XPath query into hierarchical data, preserving ancestor–descendant relationship

Question

How can I express to PostgreSQL that I want values simultaneously from several hierarchical levels in an XPath query?

I have a document (in a PostgreSQL

Answer 1

Try this:

SELECT (xpath('./@name', parrot.node))[1] AS name
     , unnest(xpath('./descriptor/text()', parrot.node)) AS descriptor
FROM  (             
   SELECT unnest(xpath('./parrot', parrot_xml.document)) AS node
   FROM   parrot_xml
   ) parrot;

Produces exactly the requested output.

First, in the subquery, I retrieve whole parrot-nodes. One node per row.

Next, I get the name and the descriptors with xpath(). Both are arrays. I take the first (and only) element of name and split the descriptor array with `unnest(), thereby arriving at the desired result.

I wrote a comprehensive answer to a related question recently. May be of interest to you.