oracle把查询结果以逗号拼接

1.这种是后面有逗号的
select xmlagg(xmlparse(content files || ','wellformed) order by files).getclobval() as files from
(select field008 as files from ufp2h3p81666516120213
union all
select field002 as files from ufq9k2s21700208561930)

2.后面没有逗号

SELECT LISTAGG(files, ',') WITHIN GROUP (ORDER BY files ASC) AS files FROM (select field008 as files from ufp2h3p81666516120213
union all
select field002 as files from ufq9k2s21700208561930)