Re: patch: function xmltable

On 24 September 2016 at 14:01, Pavel Stehule <pavel.stehule@gmail.com> wrote:

>> Did some docs copy-editing and integrated some examples. Explained how
>> nested elements work, that multiple top level elements is an error,
>> etc. Explained the time-of-evaluation stuff. Pointed out that you can
>> refer to prior output columns in PATH and DEFAULT, since that's weird
>> and unusual compared to normal SQL. Documented handling of multiple
>> node matches, including the surprising results of somepath/text() on
>> <somepath>x<!--blah-->y</somepath>. Documented handling of nested
>> elements. Documented that xmltable works only on XML documents, not
>> fragments/forests.
>
>
> I don't understand to this sentence: "It is possible for a PATH expression
> to reference output columns that appear before it in the column-list, so
> paths may be dynamically constructed based on other parts of the XML
> document:"

This was based on a misunderstanding of something you said earlier. I
thought the idea was to allow this to work:

SELECT * FROM xmltable('/x' PASSING
'<x><elemName>a</elemName><a>value</a></x>' COLUMNS elemName text,
extractedValue text PATH elemName);

... but it doesn't:


SELECT * FROM xmltable('/x' PASSING
'<x><elemName>a</elemName><a>value</a></x>' COLUMNS elemName text,
extractedValue text PATH elemName);
ERROR:  column "elemname" does not exist
LINE 1: ...' COLUMNS elemName text, extractedValue text PATH elemName);

... so please delete that text. I thought I'd tested it but the state
of my tests dir says I just got distracted by another task at the
wrong time.

-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services