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boolean-constructor-functions-true-xquery.md

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title true Function (XQuery) | Microsoft Docs
ms.custom
ms.date 08/10/2016
ms.prod sql
ms.prod_service sql
ms.reviewer
ms.technology xml
ms.topic language-reference
dev_langs
XML
helpviewer_keywords
fn:true function
true function
ms.assetid 318e370d-0444-4812-afe4-307df7ef9f3b
author rothja
ms.author jroth

Boolean Constructor Functions - true (XQuery)

[!INCLUDEtsql-appliesto-ss2008-xxxx-xxxx-xxx-md]

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

Syntax

fn:true() as xs:boolean

Examples

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

See Also

Boolean Constructor Functions (XQuery)