从PostgreSQL版本9开始，只需使用 string_agg ：

Since PostgreSQL version 9, this is done simply by using string_agg:

SELECT
  cmsdocument.internaldocid,
  cmsdocument.documentid,
  cmsdocument.versionid,
  cmsdocversion.title,
  string_agg(cmstag.tagname, ',')
FROM 
  public.cmsobjecttag,
  public.cmstag,
  public.cmsdocument,
  public.cmsdocversion,
  public.cmsuser
WHERE 
  cmsobjecttag.tagid = cmstag.tagid AND
  cmsobjecttag.objectid = cmsdocument.internaldocid AND
  cmsdocument.internaldocid = cmsdocversion.internaldocid AND
  cmsdocument.userid = cmsuser.userid AND
  cmsdocversion.state = 'published' AND
  cmsobjecttag.objecttype = '102'
GROUP BY 
  cmsdocument.internaldocid,
  cmsdocument.documentid,
  cmsdocument.versionid,
  cmsdocversion.title