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Add XMLDocument function (SQL/XML X030)
This patch adds the SQL/XML X030 function XMLDocument. It returns an XML document from a given XML expression. An XML document node can have any number of children nodes. Since our XML data type corresponds to XML(CONTENT(ANY)), any expression already validated by the input function is considered valid output for XMLDocument. As a result, this function simply returns its input value. While this implementation is quite trivial, it follows the SQL/XML standard and facilitates the migration of SQL statements from other database systems that also support X030. Usage: WITH t(x) AS ( VALUES (xmlparse(DOCUMENT '<root><foo>bar</foo></root>')), (xmlforest(42 AS foo, 73 AS bar)), (NULL) ) SELECT xmldocument(x) FROM t; xmldocument ----------------------------- <root><foo>bar</foo></root> <foo>42</foo><bar>73</bar> (3 rows) This patch also adds documentation and tests. Author: Jim Jones <jim.jones@uni-muenster.de> Reviewed-by: Chapman Flack <jcflack@acm.org> Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com> Reviewed-by: Robert Treat <rob@xzilla.net> Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
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‎doc/src/sgml/func/func-xml.sgml‎

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@@ -93,6 +93,60 @@ SELECT xmlcomment('hello');
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</para>
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</sect3>
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<sect3 id="functions-producing-xml-xmldocument">
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<title><literal>xmldocument</literal></title>
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<indexterm>
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<primary>xmldocument</primary>
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</indexterm>
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<synopsis>
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<function>xmldocument</function> ( <type>xml</type> ) <returnvalue>xml</returnvalue>
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</synopsis>
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<para>
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The <function>xmldocument</function> function returns the input argument
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unchanged, or <literal>NULL</literal> if the argument is <literal>NULL</literal>,
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and is provided for compatibility.
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The SQL-standard <replaceable>XMLDocument</replaceable> function applied to an
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XML value <literal>$EXPR</literal>, has effects equivalent to the XML
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Query expression <literal>document { <replaceable>$EXPR</replaceable> }</literal>.
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It replaces any document nodes in the input with their children and wraps the whole
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result in a single <replaceable>document node</replaceable>.
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In the XML Query standard, a <replaceable>document node</replaceable> represents
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a relaxed version of an XML document structure. This corresponds to what PostgreSQL's
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single XML type allows, meaning that any valid non-null PostgreSQL XML value can be
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returned unchanged. Other systems may support more permissive XML data types,
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such as <literal>XML(SEQUENCE)</literal>, which allow values that do not conform to
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this structure. In PostgreSQL, every valid non-null value of the XML type already has
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that structure, making additional processing by this function unnecessary.
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</para>
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<para>
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Example:
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<screen><![CDATA[
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WITH xmldata (val) AS (
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VALUES
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(xmlparse(DOCUMENT '<root><foo>bar</foo></root>')),
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(xmltext('foo&bar')),
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(xmlelement(NAME el)),
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(xmlforest(42 AS foo, 73 AS bar))
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)
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SELECT xmldocument(val) FROM xmldata;
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xmldocument
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-----------------------------
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<root><foo>bar</foo></root>
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foo&amp;bar
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<el/>
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<foo>42</foo><bar>73</bar>
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(4 rows)
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]]></screen>
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</para>
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</sect3>
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<sect3 id="functions-producing-xml-xmlconcat">
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<title><literal>xmlconcat</literal></title>
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‎src/backend/catalog/sql_features.txt‎

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@@ -725,7 +725,7 @@ X015 Fields of XML type NO
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X016 Persistent XML values YES
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X020 XMLConcat YES
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X025 XMLCast NO
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X030 XMLDocument NO
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X030 XMLDocument YES supported except for RETURNING
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X031 XMLElement YES
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X032 XMLForest YES
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X034 XMLAgg YES

‎src/backend/utils/adt/xml.c‎

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@@ -523,6 +523,24 @@ xmlcomment(PG_FUNCTION_ARGS)
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}
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/*
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* xmldocument implements the SQL/XML function XMLDocument (X030).
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* Since our XML data type corresponds to XML(CONTENT(ANY)), any
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* expression already validated by the input function is considered
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* valid output for XMLDocument. As a result, this function simply
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* returns its input value.
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*/
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Datum
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xmldocument(PG_FUNCTION_ARGS)
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{
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#ifdef USE_LIBXML
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PG_RETURN_DATUM(PG_GETARG_DATUM(0));
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#else
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NO_XML_SUPPORT();
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return 0;
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#endif /* not USE_LIBXML */
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}
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Datum
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xmltext(PG_FUNCTION_ARGS)
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{

‎src/include/catalog/pg_proc.dat‎

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{ oid => '3813', descr => 'generate XML text node',
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proname => 'xmltext', prorettype => 'xml', proargtypes => 'text',
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prosrc => 'xmltext' },
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{ oid => '3814', descr => 'generate XML document',
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proname => 'xmldocument', prorettype => 'xml', proargtypes => 'xml',
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prosrc => 'xmldocument' },
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{ oid => '2923', descr => 'map table contents to XML',
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proname => 'table_to_xml', procost => '100', provolatile => 's',

‎src/test/regress/expected/xml.out‎

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@@ -1891,3 +1891,61 @@ SELECT xmltext('x'|| '<P>73</P>'::xml || .42 || true || 'j'::char);
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x&lt;P&gt;73&lt;/P&gt;0.42truej
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(1 row)
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SELECT
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xmldocument(
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xmlelement(NAME root,
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xmlattributes(42 AS att),
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xmlcomment('comment'),
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xmlelement(NAME foo,'<foo&bar>'),
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xmlelement(NAME bar, xmlconcat('va', 'lue')),
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xmlpi(name pi),
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xmlelement(NAME txt, xmltext('<"&>'))
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)
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);
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xmldocument
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------------------------------------------------------------------------------------------------------------------------
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<root att="42"><!--comment--><foo>&lt;foo&amp;bar&gt;</foo><bar>value</bar><?pi?><txt>&lt;&quot;&amp;&gt;</txt></root>
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(1 row)
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SELECT xmldocument(NULL);
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xmldocument
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-------------
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(1 row)
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SELECT xmldocument('<foo>bar</foo>'::xml);
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xmldocument
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----------------
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<foo>bar</foo>
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(1 row)
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SELECT xmldocument('foo'::xml);
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xmldocument
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-------------
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foo
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(1 row)
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SELECT xmldocument('foo');
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xmldocument
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-------------
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foo
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(1 row)
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SELECT xmldocument('');
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xmldocument
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-------------
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(1 row)
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SELECT xmldocument(' ');
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xmldocument
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-------------
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(1 row)
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SELECT xmldocument(xmlcomment('comment'));
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xmldocument
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----------------
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<!--comment-->
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(1 row)
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‎src/test/regress/sql/xml.sql‎

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@@ -685,3 +685,22 @@ SELECT xmltext(' ');
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SELECT xmltext('foo `$_-+?=*^%!|/\()[]{}');
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SELECT xmltext('foo & <"bar">');
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SELECT xmltext('x'|| '<P>73</P>'::xml || .42 || true || 'j'::char);
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SELECT
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xmldocument(
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xmlelement(NAME root,
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xmlattributes(42 AS att),
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xmlcomment('comment'),
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xmlelement(NAME foo,'<foo&bar>'),
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xmlelement(NAME bar, xmlconcat('va', 'lue')),
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xmlpi(name pi),
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xmlelement(NAME txt, xmltext('<"&>'))
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)
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);
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SELECT xmldocument(NULL);
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SELECT xmldocument('<foo>bar</foo>'::xml);
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SELECT xmldocument('foo'::xml);
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SELECT xmldocument('foo');
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SELECT xmldocument('');
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SELECT xmldocument(' ');
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SELECT xmldocument(xmlcomment('comment'));

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