id Function (XQuery)

The following example uses fn:id to retrieve the <employee> elements, based on the IDREF manager attribute. In this example, the manager attribute is an IDREF type attribute and the eid attribute is an ID type attribute.

For a specific manager attribute value, the id() function finds the <employee> element whose ID type attribute value matches the input IDREF value. In other words, for a specific employee, the id() function returns employee manager.

This is what happens in the example:

• An XML schema collection is created.

• A typed xml variable is created by using the XML schema collection.

• The query retrieves the element that has an ID attribute value referenced by the manager IDREF attribute of the <employee> element.

-- If exists, drop the XML schema collection (SC).
-- drop xml schema collection SC
-- go

create xml schema collection SC as
'<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:e="emp" targetNamespace="emp">
            <element name="employees" type="e:EmployeesType"/>
            <complexType name="EmployeesType">
                 <sequence>
                      <element name="employee" type="e:EmployeeType" minOccurs="0" maxOccurs="unbounded" />
                 </sequence>
            </complexType>  
 
            <complexType name="EmployeeType">
                        <attribute name="eid" type="ID" />
                        <attribute name="name" type="string" />
                        <attribute name="manager" type="IDREF" />
            </complexType>       
</schema>'
go

declare @x xml(SC)
set @x='<e:employees xmlns:e="emp">
<employee eid="e1" name="Joe" manager="e10" />
<employee eid="e2" name="Bob" manager="e10" />
<employee eid="e10" name="Dave" manager="e10" />
</e:employees>'
 
select @x.value(' declare namespace e="emp"; 
 (fn:id(e:employees/employee[@name="Joe"]/@manager)/@name)[1]', 'varchar(50)') 
Go

The query returns "Dave" as the value. This indicates that Dave is Joe's manager.

In the following example, the OrderList attribute of the <Customer> element is an IDREFS type attribute. It lists the order ids for that specific customer. For each order id, there is an <Order> element child under the <Customer> providing the order value.

The query expression, data(CustOrders:Customers/Customer[1]/@OrderList)[1], retrieves the first value from the IDRES list for the first customer. This value is then passed to the id() function. The function then finds the <Order> element whose OrderID attribute value matches the input to the id() function.

drop xml schema collection SC
go
create xml schema collection SC as
'<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:Customers="Customers" targetNamespace="Customers">
            <element name="Customers" type="Customers:CustomersType"/>
            <complexType name="CustomersType">
                        <sequence>
                            <element name="Customer" type="Customers:CustomerType" minOccurs="0" maxOccurs="unbounded" />
                        </sequence>
            </complexType>
             <complexType name="OrderType">
                <sequence minOccurs="0" maxOccurs="unbounded">
                            <choice>
                                <element name="OrderValue" type="integer" minOccurs="0" maxOccurs="unbounded"/>
                            </choice>
                </sequence>                                           
                <attribute name="OrderID" type="ID" />
            </complexType>

            <complexType name="CustomerType">
                <sequence minOccurs="0" maxOccurs="unbounded">
                            <choice>
                                <element name="spouse" type="string" minOccurs="0" maxOccurs="unbounded"/>
                                <element name="Order" type="Customers:OrderType" minOccurs="0" maxOccurs="unbounded"/>
                            </choice>
                </sequence>                                           
                <attribute name="CustomerID" type="string" />
                <attribute name="OrderList" type="IDREFS" />
            </complexType>
 </schema>'
go
declare @x xml(SC)
set @x='<CustOrders:Customers xmlns:CustOrders="Customers">
                <Customer CustomerID="C1" OrderList="OrderA OrderB"  >
                              <spouse>Jenny</spouse>
                                <Order OrderID="OrderA"><OrderValue>11</OrderValue></Order>
                                <Order OrderID="OrderB"><OrderValue>22</OrderValue></Order>

                </Customer>
                <Customer CustomerID="C2" OrderList="OrderC OrderD" >
                                <spouse>John</spouse>
                                <Order OrderID="OrderC"><OrderValue>33</OrderValue></Order>
                                <Order OrderID="OrderD"><OrderValue>44</OrderValue></Order>

                        </Customer>
                <Customer CustomerID="C3"  OrderList="OrderE OrderF" >
                                <spouse>Jane</spouse>
                                <Order OrderID="OrderE"><OrderValue>55</OrderValue></Order>
                                <Order OrderID="OrderF"><OrderValue>55</OrderValue></Order>
                </Customer>
                <Customer CustomerID="C4"  OrderList="OrderG"  >
                                <spouse>Tim</spouse>
                                <Order OrderID="OrderG"><OrderValue>66</OrderValue></Order>
                        </Customer>
                <Customer CustomerID="C5"  >
                </Customer>
                <Customer CustomerID="C6" >
                </Customer>
                <Customer CustomerID="C7"  >
                </Customer>
</CustOrders:Customers>'
select @x.query('declare namespace CustOrders="Customers";
  id(data(CustOrders:Customers/Customer[1]/@OrderList)[1])')

-- result
<Order OrderID="OrderA">
  <OrderValue>11</OrderValue>
</Order>

These are the limitations:

• SQL Server does not support the two-argument version of id().

• SQL Server requires the argument type of id() to be a subtype of xs:IDREF*.