我正在尝试在Oracle中创建一个XML文档。它应该在顶层有一个序列值，还有一些行级项目。例如，查询在没有行项目的情况下工作

WITH j AS (
  SELECT
    'abc' test
  FROM
    dual
  GROUP BY
    1
)
SELECT
  XMLSERIALIZE(DOCUMENT XMLELEMENT(
    "WhseSnapshot",
    XMLELEMENT(
      "mdDC",
      MD_EXTRACT_ID_SEQ.NEXTVAL
    )
  ))
FROM
  j;

产生输出

<WhseSnapshot><mdDC>157</mdDC></WhseSnapshot>

向查询添加行项目，如下所示

WITH j AS (
  SELECT
    'abc' test
  FROM
    dual
  GROUP BY
    1
)
SELECT
  XMLSERIALIZE(DOCUMENT XMLELEMENT(
    "WhseSnapshot",
    XMLELEMENT(
      "mdDC",
      MD_EXTRACT_ID_SEQ.NEXTVAL
    ),
    XMLAGG(XMLELEMENT(
      "line",
           XMLFOREST(j.test AS "test")
    ))
  ))
FROM
  j;

导致以下错误

ORA-02287: sequence number not allowed here
02287. 00000 -  "sequence number not allowed here"
*Cause:    The specified sequence number (CURRVAL or NEXTVAL) is inappropriate
           here in the statement.
*Action:   Remove the sequence number.
Error at Line: 84 Column: 25

有没有人能达到类似的目标？我希望避免PL/SQL块或函数，并尽可能坚持使用常规SQL。