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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.15. XML Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="functions-uuid.html" title="9.14. UUID Functions" /><link rel="next" href="functions-json.html" title="9.16. JSON Functions and Operators" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.15. XML Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-uuid.html" title="9.14. UUID Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-json.html" title="9.16. JSON Functions and Operators">Next</a></td></tr></table><hr /></div><div class="sect1" id="FUNCTIONS-XML"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.15. XML Functions <a href="#FUNCTIONS-XML" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-xml.html#FUNCTIONS-PRODUCING-XML">9.15.1. Producing XML Content</a></span></dt><dt><span class="sect2"><a href="functions-xml.html#FUNCTIONS-XML-PREDICATES">9.15.2. XML Predicates</a></span></dt><dt><span class="sect2"><a href="functions-xml.html#FUNCTIONS-XML-PROCESSING">9.15.3. Processing XML</a></span></dt><dt><span class="sect2"><a href="functions-xml.html#FUNCTIONS-XML-MAPPING">9.15.4. Mapping Tables to XML</a></span></dt></dl></div><a id="id-1.5.8.21.2" class="indexterm"></a><p>
The functions and function-like expressions described in this
section operate on values of type <code class="type">xml</code>. See <a class="xref" href="datatype-xml.html" title="8.13. XML Type">Section 8.13</a> for information about the <code class="type">xml</code>
type. The function-like expressions <code class="function">xmlparse</code>
and <code class="function">xmlserialize</code> for converting to and from
type <code class="type">xml</code> are documented there, not in this section.
</p><p>
Use of most of these functions
requires <span class="productname">PostgreSQL</span> to have been built
with <code class="command">configure --with-libxml</code>.
</p><div class="sect2" id="FUNCTIONS-PRODUCING-XML"><div class="titlepage"><div><div><h3 class="title">9.15.1. Producing XML Content <a href="#FUNCTIONS-PRODUCING-XML" class="id_link">#</a></h3></div></div></div><p>
A set of functions and function-like expressions is available for
producing XML content from SQL data. As such, they are
particularly suitable for formatting query results into XML
documents for processing in client applications.
</p><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLCOMMENT"><div class="titlepage"><div><div><h4 class="title">9.15.1.1. <code class="literal">xmlcomment</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLCOMMENT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.3.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlcomment</code> ( <code class="type">text</code> ) → <code class="returnvalue">xml</code>
</pre><p>
The function <code class="function">xmlcomment</code> creates an XML value
containing an XML comment with the specified text as content.
The text cannot contain <span class="quote">“<span class="quote"><code class="literal">--</code></span>”</span> or end with a
<span class="quote">“<span class="quote"><code class="literal">-</code></span>”</span>, otherwise the resulting construct
would not be a valid XML comment.
If the argument is null, the result is null.
</p><p>
Example:
</p><pre class="screen">
SELECT xmlcomment('hello');
xmlcomment
--------------
<!--hello-->
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLCONCAT"><div class="titlepage"><div><div><h4 class="title">9.15.1.2. <code class="literal">xmlconcat</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLCONCAT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.4.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlconcat</code> ( <code class="type">xml</code> [<span class="optional">, ...</span>] ) → <code class="returnvalue">xml</code>
</pre><p>
The function <code class="function">xmlconcat</code> concatenates a list
of individual XML values to create a single value containing an
XML content fragment. Null values are omitted; the result is
only null if there are no nonnull arguments.
</p><p>
Example:
</p><pre class="screen">
SELECT xmlconcat('<abc/>', '<bar>foo</bar>');
xmlconcat
----------------------
<abc/><bar>foo</bar>
</pre><p>
</p><p>
XML declarations, if present, are combined as follows. If all
argument values have the same XML version declaration, that
version is used in the result, else no version is used. If all
argument values have the standalone declaration value
<span class="quote">“<span class="quote">yes</span>”</span>, then that value is used in the result. If
all argument values have a standalone declaration value and at
least one is <span class="quote">“<span class="quote">no</span>”</span>, then that is used in the result.
Else the result will have no standalone declaration. If the
result is determined to require a standalone declaration but no
version declaration, a version declaration with version 1.0 will
be used because XML requires an XML declaration to contain a
version declaration. Encoding declarations are ignored and
removed in all cases.
</p><p>
Example:
</p><pre class="screen">
SELECT xmlconcat('<?xml version="1.1"?><foo/>', '<?xml version="1.1" standalone="no"?><bar/>');
xmlconcat
-----------------------------------
<?xml version="1.1"?><foo/><bar/>
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLELEMENT"><div class="titlepage"><div><div><h4 class="title">9.15.1.3. <code class="literal">xmlelement</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLELEMENT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.5.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlelement</code> ( <code class="literal">NAME</code> <em class="replaceable"><code>name</code></em> [<span class="optional">, <code class="literal">XMLATTRIBUTES</code> ( <em class="replaceable"><code>attvalue</code></em> [<span class="optional"> <code class="literal">AS</code> <em class="replaceable"><code>attname</code></em> </span>] [<span class="optional">, ...</span>] ) </span>] [<span class="optional">, <em class="replaceable"><code>content</code></em> [<span class="optional">, ...</span>]</span>] ) → <code class="returnvalue">xml</code>
</pre><p>
The <code class="function">xmlelement</code> expression produces an XML
element with the given name, attributes, and content.
The <em class="replaceable"><code>name</code></em>
and <em class="replaceable"><code>attname</code></em> items shown in the syntax are
simple identifiers, not values. The <em class="replaceable"><code>attvalue</code></em>
and <em class="replaceable"><code>content</code></em> items are expressions, which can
yield any <span class="productname">PostgreSQL</span> data type. The
argument(s) within <code class="literal">XMLATTRIBUTES</code> generate attributes
of the XML element; the <em class="replaceable"><code>content</code></em> value(s) are
concatenated to form its content.
</p><p>
Examples:
</p><pre class="screen">
SELECT xmlelement(name foo);
xmlelement
------------
<foo/>
SELECT xmlelement(name foo, xmlattributes('xyz' as bar));
xmlelement
------------------
<foo bar="xyz"/>
SELECT xmlelement(name foo, xmlattributes(current_date as bar), 'cont', 'ent');
xmlelement
-------------------------------------
<foo bar="2007-01-26">content</foo>
</pre><p>
</p><p>
Element and attribute names that are not valid XML names are
escaped by replacing the offending characters by the sequence
<code class="literal">_x<em class="replaceable"><code>HHHH</code></em>_</code>, where
<em class="replaceable"><code>HHHH</code></em> is the character's Unicode
codepoint in hexadecimal notation. For example:
</p><pre class="screen">
SELECT xmlelement(name "foo$bar", xmlattributes('xyz' as "a&b"));
xmlelement
----------------------------------
<foo_x0024_bar a_x0026_b="xyz"/>
</pre><p>
</p><p>
An explicit attribute name need not be specified if the attribute
value is a column reference, in which case the column's name will
be used as the attribute name by default. In other cases, the
attribute must be given an explicit name. So this example is
valid:
</p><pre class="screen">
CREATE TABLE test (a xml, b xml);
SELECT xmlelement(name test, xmlattributes(a, b)) FROM test;
</pre><p>
But these are not:
</p><pre class="screen">
SELECT xmlelement(name test, xmlattributes('constant'), a, b) FROM test;
SELECT xmlelement(name test, xmlattributes(func(a, b))) FROM test;
</pre><p>
</p><p>
Element content, if specified, will be formatted according to
its data type. If the content is itself of type <code class="type">xml</code>,
complex XML documents can be constructed. For example:
</p><pre class="screen">
SELECT xmlelement(name foo, xmlattributes('xyz' as bar),
xmlelement(name abc),
xmlcomment('test'),
xmlelement(name xyz));
xmlelement
----------------------------------------------
<foo bar="xyz"><abc/><!--test--><xyz/></foo>
</pre><p>
Content of other types will be formatted into valid XML character
data. This means in particular that the characters <, >,
and & will be converted to entities. Binary data (data type
<code class="type">bytea</code>) will be represented in base64 or hex
encoding, depending on the setting of the configuration parameter
<a class="xref" href="runtime-config-client.html#GUC-XMLBINARY">xmlbinary</a>. The particular behavior for
individual data types is expected to evolve in order to align the
PostgreSQL mappings with those specified in SQL:2006 and later,
as discussed in <a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-CASTS" title="D.3.1.3. Mappings between SQL and XML Data Types and Values">Section D.3.1.3</a>.
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLFOREST"><div class="titlepage"><div><div><h4 class="title">9.15.1.4. <code class="literal">xmlforest</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLFOREST" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.6.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlforest</code> ( <em class="replaceable"><code>content</code></em> [<span class="optional"> <code class="literal">AS</code> <em class="replaceable"><code>name</code></em> </span>] [<span class="optional">, ...</span>] ) → <code class="returnvalue">xml</code>
</pre><p>
The <code class="function">xmlforest</code> expression produces an XML
forest (sequence) of elements using the given names and content.
As for <code class="function">xmlelement</code>,
each <em class="replaceable"><code>name</code></em> must be a simple identifier, while
the <em class="replaceable"><code>content</code></em> expressions can have any data
type.
</p><p>
Examples:
</p><pre class="screen">
SELECT xmlforest('abc' AS foo, 123 AS bar);
xmlforest
------------------------------
<foo>abc</foo><bar>123</bar>
SELECT xmlforest(table_name, column_name)
FROM information_schema.columns
WHERE table_schema = 'pg_catalog';
xmlforest
-----------------------------------------------------------------------
<table_name>pg_authid</table_name><column_name>rolname</column_name>
<table_name>pg_authid</table_name><column_name>rolsuper</column_name>
...
</pre><p>
As seen in the second example, the element name can be omitted if
the content value is a column reference, in which case the column
name is used by default. Otherwise, a name must be specified.
</p><p>
Element names that are not valid XML names are escaped as shown
for <code class="function">xmlelement</code> above. Similarly, content
data is escaped to make valid XML content, unless it is already
of type <code class="type">xml</code>.
</p><p>
Note that XML forests are not valid XML documents if they consist
of more than one element, so it might be useful to wrap
<code class="function">xmlforest</code> expressions in
<code class="function">xmlelement</code>.
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLPI"><div class="titlepage"><div><div><h4 class="title">9.15.1.5. <code class="literal">xmlpi</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLPI" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.7.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlpi</code> ( <code class="literal">NAME</code> <em class="replaceable"><code>name</code></em> [<span class="optional">, <em class="replaceable"><code>content</code></em> </span>] ) → <code class="returnvalue">xml</code>
</pre><p>
The <code class="function">xmlpi</code> expression creates an XML
processing instruction.
As for <code class="function">xmlelement</code>,
the <em class="replaceable"><code>name</code></em> must be a simple identifier, while
the <em class="replaceable"><code>content</code></em> expression can have any data type.
The <em class="replaceable"><code>content</code></em>, if present, must not contain the
character sequence <code class="literal">?></code>.
</p><p>
Example:
</p><pre class="screen">
SELECT xmlpi(name php, 'echo "hello world";');
xmlpi
-----------------------------
<?php echo "hello world";?>
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-XMLROOT"><div class="titlepage"><div><div><h4 class="title">9.15.1.6. <code class="literal">xmlroot</code> <a href="#FUNCTIONS-PRODUCING-XML-XMLROOT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.8.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlroot</code> ( <code class="type">xml</code>, <code class="literal">VERSION</code> {<code class="type">text</code>|<code class="literal">NO VALUE</code>} [<span class="optional">, <code class="literal">STANDALONE</code> {<code class="literal">YES</code>|<code class="literal">NO</code>|<code class="literal">NO VALUE</code>} </span>] ) → <code class="returnvalue">xml</code>
</pre><p>
The <code class="function">xmlroot</code> expression alters the properties
of the root node of an XML value. If a version is specified,
it replaces the value in the root node's version declaration; if a
standalone setting is specified, it replaces the value in the
root node's standalone declaration.
</p><p>
</p><pre class="screen">
SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'),
version '1.0', standalone yes);
xmlroot
----------------------------------------
<?xml version="1.0" standalone="yes"?>
<content>abc</content>
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-XML-XMLAGG"><div class="titlepage"><div><div><h4 class="title">9.15.1.7. <code class="literal">xmlagg</code> <a href="#FUNCTIONS-XML-XMLAGG" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.5.9.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xmlagg</code> ( <code class="type">xml</code> ) → <code class="returnvalue">xml</code>
</pre><p>
The function <code class="function">xmlagg</code> is, unlike the other
functions described here, an aggregate function. It concatenates the
input values to the aggregate function call,
much like <code class="function">xmlconcat</code> does, except that concatenation
occurs across rows rather than across expressions in a single row.
See <a class="xref" href="functions-aggregate.html" title="9.21. Aggregate Functions">Section 9.21</a> for additional information
about aggregate functions.
</p><p>
Example:
</p><pre class="screen">
CREATE TABLE test (y int, x xml);
INSERT INTO test VALUES (1, '<foo>abc</foo>');
INSERT INTO test VALUES (2, '<bar/>');
SELECT xmlagg(x) FROM test;
xmlagg
----------------------
<foo>abc</foo><bar/>
</pre><p>
</p><p>
To determine the order of the concatenation, an <code class="literal">ORDER BY</code>
clause may be added to the aggregate call as described in
<a class="xref" href="sql-expressions.html#SYNTAX-AGGREGATES" title="4.2.7. Aggregate Expressions">Section 4.2.7</a>. For example:
</p><pre class="screen">
SELECT xmlagg(x ORDER BY y DESC) FROM test;
xmlagg
----------------------
<bar/><foo>abc</foo>
</pre><p>
</p><p>
The following non-standard approach used to be recommended
in previous versions, and may still be useful in specific
cases:
</p><pre class="screen">
SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
xmlagg
----------------------
<bar/><foo>abc</foo>
</pre><p>
</p></div></div><div class="sect2" id="FUNCTIONS-XML-PREDICATES"><div class="titlepage"><div><div><h3 class="title">9.15.2. XML Predicates <a href="#FUNCTIONS-XML-PREDICATES" class="id_link">#</a></h3></div></div></div><p>
The expressions described in this section check properties
of <code class="type">xml</code> values.
</p><div class="sect3" id="FUNCTIONS-PRODUCING-XML-IS-DOCUMENT"><div class="titlepage"><div><div><h4 class="title">9.15.2.1. <code class="literal">IS DOCUMENT</code> <a href="#FUNCTIONS-PRODUCING-XML-IS-DOCUMENT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.6.3.2" class="indexterm"></a><pre class="synopsis">
<code class="type">xml</code> <code class="literal">IS DOCUMENT</code> → <code class="returnvalue">boolean</code>
</pre><p>
The expression <code class="literal">IS DOCUMENT</code> returns true if the
argument XML value is a proper XML document, false if it is not
(that is, it is a content fragment), or null if the argument is
null. See <a class="xref" href="datatype-xml.html" title="8.13. XML Type">Section 8.13</a> about the difference
between documents and content fragments.
</p></div><div class="sect3" id="FUNCTIONS-PRODUCING-XML-IS-NOT-DOCUMENT"><div class="titlepage"><div><div><h4 class="title">9.15.2.2. <code class="literal">IS NOT DOCUMENT</code> <a href="#FUNCTIONS-PRODUCING-XML-IS-NOT-DOCUMENT" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.6.4.2" class="indexterm"></a><pre class="synopsis">
<code class="type">xml</code> <code class="literal">IS NOT DOCUMENT</code> → <code class="returnvalue">boolean</code>
</pre><p>
The expression <code class="literal">IS NOT DOCUMENT</code> returns false if the
argument XML value is a proper XML document, true if it is not (that is,
it is a content fragment), or null if the argument is null.
</p></div><div class="sect3" id="XML-EXISTS"><div class="titlepage"><div><div><h4 class="title">9.15.2.3. <code class="literal">XMLEXISTS</code> <a href="#XML-EXISTS" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.6.5.2" class="indexterm"></a><pre class="synopsis">
<code class="function">XMLEXISTS</code> ( <code class="type">text</code> <code class="literal">PASSING</code> [<span class="optional"><code class="literal">BY</code> {<code class="literal">REF</code>|<code class="literal">VALUE</code>}</span>] <code class="type">xml</code> [<span class="optional"><code class="literal">BY</code> {<code class="literal">REF</code>|<code class="literal">VALUE</code>}</span>] ) → <code class="returnvalue">boolean</code>
</pre><p>
The function <code class="function">xmlexists</code> evaluates an XPath 1.0
expression (the first argument), with the passed XML value as its context
item. The function returns false if the result of that evaluation
yields an empty node-set, true if it yields any other value. The
function returns null if any argument is null. A nonnull value
passed as the context item must be an XML document, not a content
fragment or any non-XML value.
</p><p>
Example:
</p><pre class="screen">
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY VALUE '<towns><town>Toronto</town><town>Ottawa</town></towns>');
xmlexists
------------
t
(1 row)
</pre><p>
</p><p>
The <code class="literal">BY REF</code> and <code class="literal">BY VALUE</code> clauses
are accepted in <span class="productname">PostgreSQL</span>, but are ignored,
as discussed in <a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-POSTGRESQL" title="D.3.2. Incidental Limits of the Implementation">Section D.3.2</a>.
</p><p>
In the SQL standard, the <code class="function">xmlexists</code> function
evaluates an expression in the XML Query language,
but <span class="productname">PostgreSQL</span> allows only an XPath 1.0
expression, as discussed in
<a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-XPATH1" title="D.3.1. Queries Are Restricted to XPath 1.0">Section D.3.1</a>.
</p></div><div class="sect3" id="XML-IS-WELL-FORMED"><div class="titlepage"><div><div><h4 class="title">9.15.2.4. <code class="literal">xml_is_well_formed</code> <a href="#XML-IS-WELL-FORMED" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.6.6.2" class="indexterm"></a><a id="id-1.5.8.21.6.6.3" class="indexterm"></a><a id="id-1.5.8.21.6.6.4" class="indexterm"></a><pre class="synopsis">
<code class="function">xml_is_well_formed</code> ( <code class="type">text</code> ) → <code class="returnvalue">boolean</code>
<code class="function">xml_is_well_formed_document</code> ( <code class="type">text</code> ) → <code class="returnvalue">boolean</code>
<code class="function">xml_is_well_formed_content</code> ( <code class="type">text</code> ) → <code class="returnvalue">boolean</code>
</pre><p>
These functions check whether a <code class="type">text</code> string represents
well-formed XML, returning a Boolean result.
<code class="function">xml_is_well_formed_document</code> checks for a well-formed
document, while <code class="function">xml_is_well_formed_content</code> checks
for well-formed content. <code class="function">xml_is_well_formed</code> does
the former if the <a class="xref" href="runtime-config-client.html#GUC-XMLOPTION">xmloption</a> configuration
parameter is set to <code class="literal">DOCUMENT</code>, or the latter if it is set to
<code class="literal">CONTENT</code>. This means that
<code class="function">xml_is_well_formed</code> is useful for seeing whether
a simple cast to type <code class="type">xml</code> will succeed, whereas the other two
functions are useful for seeing whether the corresponding variants of
<code class="function">XMLPARSE</code> will succeed.
</p><p>
Examples:
</p><pre class="screen">
SET xmloption TO DOCUMENT;
SELECT xml_is_well_formed('<>');
xml_is_well_formed
--------------------
f
(1 row)
SELECT xml_is_well_formed('<abc/>');
xml_is_well_formed
--------------------
t
(1 row)
SET xmloption TO CONTENT;
SELECT xml_is_well_formed('abc');
xml_is_well_formed
--------------------
t
(1 row)
SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuff">bar</pg:foo>');
xml_is_well_formed_document
-----------------------------
t
(1 row)
SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuff">bar</my:foo>');
xml_is_well_formed_document
-----------------------------
f
(1 row)
</pre><p>
The last example shows that the checks include whether
namespaces are correctly matched.
</p></div></div><div class="sect2" id="FUNCTIONS-XML-PROCESSING"><div class="titlepage"><div><div><h3 class="title">9.15.3. Processing XML <a href="#FUNCTIONS-XML-PROCESSING" class="id_link">#</a></h3></div></div></div><p>
To process values of data type <code class="type">xml</code>, PostgreSQL offers
the functions <code class="function">xpath</code> and
<code class="function">xpath_exists</code>, which evaluate XPath 1.0
expressions, and the <code class="function">XMLTABLE</code>
table function.
</p><div class="sect3" id="FUNCTIONS-XML-PROCESSING-XPATH"><div class="titlepage"><div><div><h4 class="title">9.15.3.1. <code class="literal">xpath</code> <a href="#FUNCTIONS-XML-PROCESSING-XPATH" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.7.3.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xpath</code> ( <em class="parameter"><code>xpath</code></em> <code class="type">text</code>, <em class="parameter"><code>xml</code></em> <code class="type">xml</code> [<span class="optional">, <em class="parameter"><code>nsarray</code></em> <code class="type">text[]</code> </span>] ) → <code class="returnvalue">xml[]</code>
</pre><p>
The function <code class="function">xpath</code> evaluates the XPath 1.0
expression <em class="parameter"><code>xpath</code></em> (given as text)
against the XML value
<em class="parameter"><code>xml</code></em>. It returns an array of XML values
corresponding to the node-set produced by the XPath expression.
If the XPath expression returns a scalar value rather than a node-set,
a single-element array is returned.
</p><p>
The second argument must be a well formed XML document. In particular,
it must have a single root node element.
</p><p>
The optional third argument of the function is an array of namespace
mappings. This array should be a two-dimensional <code class="type">text</code> array with
the length of the second axis being equal to 2 (i.e., it should be an
array of arrays, each of which consists of exactly 2 elements).
The first element of each array entry is the namespace name (alias), the
second the namespace URI. It is not required that aliases provided in
this array be the same as those being used in the XML document itself (in
other words, both in the XML document and in the <code class="function">xpath</code>
function context, aliases are <span class="emphasis"><em>local</em></span>).
</p><p>
Example:
</p><pre class="screen">
SELECT xpath('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
ARRAY[ARRAY['my', 'http://example.com']]);
xpath
--------
{test}
(1 row)
</pre><p>
</p><p>
To deal with default (anonymous) namespaces, do something like this:
</p><pre class="screen">
SELECT xpath('//mydefns:b/text()', '<a xmlns="http://example.com"><b>test</b></a>',
ARRAY[ARRAY['mydefns', 'http://example.com']]);
xpath
--------
{test}
(1 row)
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-XML-PROCESSING-XPATH-EXISTS"><div class="titlepage"><div><div><h4 class="title">9.15.3.2. <code class="literal">xpath_exists</code> <a href="#FUNCTIONS-XML-PROCESSING-XPATH-EXISTS" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.7.4.2" class="indexterm"></a><pre class="synopsis">
<code class="function">xpath_exists</code> ( <em class="parameter"><code>xpath</code></em> <code class="type">text</code>, <em class="parameter"><code>xml</code></em> <code class="type">xml</code> [<span class="optional">, <em class="parameter"><code>nsarray</code></em> <code class="type">text[]</code> </span>] ) → <code class="returnvalue">boolean</code>
</pre><p>
The function <code class="function">xpath_exists</code> is a specialized form
of the <code class="function">xpath</code> function. Instead of returning the
individual XML values that satisfy the XPath 1.0 expression, this function
returns a Boolean indicating whether the query was satisfied or not
(specifically, whether it produced any value other than an empty node-set).
This function is equivalent to the <code class="literal">XMLEXISTS</code> predicate,
except that it also offers support for a namespace mapping argument.
</p><p>
Example:
</p><pre class="screen">
SELECT xpath_exists('/my:a/text()', '<my:a xmlns:my="http://example.com">test</my:a>',
ARRAY[ARRAY['my', 'http://example.com']]);
xpath_exists
--------------
t
(1 row)
</pre><p>
</p></div><div class="sect3" id="FUNCTIONS-XML-PROCESSING-XMLTABLE"><div class="titlepage"><div><div><h4 class="title">9.15.3.3. <code class="literal">xmltable</code> <a href="#FUNCTIONS-XML-PROCESSING-XMLTABLE" class="id_link">#</a></h4></div></div></div><a id="id-1.5.8.21.7.5.2" class="indexterm"></a><a id="id-1.5.8.21.7.5.3" class="indexterm"></a><pre class="synopsis">
<code class="function">XMLTABLE</code> (
[<span class="optional"> <code class="literal">XMLNAMESPACES</code> ( <em class="replaceable"><code>namespace_uri</code></em> <code class="literal">AS</code> <em class="replaceable"><code>namespace_name</code></em> [<span class="optional">, ...</span>] ), </span>]
<em class="replaceable"><code>row_expression</code></em> <code class="literal">PASSING</code> [<span class="optional"><code class="literal">BY</code> {<code class="literal">REF</code>|<code class="literal">VALUE</code>}</span>] <em class="replaceable"><code>document_expression</code></em> [<span class="optional"><code class="literal">BY</code> {<code class="literal">REF</code>|<code class="literal">VALUE</code>}</span>]
<code class="literal">COLUMNS</code> <em class="replaceable"><code>name</code></em> { <em class="replaceable"><code>type</code></em> [<span class="optional"><code class="literal">PATH</code> <em class="replaceable"><code>column_expression</code></em></span>] [<span class="optional"><code class="literal">DEFAULT</code> <em class="replaceable"><code>default_expression</code></em></span>] [<span class="optional"><code class="literal">NOT NULL</code> | <code class="literal">NULL</code></span>]
| <code class="literal">FOR ORDINALITY</code> }
[<span class="optional">, ...</span>]
) → <code class="returnvalue">setof record</code>
</pre><p>
The <code class="function">xmltable</code> expression produces a table based
on an XML value, an XPath filter to extract rows, and a
set of column definitions.
Although it syntactically resembles a function, it can only appear
as a table in a query's <code class="literal">FROM</code> clause.
</p><p>
The optional <code class="literal">XMLNAMESPACES</code> clause gives a
comma-separated list of namespace definitions, where
each <em class="replaceable"><code>namespace_uri</code></em> is a <code class="type">text</code>
expression and each <em class="replaceable"><code>namespace_name</code></em> is a simple
identifier. It specifies the XML namespaces used in the document and
their aliases. A default namespace specification is not currently
supported.
</p><p>
The required <em class="replaceable"><code>row_expression</code></em> argument is an
XPath 1.0 expression (given as <code class="type">text</code>) that is evaluated,
passing the XML value <em class="replaceable"><code>document_expression</code></em> as
its context item, to obtain a set of XML nodes. These nodes are what
<code class="function">xmltable</code> transforms into output rows. No rows
will be produced if the <em class="replaceable"><code>document_expression</code></em>
is null, nor if the <em class="replaceable"><code>row_expression</code></em> produces
an empty node-set or any value other than a node-set.
</p><p>
<em class="replaceable"><code>document_expression</code></em> provides the context
item for the <em class="replaceable"><code>row_expression</code></em>. It must be a
well-formed XML document; fragments/forests are not accepted.
The <code class="literal">BY REF</code> and <code class="literal">BY VALUE</code> clauses
are accepted but ignored, as discussed in
<a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-POSTGRESQL" title="D.3.2. Incidental Limits of the Implementation">Section D.3.2</a>.
</p><p>
In the SQL standard, the <code class="function">xmltable</code> function
evaluates expressions in the XML Query language,
but <span class="productname">PostgreSQL</span> allows only XPath 1.0
expressions, as discussed in
<a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-XPATH1" title="D.3.1. Queries Are Restricted to XPath 1.0">Section D.3.1</a>.
</p><p>
The required <code class="literal">COLUMNS</code> clause specifies the
column(s) that will be produced in the output table.
See the syntax summary above for the format.
A name is required for each column, as is a data type
(unless <code class="literal">FOR ORDINALITY</code> is specified, in which case
type <code class="type">integer</code> is implicit). The path, default and
nullability clauses are optional.
</p><p>
A column marked <code class="literal">FOR ORDINALITY</code> will be populated
with row numbers, starting with 1, in the order of nodes retrieved from
the <em class="replaceable"><code>row_expression</code></em>'s result node-set.
At most one column may be marked <code class="literal">FOR ORDINALITY</code>.
</p><div class="note"><h3 class="title">Note</h3><p>
XPath 1.0 does not specify an order for nodes in a node-set, so code
that relies on a particular order of the results will be
implementation-dependent. Details can be found in
<a class="xref" href="xml-limits-conformance.html#XML-XPATH-1-SPECIFICS" title="D.3.1.2. Restriction of XPath to 1.0">Section D.3.1.2</a>.
</p></div><p>
The <em class="replaceable"><code>column_expression</code></em> for a column is an
XPath 1.0 expression that is evaluated for each row, with the current
node from the <em class="replaceable"><code>row_expression</code></em> result as its
context item, to find the value of the column. If
no <em class="replaceable"><code>column_expression</code></em> is given, then the
column name is used as an implicit path.
</p><p>
If a column's XPath expression returns a non-XML value (which is limited
to string, boolean, or double in XPath 1.0) and the column has a
PostgreSQL type other than <code class="type">xml</code>, the column will be set
as if by assigning the value's string representation to the PostgreSQL
type. (If the value is a boolean, its string representation is taken
to be <code class="literal">1</code> or <code class="literal">0</code> if the output
column's type category is numeric, otherwise <code class="literal">true</code> or
<code class="literal">false</code>.)
</p><p>
If a column's XPath expression returns a non-empty set of XML nodes
and the column's PostgreSQL type is <code class="type">xml</code>, the column will
be assigned the expression result exactly, if it is of document or
content form.
<a href="#ftn.id-1.5.8.21.7.5.15.2" class="footnote"><sup class="footnote" id="id-1.5.8.21.7.5.15.2">[8]</sup></a>
</p><p>
A non-XML result assigned to an <code class="type">xml</code> output column produces
content, a single text node with the string value of the result.
An XML result assigned to a column of any other type may not have more than
one node, or an error is raised. If there is exactly one node, the column
will be set as if by assigning the node's string
value (as defined for the XPath 1.0 <code class="function">string</code> function)
to the PostgreSQL type.
</p><p>
The string value of an XML element is the concatenation, in document order,
of all text nodes contained in that element and its descendants. The string
value of an element with no descendant text nodes is an
empty string (not <code class="literal">NULL</code>).
Any <code class="literal">xsi:nil</code> attributes are ignored.
Note that the whitespace-only <code class="literal">text()</code> node between two non-text
elements is preserved, and that leading whitespace on a <code class="literal">text()</code>
node is not flattened.
The XPath 1.0 <code class="function">string</code> function may be consulted for the
rules defining the string value of other XML node types and non-XML values.
</p><p>
The conversion rules presented here are not exactly those of the SQL
standard, as discussed in <a class="xref" href="xml-limits-conformance.html#FUNCTIONS-XML-LIMITS-CASTS" title="D.3.1.3. Mappings between SQL and XML Data Types and Values">Section D.3.1.3</a>.
</p><p>
If the path expression returns an empty node-set
(typically, when it does not match)
for a given row, the column will be set to <code class="literal">NULL</code>, unless
a <em class="replaceable"><code>default_expression</code></em> is specified; then the
value resulting from evaluating that expression is used.
</p><p>
A <em class="replaceable"><code>default_expression</code></em>, rather than being
evaluated immediately when <code class="function">xmltable</code> is called,
is evaluated each time a default is needed for the column.
If the expression qualifies as stable or immutable, the repeat
evaluation may be skipped.
This means that you can usefully use volatile functions like
<code class="function">nextval</code> in
<em class="replaceable"><code>default_expression</code></em>.
</p><p>
Columns may be marked <code class="literal">NOT NULL</code>. If the
<em class="replaceable"><code>column_expression</code></em> for a <code class="literal">NOT
NULL</code> column does not match anything and there is
no <code class="literal">DEFAULT</code> or
the <em class="replaceable"><code>default_expression</code></em> also evaluates to null,
an error is reported.
</p><p>
Examples:
</p><pre class="screen">
CREATE TABLE xmldata AS SELECT
xml $$
<ROWS>
<ROW id="1">
<COUNTRY_ID>AU</COUNTRY_ID>
<COUNTRY_NAME>Australia</COUNTRY_NAME>
</ROW>
<ROW id="5">
<COUNTRY_ID>JP</COUNTRY_ID>
<COUNTRY_NAME>Japan</COUNTRY_NAME>
<PREMIER_NAME>Shinzo Abe</PREMIER_NAME>
<SIZE unit="sq_mi">145935</SIZE>
</ROW>
<ROW id="6">
<COUNTRY_ID>SG</COUNTRY_ID>
<COUNTRY_NAME>Singapore</COUNTRY_NAME>
<SIZE unit="sq_km">697</SIZE>
</ROW>
</ROWS>
$$ AS data;
SELECT xmltable.*
FROM xmldata,
XMLTABLE('//ROWS/ROW'
PASSING data
COLUMNS id int PATH '@id',
ordinality FOR ORDINALITY,
"COUNTRY_NAME" text,
country_id text PATH 'COUNTRY_ID',
size_sq_km float PATH 'SIZE[@unit = "sq_km"]',
size_other text PATH
'concat(SIZE[@unit!="sq_km"], " ", SIZE[@unit!="sq_km"]/@unit)',
premier_name text PATH 'PREMIER_NAME' DEFAULT 'not specified');
id | ordinality | COUNTRY_NAME | country_id | size_sq_km | size_other | premier_name
----+------------+--------------+------------+------------+--------------+---------------
1 | 1 | Australia | AU | | | not specified
5 | 2 | Japan | JP | | 145935 sq_mi | Shinzo Abe
6 | 3 | Singapore | SG | 697 | | not specified
</pre><p>
The following example shows concatenation of multiple text() nodes,
usage of the column name as XPath filter, and the treatment of whitespace,
XML comments and processing instructions:
</p><pre class="screen">
CREATE TABLE xmlelements AS SELECT
xml $$
<root>
<element> Hello<!-- xyxxz -->2a2<?aaaaa?> <!--x--> bbb<x>xxx</x>CC </element>
</root>
$$ AS data;
SELECT xmltable.*
FROM xmlelements, XMLTABLE('/root' PASSING data COLUMNS element text);
element
-------------------------
Hello2a2 bbbxxxCC
</pre><p>
</p><p>
The following example illustrates how
the <code class="literal">XMLNAMESPACES</code> clause can be used to specify
a list of namespaces
used in the XML document as well as in the XPath expressions:
</p><pre class="screen">
WITH xmldata(data) AS (VALUES ('
<example xmlns="http://example.com/myns" xmlns:B="http://example.com/b">
<item foo="1" B:bar="2"/>
<item foo="3" B:bar="4"/>
<item foo="4" B:bar="5"/>
</example>'::xml)
)
SELECT xmltable.*
FROM XMLTABLE(XMLNAMESPACES('http://example.com/myns' AS x,
'http://example.com/b' AS "B"),
'/x:example/x:item'
PASSING (SELECT data FROM xmldata)
COLUMNS foo int PATH '@foo',
bar int PATH '@B:bar');
foo | bar
-----+-----
1 | 2
3 | 4
4 | 5
(3 rows)
</pre><p>
</p></div></div><div class="sect2" id="FUNCTIONS-XML-MAPPING"><div class="titlepage"><div><div><h3 class="title">9.15.4. Mapping Tables to XML <a href="#FUNCTIONS-XML-MAPPING" class="id_link">#</a></h3></div></div></div><a id="id-1.5.8.21.8.2" class="indexterm"></a><p>
The following functions map the contents of relational tables to
XML values. They can be thought of as XML export functionality:
</p><pre class="synopsis">
<code class="function">table_to_xml</code> ( <em class="parameter"><code>table</code></em> <code class="type">regclass</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">query_to_xml</code> ( <em class="parameter"><code>query</code></em> <code class="type">text</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">cursor_to_xml</code> ( <em class="parameter"><code>cursor</code></em> <code class="type">refcursor</code>, <em class="parameter"><code>count</code></em> <code class="type">integer</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
</pre><p>
</p><p>
<code class="function">table_to_xml</code> maps the content of the named
table, passed as parameter <em class="parameter"><code>table</code></em>. The
<code class="type">regclass</code> type accepts strings identifying tables using the
usual notation, including optional schema qualification and
double quotes (see <a class="xref" href="datatype-oid.html" title="8.19. Object Identifier Types">Section 8.19</a> for details).
<code class="function">query_to_xml</code> executes the
query whose text is passed as parameter
<em class="parameter"><code>query</code></em> and maps the result set.
<code class="function">cursor_to_xml</code> fetches the indicated number of
rows from the cursor specified by the parameter
<em class="parameter"><code>cursor</code></em>. This variant is recommended if
large tables have to be mapped, because the result value is built
up in memory by each function.
</p><p>
If <em class="parameter"><code>tableforest</code></em> is false, then the resulting
XML document looks like this:
</p><pre class="screen">
<tablename>
<row>
<columnname1>data</columnname1>
<columnname2>data</columnname2>
</row>
<row>
...
</row>
...
</tablename>
</pre><p>
If <em class="parameter"><code>tableforest</code></em> is true, the result is an
XML content fragment that looks like this:
</p><pre class="screen">
<tablename>
<columnname1>data</columnname1>
<columnname2>data</columnname2>
</tablename>
<tablename>
...
</tablename>
...
</pre><p>
If no table name is available, that is, when mapping a query or a
cursor, the string <code class="literal">table</code> is used in the first
format, <code class="literal">row</code> in the second format.
</p><p>
The choice between these formats is up to the user. The first
format is a proper XML document, which will be important in many
applications. The second format tends to be more useful in the
<code class="function">cursor_to_xml</code> function if the result values are to be
reassembled into one document later on. The functions for
producing XML content discussed above, in particular
<code class="function">xmlelement</code>, can be used to alter the results
to taste.
</p><p>
The data values are mapped in the same way as described for the
function <code class="function">xmlelement</code> above.
</p><p>
The parameter <em class="parameter"><code>nulls</code></em> determines whether null
values should be included in the output. If true, null values in
columns are represented as:
</p><pre class="screen">
<columnname xsi:nil="true"/>
</pre><p>
where <code class="literal">xsi</code> is the XML namespace prefix for XML
Schema Instance. An appropriate namespace declaration will be
added to the result value. If false, columns containing null
values are simply omitted from the output.
</p><p>
The parameter <em class="parameter"><code>targetns</code></em> specifies the
desired XML namespace of the result. If no particular namespace
is wanted, an empty string should be passed.
</p><p>
The following functions return XML Schema documents describing the
mappings performed by the corresponding functions above:
</p><pre class="synopsis">
<code class="function">table_to_xmlschema</code> ( <em class="parameter"><code>table</code></em> <code class="type">regclass</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">query_to_xmlschema</code> ( <em class="parameter"><code>query</code></em> <code class="type">text</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">cursor_to_xmlschema</code> ( <em class="parameter"><code>cursor</code></em> <code class="type">refcursor</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
</pre><p>
It is essential that the same parameters are passed in order to
obtain matching XML data mappings and XML Schema documents.
</p><p>
The following functions produce XML data mappings and the
corresponding XML Schema in one document (or forest), linked
together. They can be useful where self-contained and
self-describing results are wanted:
</p><pre class="synopsis">
<code class="function">table_to_xml_and_xmlschema</code> ( <em class="parameter"><code>table</code></em> <code class="type">regclass</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">query_to_xml_and_xmlschema</code> ( <em class="parameter"><code>query</code></em> <code class="type">text</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
</pre><p>
</p><p>
In addition, the following functions are available to produce
analogous mappings of entire schemas or the entire current
database:
</p><pre class="synopsis">
<code class="function">schema_to_xml</code> ( <em class="parameter"><code>schema</code></em> <code class="type">name</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">schema_to_xmlschema</code> ( <em class="parameter"><code>schema</code></em> <code class="type">name</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">schema_to_xml_and_xmlschema</code> ( <em class="parameter"><code>schema</code></em> <code class="type">name</code>, <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">database_to_xml</code> ( <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">database_to_xmlschema</code> ( <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
<code class="function">database_to_xml_and_xmlschema</code> ( <em class="parameter"><code>nulls</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>tableforest</code></em> <code class="type">boolean</code>, <em class="parameter"><code>targetns</code></em> <code class="type">text</code> ) → <code class="returnvalue">xml</code>
</pre><p>
These functions ignore tables that are not readable by the current user.
The database-wide functions additionally ignore schemas that the current
user does not have <code class="literal">USAGE</code> (lookup) privilege for.
</p><p>
Note that these potentially produce a lot of data, which needs to
be built up in memory. When requesting content mappings of large
schemas or databases, it might be worthwhile to consider mapping the
tables separately instead, possibly even through a cursor.
</p><p>
The result of a schema content mapping looks like this:
</p><pre class="screen">
<schemaname>
table1-mapping
table2-mapping
...
</schemaname></pre><p>
where the format of a table mapping depends on the
<em class="parameter"><code>tableforest</code></em> parameter as explained above.
</p><p>
The result of a database content mapping looks like this:
</p><pre class="screen">
<dbname>
<schema1name>
...
</schema1name>
<schema2name>
...
</schema2name>
...
</dbname></pre><p>
where the schema mapping is as above.
</p><p>
As an example of using the output produced by these functions,
<a class="xref" href="functions-xml.html#XSLT-XML-HTML" title="Example 9.1. XSLT Stylesheet for Converting SQL/XML Output to HTML">Example 9.1</a> shows an XSLT stylesheet that
converts the output of
<code class="function">table_to_xml_and_xmlschema</code> to an HTML
document containing a tabular rendition of the table data. In a
similar manner, the results from these functions can be
converted into other XML-based formats.
</p><div class="example" id="XSLT-XML-HTML"><p class="title"><strong>Example 9.1. XSLT Stylesheet for Converting SQL/XML Output to HTML</strong></p><div class="example-contents"><pre class="programlisting">
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://www.w3.org/1999/xhtml"
>
<xsl:output method="xml"
doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"
doctype-public="-//W3C/DTD XHTML 1.0 Strict//EN"
indent="yes"/>
<xsl:template match="/*">
<xsl:variable name="schema" select="//xsd:schema"/>
<xsl:variable name="tabletypename"
select="$schema/xsd:element[@name=name(current())]/@type"/>
<xsl:variable name="rowtypename"
select="$schema/xsd:complexType[@name=$tabletypename]/xsd:sequence/xsd:element[@name='row']/@type"/>
<html>
<head>
<title><xsl:value-of select="name(current())"/></title>
</head>
<body>
<table>
<tr>
<xsl:for-each select="$schema/xsd:complexType[@name=$rowtypename]/xsd:sequence/xsd:element/@name">
<th><xsl:value-of select="."/></th>
</xsl:for-each>
</tr>
<xsl:for-each select="row">
<tr>
<xsl:for-each select="*">
<td><xsl:value-of select="."/></td>
</xsl:for-each>
</tr>
</xsl:for-each>
</table>
</body>
</html>
</xsl:template>
</xsl:stylesheet>
</pre></div></div><br class="example-break" /></div><div class="footnotes"><br /><hr style="width:100; text-align:left;margin-left: 0" /><div id="ftn.id-1.5.8.21.7.5.15.2" class="footnote"><p><a href="#id-1.5.8.21.7.5.15.2" class="para"><sup class="para">[8] </sup></a>
A result containing more than one element node at the top level, or
non-whitespace text outside of an element, is an example of content form.
An XPath result can be of neither form, for example if it returns an
attribute node selected from the element that contains it. Such a result
will be put into content form with each such disallowed node replaced by
its string value, as defined for the XPath 1.0
<code class="function">string</code> function.
</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-uuid.html" title="9.14. UUID Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-json.html" title="9.16. JSON Functions and Operators">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.14. UUID Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.16. JSON Functions and Operators</td></tr></table></div></body></html>