使用Oracle PL/SQL XMLQUERY和XQuery而不是“提取（XML）”有什么优势

我注意到Oracle 11g中不推荐使用Oracle EXTRACTXML函数

我曾经通过以下方法进行XML处理：

DECLARE
  TYPE xmltype_table IS TABLE OF xmltype INDEX BY PLS_INTEGER;
  vt_xml_tab xmltype_table;
  v_xml      xmltype;
BEGIN
  --Generate simple XML document to pretend we received it by some interface
  SELECT xmltype(dbms_xmlgen.getxml('select level, dbms_random.random rnd from dual connect by level<1000')) INTO v_xml FROM dual;

  --Get nodes
  SELECT VALUE(xm) xmlt BULK COLLECT INTO vt_xml_tab FROM TABLE(xmlsequence(v_xml.extract('/ROWSET/ROW/LEVEL'))) xm;

  --Do whatever processing I like
  FOR i IN 1..vt_xml_tab.count LOOP
    dbms_output.put_line(vt_xml_tab(i).extract('LEVEL/text()').getstringval());
  END LOOP;
END;
/

由于EXTRACT已被弃用，Oracle建议我使用XMLQUERY：

我想将我之前的处理重写如下：

DECLARE
  TYPE xmltype_table IS TABLE OF xmltype INDEX BY PLS_INTEGER;
  vt_xml_tab xmltype_table;
  v_xml      xmltype;
BEGIN
  --Generate simple XML document to pretend we received it by some interface
  SELECT xmltype(dbms_xmlgen.getxml('select level, dbms_random.random rnd from dual connect by level<1000'))
    INTO v_xml
    FROM dual;

  SELECT xmlquery('for $i in /ROWSET/ROW
      return $i/LEVEL' passing rowset_xml RETURNING content)
    INTO v_xml
    FROM (SELECT v_xml rowset_xml FROM dual);

  --Get nodes
  SELECT VALUE(xm) xmlt BULK COLLECT INTO vt_xml_tab FROM TABLE(xmlsequence(v_xml)) xm;

  --Do whatever processing I like
  FOR i IN 1 .. vt_xml_tab.count LOOP
    FOR x IN (SELECT extractvalue(vt_xml_tab(i), 'LEVEL') lvl FROM dual) LOOP
      dbms_output.put_line(x.lvl);
    END LOOP;
  END LOOP;
END;
/

但事实证明，在我用挂钟测量的机器上，使用XMLQUERY要慢0.8秒而不是1.8秒

有没有更好的方法不使用提取函数