How to do an update with XML column ? - Mailing list pgsql-general

select id, unnest(xpath(        '//cit:CI_Organisation/cit:name/gco:CharacterString/text()',       CAST(data AS XML),        ARRAY[            ARRAY['cit', 'http://standards.iso.org/iso/19115/-3/cit/2.0'],            ARRAY['gco', 'http://standards.iso.org/iso/19115/-3/gco/1.0'],            ARRAY['mdb','http://standards.iso.org/iso/19115/-3/mdb/2.0'],            ARRAY['cat','http://standards.iso.org/iso/19115/-3/cat/1.0'],        ])) as orga_name, changedate, createdate, displayorder, doctype, extra, popularity, rating, root, schemaid, title, istemplate, isharvested, harvesturi,       harvestuuid, groupowner, metadata.owner, metadata.source, uuid
from public.metadata
group by orga_name

I obtained : 

ERROR:  could not identify an equality operator for type xml
LINE 39: group by orga_name                  ^ 

SQL state: 42883
Character: 2556

Thanks so much