Horton

Re: PostgreSQL vs SQL/XML Standards

Chapman Flack <chap@anastigmatix.net>

View thread View on postgr.es
From: Chapman Flack <chap@anastigmatix.net>
To: pgsql-hackers@lists.postgresql.org
Date: 2019-01-20T05:06:06Z
Lists: pgsql-hackers 
On 01/19/19 23:49, Pavel Stehule wrote:

> If I remember, described functionality was implemented in early patches,
> but was removed to simplify code. To now, there was not a request to do it.
> 
> Unfortunately, the documentation was not fixed.

I'll do that, as I'm working in there anyway. :)

> column expressions are evaluated once per row, but XPath  expression is
> compiled per row too, if I remember well.

I looked for evidence of that in the code, but did not find it; the
compilation appears to happen in XmlTableSetColumnFilter, which is
called from tfuncInitialize.

I can't guarantee I didn't miss something, though.

> We designed it more tolerant as
> we expected possibility to store XPath expression in one column and data in
> second column.

Perhaps if I could see an example showing the functionality... The nearest
I could find in the regression tests was the test with
 COLUMNS a int PATH '' || lower(_path) || 'c'
but, again, I think that test only demonstrates how LATERAL works, not
any behavior specific to xmltable.

Regards,
-Chap

Commits

  1. Improve documentation about our XML functionality

  2. Improve documentation about our XML functionality.

  3. Add volatile qualifier missed in commit 2e616dee9.

  4. Fix crash with old libxml2

  5. Fix minor deficiencies in XMLTABLE, xpath(), xmlexists()

  6. Fix the BY {REF,VALUE} clause of XMLEXISTS/XMLTABLE

  7. doc: Update README.links

  8. XPath fixes: