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Add XMLText function (SQL/XML X038)

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This function implements the standard XMLTest function, which
converts text into xml text nodes. It uses the libxml2 function
xmlEncodeSpecialChars to escape predefined entities (&"<>), so
that those do not cause any conflict when concatenating the text
node output with existing xml documents.

This also adds a note in  features.sgml about not supporting
XML(SEQUENCE). The SQL specification defines a RETURNING clause
to a set of XML functions, where RETURNING CONTENT or RETURNING
SEQUENCE can be defined. Since PostgreSQL doesn't support
XML(SEQUENCE) all of these functions operate with an
implicit RETURNING CONTENT.

Author: Jim Jones <jim.jones@uni-muenster.de>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Discussion: https://postgr.es/m/86617a66-ec95-581f-8d54-08059cca8885@uni-muenster.de
This commit is contained in:
Daniel Gustafsson
2023-11-06 09:38:29 +01:00
parent 7b5275eec3
commit 526fe0d799
9 changed files with 167 additions and 1 deletions
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9
doc/src/sgml/features.sgml
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@ -199,6 +199,15 @@
standard.
</para>
</listitem>
<listitem>
<para>
<productname>PostgreSQL</productname> does not support the
<literal>RETURNING CONTENT</literal> or <literal>RETURNING SEQUENCE</literal>
clauses, functions which are defined to have these in the specification
are implicitly returning content.
</para>
</listitem>
</itemizedlist>
</para>

30
doc/src/sgml/func.sgml
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@ -14180,6 +14180,36 @@ CREATE TYPE rainbow AS ENUM ('red', 'orange', 'yellow', 'green', 'blue', 'purple
documents for processing in client applications.
</para>
<sect3 id="functions-producing-xml-xmltext">
<title><literal>xmltext</literal></title>
<indexterm>
<primary>xmltext</primary>
</indexterm>
<synopsis>
<function>xmltext</function> ( <type>text</type> ) <returnvalue>xml</returnvalue>
</synopsis>
<para>
The function <function>xmltext</function> returns an XML value with a single
text node containing the input argument as its content. Predefined entities
like ampersand (<literal><![CDATA[&]]></literal>), left and right angle brackets
(<literal><![CDATA[< >]]></literal>), and quotation marks (<literal><![CDATA[""]]></literal>)
are escaped.
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmltext('< foo & bar >');
xmltext
-------------------------
&lt; foo &amp; bar &gt;
]]></screen>
</para>
</sect3>
<sect3 id="functions-producing-xml-xmlcomment">
<title><literal>xmlcomment</literal></title>