABLE T
--go
DROP XML SCHEMA COLLECTION SC;
go
CREATE XML SCHEMA COLLECTION SC AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema"
targetNamespace="QNameXSD" >
      <element name="ROOT" type="boolean" nillable="true"/>
</schema>';
go
CREATE TABLE T (xmlCol XML(SC));
go
-- following OK
insert into T values ('<ROOT xmlns="QNameXSD">true</ROOT>');
 go
-- Retrieve the local name. 
SELECT xmlCol.query('declare namespace a="QNameXSD"; 
   if (/a:ROOT[1] eq true()) then
       <result>Found boolean true</result>
   else
       <result>Found boolean false</result>')

FROM T;
-- result = <result>Found boolean true</result>
-- Clean up
DROP TABLE T;
go
DROP XML SCHEMA COLLECTION SC;
go

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