SELECT
 XMLConcat(XMLElement("first", q_tab.first_name), 
           XMLElement("last", q_tab.last_name))
     AS xml_out
FROM 
 (SELECT 'John' first_name, 'Doe' last_name FROM DUAL
  UNION
  SELECT 'Jane' first_name, 'Doe' last_name FROM DUAL
 ) q_tab;