Re: XMLDocument (SQL/XML X030)

On 24.01.25 22:01, Chapman Flack wrote:
> It seems to me the key connection there is that the ISO SQL standard
> defines XMLDOCUMENT by equivalence to what `document { $expr }` means
> in the W3 XML Query standard.


It seems I missed one sentence. My bad.

Next try... :)


The <function>xmldocument</function> function returns the input argument
unchanged, or <literal>NULL</literal> if the argument is
<literal>NULL</literal>, and is provided for compatibility.

The SQL-standard <replaceable>XMLDocument</replaceable> function applied
to an XML value <literal>$EXPR</literal>, has effects equivalent to the
XML Query expression <replaceable>document { $EXPR }</replaceable>. It
replaces any document nodes in the input with their children and wraps
the whole result in a single <replaceable>document node</replaceable>.

In the XML Query standard, a <replaceable>document node</replaceable>
represents a relaxed version of an XML document structure. This
corresponds to what PostgreSQL's single XML type allows, meaning that
any valid non-null PostgreSQL XML value can be returned unchanged. Other
systems may support more permissive XML data types, such as
<literal>XML(SEQUENCE)</literal>, which allow values that do not conform
to this structure. In PostgreSQL, every valid non-null value of the XML
type already has that structure, making additional processing by this
function unnecessary.

v6 attached.

Thanks.

Best regards, Jim