ORA-19100:应传递或返回关键字

我有一个包含XML数据的简单表

create table emp
(dept xmltype)

以及其中的数据

insert into emp values ('<dept bldg="101">
<employee id="901">
    <name>
        <first>John</first>
        <last>Doe</last>
    </name>
    <office>344</office>
    <salary currency="USD">55000</salary>
</employee>
</dept>')


insert into emp values ('<dept bldg="103">
<employee id="902">
    <name>
        <first>Peter</first>
        <last>Pan</last>
    </name>
    <office>216</office>
    <phone>905-416-5004</phone>
    </employee>
</dept>')



insert into emp values ('<dept bldg="114">
<employee id="903">
    <name>
        <first>Mary</first>
        <last>Jones</last>
    </name>
    <office>415</office>
    <phone>905-403-6112</phone>
    <phone>647-504-4546</phone>
    <salary currency="USD">64000</salary>
</employee>
</dept>')

当我执行以下操作时,它抛出ORA-19100:传递或返回关键字

select XMLCAST(XMLQUERY('$INPT_XML/dept/employee/office/text()' PASSING dept  
AS "INPT_XML") AS VARCHAR(20))
FROM emp;

有人能帮我回答这个问题吗?