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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.
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‎doc/src/sgml/func.sgml

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@@ -14655,6 +14655,60 @@ 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 <replaceable>document { $EXPR }</replaceable>. It replaces any
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document nodes in the input with their children and wraps the whole result in a
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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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Original file line numberDiff line numberDiff line change
@@ -625,7 +625,7 @@ 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
628-
X030 XMLDocument NO
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X030 XMLDocument YES
629629
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)
523523
}
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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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526544
Datum
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xmltext(PG_FUNCTION_ARGS)
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{

‎src/include/catalog/pg_proc.dat

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@@ -9143,6 +9143,9 @@
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{ oid => '3813', descr => 'generate XML text node',
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proname => 'xmltext', prorettype => 'xml', proargtypes => 'text',
91459145
prosrc => 'xmltext' },
9146+
{ oid => '3814', descr => 'generate XML document',
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proname => 'xmldocument', prorettype => 'xml', proargtypes => 'xml',
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prosrc => 'xmldocument'},
91469149

91479150
{ 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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@@ -1881,3 +1881,61 @@ 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
18821882
(1 row)
18831883

1884+
SELECT
1885+
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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1900+
SELECT xmldocument(NULL);
1901+
xmldocument
1902+
-------------
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(1 row)
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SELECT xmldocument('<foo>bar</foo>'::xml);
1907+
xmldocument
1908+
----------------
1909+
<foo>bar</foo>
1910+
(1 row)
1911+
1912+
SELECT xmldocument('foo'::xml);
1913+
xmldocument
1914+
-------------
1915+
foo
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(1 row)
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1918+
SELECT xmldocument('foo');
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xmldocument
1920+
-------------
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foo
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(1 row)
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1924+
SELECT xmldocument('');
1925+
xmldocument
1926+
-------------
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(1 row)
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SELECT xmldocument(' ');
1931+
xmldocument
1932+
-------------
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1934+
(1 row)
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1936+
SELECT xmldocument(xmlcomment('comment'));
1937+
xmldocument
1938+
----------------
1939+
<!--comment-->
1940+
(1 row)
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‎src/test/regress/expected/xml_1.out

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@@ -1496,3 +1496,50 @@ ERROR: unsupported XML feature
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LINE 1: SELECT xmltext('x'|| '<P>73</P>'::xml || .42 || true || 'j':...
14971497
^
14981498
DETAIL: This functionality requires the server to be built with libxml support.
1499+
SELECT
1500+
xmldocument(
1501+
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('<"&>'))
1508+
)
1509+
);
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ERROR: unsupported XML feature
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DETAIL: This functionality requires the server to be built with libxml support.
1512+
SELECT xmldocument(NULL);
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xmldocument
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-------------
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1516+
(1 row)
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SELECT xmldocument('<foo>bar</foo>'::xml);
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ERROR: unsupported XML feature
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LINE 1: SELECT xmldocument('<foo>bar</foo>'::xml);
1521+
^
1522+
DETAIL: This functionality requires the server to be built with libxml support.
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SELECT xmldocument('foo'::xml);
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ERROR: unsupported XML feature
1525+
LINE 1: SELECT xmldocument('foo'::xml);
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^
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DETAIL: This functionality requires the server to be built with libxml support.
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SELECT xmldocument('foo');
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ERROR: unsupported XML feature
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LINE 1: SELECT xmldocument('foo');
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^
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DETAIL: This functionality requires the server to be built with libxml support.
1533+
SELECT xmldocument('');
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ERROR: unsupported XML feature
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LINE 1: SELECT xmldocument('');
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^
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DETAIL: This functionality requires the server to be built with libxml support.
1538+
SELECT xmldocument(' ');
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ERROR: unsupported XML feature
1540+
LINE 1: SELECT xmldocument(' ');
1541+
^
1542+
DETAIL: This functionality requires the server to be built with libxml support.
1543+
SELECT xmldocument(xmlcomment('comment'));
1544+
ERROR: unsupported XML feature
1545+
DETAIL: This functionality requires the server to be built with libxml support.

‎src/test/regress/expected/xml_2.out

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@@ -1867,3 +1867,61 @@ 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
18681868
(1 row)
18691869

1870+
SELECT
1871+
xmldocument(
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xmlelement(NAME root,
1873+
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('<"&>'))
1879+
)
1880+
);
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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>
1884+
(1 row)
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SELECT xmldocument(NULL);
1887+
xmldocument
1888+
-------------
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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
1912+
-------------
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1914+
(1 row)
1915+
1916+
SELECT xmldocument(' ');
1917+
xmldocument
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-------------
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(1 row)
1921+
1922+
SELECT xmldocument(xmlcomment('comment'));
1923+
xmldocument
1924+
----------------
1925+
<!--comment-->
1926+
(1 row)
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‎src/test/regress/sql/xml.sql

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Original file line numberDiff line numberDiff line change
@@ -679,3 +679,22 @@ SELECT xmltext(' ');
679679
SELECT xmltext('foo `$_-+?=*^%!|/\()[]{}');
680680
SELECT xmltext('foo & <"bar">');
681681
SELECT xmltext('x'|| '<P>73</P>'::xml || .42 || true || 'j'::char);
682+
683+
SELECT
684+
xmldocument(
685+
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>'),
689+
xmlelement(NAME bar, xmlconcat('va', 'lue')),
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xmlpi(name pi),
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xmlelement(NAME txt, xmltext('<"&>'))
692+
)
693+
);
694+
SELECT xmldocument(NULL);
695+
SELECT xmldocument('<foo>bar</foo>'::xml);
696+
SELECT xmldocument('foo'::xml);
697+
SELECT xmldocument('foo');
698+
SELECT xmldocument('');
699+
SELECT xmldocument(' ');
700+
SELECT xmldocument(xmlcomment('comment'));

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