Re: PostgreSQL vs SQL/XML Standards

From: Markus Winand <markus(dot)winand(at)winand(dot)at>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Chapman Flack <chap(at)anastigmatix(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: PostgreSQL vs SQL/XML Standards
Date: 2018-11-08 14:18:26
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> On 2018-11-6, at 15:23 , Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> po 29. 10. 2018 v 11:45 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> napsal:
> po 29. 10. 2018 v 10:11 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> napsal:
> Hi
> čt 25. 10. 2018 v 21:47 odesílatel Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> napsal:
> On 2018-Oct-25, Pavel Stehule wrote:
> > I am thinking so I can fix some issues related to XMLTABLE. Please, send me
> > more examples and test cases.
> Please see Markus Winand's patch that I referenced upthread.
> here is a fix of some XMLTABLE mentioned issues.
> this update allows cast boolean to numeric types from XPath expressions
> Attached patch solves some cast issues mentioned by Chap. It solves issue reported by Markus. I didn't use Markus's code, but it was inspiration for me. I found native solution from libxml2.
> Regards
> Pavel

Better than my patch.

But I think the chunk in xml_xmlnodetoxmltype of my patch is still needed — in one way or the other (see below).

# select * from xmltable('*' PASSING '<e>pre<!--c1--><?pi arg?><![CDATA[&ent1]]><n2>&amp;deep</n2>post</e>' COLUMNS x XML PATH 'node()');
(1 row)

Output is not the original XML.

I dug a little further and found another case that doesn’t looks right even with my change to xml_xmlnodetoxmltype applied:

# select * from xmltable('*' PASSING '<e>pre<!--c1--><?pi arg?><![CDATA[&ent1]]><n2>&amp;deep</n2>post</e>' COLUMNS x XML PATH '/');
(1 row)

Oracle gives in both cases XML.

To fix that I included XML_DOCUMENT_NODE in the list of nodes that use xmlNodeDump. Now I wonder if that logic should be reversed to use the xmlXPathCastNodeToString branch in a few selected cases but default to the branch xmlNodeDump for all other cases?

I guess those few cases might be XML_ATTRIBUTE_NODE and XML_TEXT_NODE. Regression tests are happy with that approach but I don’t think that proves a lot.


diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 37d85f7..7c1f884 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -3682,7 +3682,7 @@ xml_xmlnodetoxmltype(xmlNodePtr cur, PgXmlErrorContext *xmlerrcxt)
xmltype *result;

- if (cur->type == XML_ELEMENT_NODE)
+ if (cur->type != XML_ATTRIBUTE_NODE && cur->type != XML_TEXT_NODE)
xmlBufferPtr buf;
xmlNodePtr cur_copy;

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