How to group similar values using XQuery

Question

I have a table Employee with following columns
EmpNo number,
Title varchar2(100),
First_Name varchar2(100),
Last_Name varchar2(100),
1, Miss, A, B (Sample record in Employee Table)
There is an audit table Employee_A with columns
ID number (PK),
EmpNo number,
Field_Name varchar2(100),
Old_Value varchar2(100),
New_Value varchar2(100)
An update statement causes the Title of EmpNo=1 to change from Miss to Mrs and Last_Name from B to C. Hence the audit table has two records
1,1,Title, Miss,Mrs
2,1,Last_Name, B, C
I need to generate an xml which is as follows:
<Tag>
<Operation>Update</Operation>
<Key>1</Key>
<Data>
<Field>
<Column>Title</Column>
<NewValue>Mrs</NewValue>
</Field>
<Field>
<Column>Last_Name</Column>
<NewValue>C</NewValue>
</Field>
<Data>
</Tag>
How can we do this using XQuery?
If not, can we do this using xmlelement, xmlagg?

Answer 1

I tried the following:
SELECT XMLQuery('<Dummy>
{for $c in ora:view("Employee"),
           $ca in ora:view("Employee_A")
       let $emp := $c/ROW/EMPNO/text(),
           $emp_a := $ca/ROW/EMPNO/text(),
           $field := $ca/ROW/FIELD_NAME/text(),
           $new := $ca/ROW/NEW_VALUE/text()
           where $emp = $emp_a
       return
       <Tag>
         <operation>Update</operation>
         <key_id>$emp_a</key_id>
         <Data>
         <Field>
           <Column>{$field}</ent_id>
<NewValue>{$new}</NewValue>
</Field>
</Data>
</Tag>
}</Dummy' RETURNING CONTENT)
FROM dual;
The output that I'm getting is
<Dummy
<Tag>
<Operation>Update</Operation>
<Key>1</Key>
<Data>
<Field>
<Column>Title</Column>
<NewValue>Mrs</NewValue>
</Field>
<Data>
</Tag>
<Tag>
<Operation>Update</Operation>
<Key>1</Key>
<Data>
<Field>
<Column>Last_Name</Column>
<NewValue>C</NewValue>
</Field>
<Data>
</Tag>
</Dummy>
Two <Tag></Tag> gets created - one for each update entry. Please help