sql - 如何使用 PostgreSQL 将多行合并为一列？

Question

如何将多个结果合并到一列中？

例如，我的查询显示这个结果:

internaldocid | document id | versionid | title | tagname
1146 | DOC-1146 | 2 | Press Release | tag1
1146 | DOC-1146 | 2 | Press Release | tag2
1146 | DOC-1146 | 2 | Press Release | tag3

我希望它显示这个结果:

internaldocid | document id | versionid | title | tagname
1146 | DOC-1146 | 2 | Press Release | tag1, tag2, tag3

这是我的 SQL:

SELECT
  cmsdocument.internaldocid,
  cmsdocument.documentid,
  cmsdocument.versionid,
  cmsdocversion.title,
  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';

如有任何帮助，我们将不胜感激。

Answer 1

从 PostgreSQL 版本 9 开始，只需使用 string_agg 即可完成此操作:

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