Utilizzo di xpath per estrarre i dati da una colonna XML in postgres

Funziona:

WITH tbl(p_xml) AS (  -- CTE just to provide test table with xml value
   SELECT '<promotions xmlns="http://www.demandware.com/xml/impex/promotion/2008-01-31">
              <campaign campaign-id="2013-1st-semester-jet-giveaways">
                 <description>2013 1st Semester Jet Giveaways</description>
                 <enabled-flag>true</enabled-flag>
                 <start-date>2013-01-01T05:00:00.000Z</start-date>
                 <end-date>2013-07-01T04:00:00.000Z</end-date>
                 <customer-groups>
                    <customer-group group-id="Everyone"/>
                 </customer-groups>
              </campaign>
           </promotions>'::xml
    )  -- end of CTE, the rest is the solution
SELECT xpath('/n:promotions/n:campaign/n:description/text()', p_xml
           , '{{n,http://www.demandware.com/xml/impex/promotion/2008-01-31}}')
FROM   tbl;

Resi:

{"2013 1st Semester Jet Giveaways"}

Nota come assegno l'alias namespace n per il tuo spazio dei nomi nel terzo argomento di xpath() e usalo a tutti i livelli di xpath.

Se rimuovi lo spazio dei nomi XML dal documento, tutto diventa molto più semplice:

WITH tbl(p_xml) AS (  -- not the missing namespace below
   SELECT '<promotions>
              <campaign campaign-id="2013-1st-semester-jet-giveaways">
                 <description>2013 1st Semester Jet Giveaways</description>
                 <enabled-flag>true</enabled-flag>
                 <start-date>2013-01-01T05:00:00.000Z</start-date>
                 <end-date>2013-07-01T04:00:00.000Z</end-date>
                 <customer-groups>
                    <customer-group group-id="Everyone"/>
                 </customer-groups>
              </campaign>
           </promotions>'::xml
   )
SELECT xpath('/promotions/campaign/description/text()', p_xml)
FROM   tbl;

<rant> Sono solo io o sono tutti contenti di json e jsonb , quindi non dobbiamo occuparci di XML.</rant>