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Update documentation on XML functions
This commit is contained in:
Peter Eisentraut
parent
b39e91501c
commit
48ba3f5711
@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.186 2007/01/25 11:53:50 petere Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.187 2007/01/29 13:24:30 petere Exp $ -->
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<chapter id="datatype">
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<title id="datatype-title">Data Types</title>
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@ -3538,86 +3538,6 @@ SET xmloption TO { DOCUMENT | CONTENT };
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processed in UTF-8, computations will be most efficient if the
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server encoding is also UTF-8.
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</para>
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<para>
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<acronym>XML</> (Extensible Markup Language) support is not
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just the existance of an <type>xml</type> data type, but a
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variety of features supported by a database system. These
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capabilities include import/export, indexing, searching,
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transforming, and <acronym>XML</> to <acronym>SQL</> mapping.
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<productname>PostgreSQL</> supports some but not all of these
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<acronym>XML</> capabilities. For an overview of <acronym>XML</>
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use in databases, see <ulink
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url="http://www.rpbourret.com/xml/XMLAndDatabases.htm"></>.
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</para>
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<variablelist>
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<varlistentry>
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<term>Import/Export</term>
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<listitem>
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<para>
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There is no facility for mapping <acronym>XML</> to relational
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tables. An external tool must be used for this. One simple way to
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export <acronym>XML</> is to use <application>psql</> in
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<acronym>HTML</> mode (<literal>\pset format html</>), and convert
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the <acronym>XHTML</> output to XML using an external tool.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Indexing</term>
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<listitem>
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<para>
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<filename>/contrib/xml2</> functions can be used in expression
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indexes to index specific <acronym>XML</> fields. To index the
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full contents of <acronym>XML</> documents, the full-text indexing
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tool <filename>/contrib/tsearch2</> can be used. Of course,
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Tsearch2 indexes have no <acronym>XML</> awareness so additional
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<filename>/contrib/xml2</> checks should be added to queries.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Searching</term>
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<listitem>
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<para>
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XPath searches are implemented using <filename>/contrib/xml2</>.
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It processes <acronym>XML</> text documents and returns results
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based on the requested query.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Transforming</term>
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<listitem>
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<para>
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<filename>/contrib/xml2</> supports <acronym>XSLT</> (Extensible
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Stylesheet Language Transformation).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>XML to SQL Mapping</term>
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<listitem>
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<para>
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This involves converting <acronym>XML</> data to and from
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relational structures. <productname>PostgreSQL</> has no internal
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support for such mapping, and relies on external tools to do such
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conversions.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect1>
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</chapter>
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.352 2007/01/20 21:59:34 neilc Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.353 2007/01/29 13:24:30 petere Exp $ -->
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<chapter id="functions">
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<title>Functions and Operators</title>
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@ -10752,65 +10752,215 @@ SELECT (pg_stat_file('filename')).modification;
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</sect1>
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<sect1 id="functions-xml">
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<title>XML Functions</title>
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<sect1 id="functions-xml">
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<title>XML Functions</title>
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<para>
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The functions and function-like expressions described in this
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section operate on values of type <type>xml</type>. Check <xref
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linkend="datatype-xml"> for information about the <type>xml</type>
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type. The function-like expressions <function>xmlparse</function>
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and <function>xmlserialize</function> for converting to and from
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type <type>xml</type> are not repeated here.
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</para>
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<sect2>
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<title>Producing XML Content</title>
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<para>
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The functions and function-like expressions described in this
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section operate on values of type <type>xml</type>.
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A set of functions and function-like expressions are available for
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producing XML content from SQL data. As such, they are
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particularly suitable for formatting query results into XML
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documents for processing in client applications.
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</para>
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<sect2>
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<sect3>
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<title><literal>xmlcomment</literal></title>
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<indexterm>
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<primary>xmlcomment</primary>
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</indexterm>
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<synopsis>
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<function>xmlcomment</function>(<replaceable>text</replaceable>)
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</synopsis>
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<indexterm>
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<primary>xmlcomment</primary>
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</indexterm>
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<synopsis>
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<function>xmlcomment</function>(<replaceable>text</replaceable>)
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</synopsis>
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<para>
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Creates an XML comment.
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The function <function>xmlcomment</function> creates an XML value
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containing an XML comment with the specified text as content.
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The text may not contain <literal>--</literal> or end with a
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<literal>-</literal> so that the resulting construct is a valid
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XML comment. If the argument is null, the result is null.
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</para>
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</sect2>
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<sect2>
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<para>
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Example:
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<screen><![CDATA[
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SELECT xmlcomment('hello');
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xmlcomment
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--------------
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<!--hello-->
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]]></screen>
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</para>
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</sect3>
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<sect3>
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<title><literal>xmlconcat</literal></title>
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<indexterm>
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<primary>xmlconcat</primary>
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</indexterm>
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<indexterm>
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<primary>xmlconcat</primary>
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</indexterm>
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<synopsis>
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<function>xmlconcat</function>(<replaceable>xml</replaceable><optional>, xml, ...</optional>)
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<function>xmlconcat</function>(<replaceable>xml</replaceable><optional>, ...</optional>)
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</synopsis>
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<para>
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Combines a list of individual XML values to create a
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single value containing an XML forest.
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The function <function>xmlconcat</function> concatenates a list
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of individual XML values to create a single value containing an
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XML content fragment. Null values are omitted; the result is
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only null if there are no nonnull arguments.
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</para>
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</sect2>
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<para>
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Example:
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<screen><![CDATA[
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SELECT xmlconcat('<abc/>', '<bar>foo</bar>');
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xmlconcat
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----------------------
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<abc/><bar>foo</bar>
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]]></screen>
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</para>
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<para>
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XML declarations, if present are combined as follows. If all
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argument values have the same XML version declaration, that
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version is used in the result, else no version is used. If all
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argument values have the standalone declaration value
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<quote>yes</quote>, then that value is used in the result. If
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all argument values have a standalone declaration value and at
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least one is <quote>no</quote>, then that is used in the result.
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Else the result will have no standalone declaration. If the
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result is determined to require a standalone declaration but no
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version declaration, a version declaration with version 1.0 will
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be used because XML requires an XML declaration to contain a
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version declaration. Encoding declarations are ignored and
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removed in all cases.
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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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SELECT xmlconcat('<?xml version="1.1"?><foo/>', '<?xml version="1.1" standalone="no"?><bar/>');
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xmlconcat
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-----------------------------------
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<?xml version="1.1"?><foo/><bar/>
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]]></screen>
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</para>
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</sect3>
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<sect2>
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<sect3>
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<title><literal>xmlelement</literal></title>
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<indexterm>
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<primary>xmlelement</primary>
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</indexterm>
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<synopsis>
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<function>xmlelement</function>(name <replaceable>name</replaceable><optional>, xmlattribytes(<replaceable>value</replaceable> <optional>AS <replaceable>label</replaceable></optional><optional>, ... </optional>)</optional>
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<optional><replaceable>, content, ...</replaceable></optional>)
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<synopsis>
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<function>xmlelement</function>(name <replaceable>name</replaceable> <optional>, xmlattributes(<replaceable>value</replaceable> <optional>AS <replaceable>attname</replaceable></optional> <optional>, ... </optional>)</optional> <optional><replaceable>, content, ...</replaceable></optional>)
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</synopsis>
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<para>
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Creates an XML element, allowing the name to be specified.
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The <function>xmlelement</function> expression produces an XML
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element with the given name, attributes, and content.
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</para>
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</sect2>
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<para>
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Examples:
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<screen><![CDATA[
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SELECT xmlelement(name foo);
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xmlelement
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------------
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<foo/>
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SELECT xmlelement(name foo, xmlattributes('xyz' as bar));
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xmlelement
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------------------
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<foo bar="xyz"/>
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SELECT xmlelement(name foo, xmlattributes(current_date as bar), 'cont', 'ent');
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xmlelement
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-------------------------------------
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<foo bar="2007-01-26">content</foo>
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]]></screen>
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</para>
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<para>
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Element and attribute names that are not valid XML names are
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escaped by replacing the offending characters by the sequence
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<literal>_x<replaceable>HHHH</replaceable>_</literal>, where
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<replaceable>HHHH</replaceable> is the character's Unicode
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codepoint in hexadecimal notation. For example:
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<screen><![CDATA[
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SELECT xmlelement(name "foo$bar", xmlattributes('xyz' as "a&b"));
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xmlelement
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----------------------------------
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<foo_x0024_bar a_x0026_b="xyz"/>
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]]></screen>
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</para>
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<para>
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An explicit attribute name need not be specified if the attribute
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value is a column reference, in which case the column's name will
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be used as attribute name by default. In any other case, the
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attribute must be given an explicit name. So this example is
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valid:
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<screen>
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CREATE TABLE test (a xml, b xml);
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SELECT xmlelement(name test, xmlattributes(a, b)) FROM test;
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</screen>
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But these are not:
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<screen>
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SELECT xmlelement(name test, xmlattributes('constant'), a, b) FROM test;
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SELECT xmlelement(name test, xmlattributes(func(a, b))) FROM test;
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</screen>
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</para>
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<para>
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Element content, if specified, will be formatted according to
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data type. If the content is itself of type <type>xml</type>,
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complex XML documents can be constructed. For example:
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<screen><![CDATA[
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SELECT xmlelement(name foo, xmlattributes('xyz' as bar),
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xmlelement(name abc),
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xmlcomment('test'),
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xmlelement(name xyz));
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xmlelement
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----------------------------------------------
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<foo bar="xyz"><abc/><!--test--><xyz/></foo>
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]]></screen>
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Content of other types will be formatted into valid XML character
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data. This means in particular that the characters <, >,
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and & will be converted to entities. Binary data (data type
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<type>bytea</type>) will be represented in base64 or hex
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encoding, depending on the setting of the configuration parameter
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<xref linkend="guc-xmlbinary">. The particular behavior for
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individual data types is expected evolve in order to align the
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SQL and PostgreSQL data types with the XML Schema specification,
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at which point a more precise description will appear.
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</para>
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</sect3>
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<sect2>
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<sect3>
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<title><literal>xmlforest</literal></title>
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<indexterm>
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@ -10818,16 +10968,54 @@ SELECT (pg_stat_file('filename')).modification;
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</indexterm>
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<synopsis>
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<function>xmlforest</function>(<replaceable>value</replaceable> <optional>AS <replaceable>label</replaceable></optional><optional>, ...</optional>)
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<function>xmlforest</function>(<replaceable>content</replaceable> <optional>AS <replaceable>name</replaceable></optional> <optional>, ...</optional>)
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</synopsis>
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<para>
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Creates XML elements from columns, using the name of each
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column as the name of the corresponding element.
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The <function>xmlforest</function> expression produces an XML
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forest (sequence) of elements using the given names and content.
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</para>
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</sect2>
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<para>
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Examples:
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<screen><![CDATA[
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SELECT xmlforest('abc' AS foo, 123 AS bar);
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xmlforest
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------------------------------
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<foo>abc</foo><bar>123</bar>
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SELECT xmlforest(table_name, column_name) FROM information_schema.columns WHERE table_schema = 'pg_catalog';
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xmlforest
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-------------------------------------------------------------------------------------------
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<table_name>pg_authid</table_name><column_name>rolname</column_name>
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<table_name>pg_authid</table_name><column_name>rolsuper</column_name>
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...
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]]></screen>
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As seen in the second example, the element name can be omitted if
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the content value is a column reference, in which case the column
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name is used by default. Otherwise, a name must be specified.
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</para>
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<para>
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Element names that are not valid XML names are escaped as shown
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for <function>xmlelement</function> above. Similarly, content
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data is escaped to make valid XML content, unless it is already
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of type <type>xml</type>.
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</para>
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<para>
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Note that XML forests are not valid XML documents if they consist
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of more than one element. So it might be useful to wrap
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<function>xmlforest</function> expressions in
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<function>xmlelement</function>.
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</para>
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</sect3>
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<sect2>
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<sect3>
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<title><literal>xmlpi</literal></title>
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<indexterm>
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@ -10839,11 +11027,24 @@ SELECT (pg_stat_file('filename')).modification;
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</synopsis>
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<para>
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Creates an XML processing instruction.
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The <function>xmlpi</function> expression creates an XML
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processing instruction. The content, if present, must not
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contain the character sequence <literal>?<</literal>.
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</para>
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</sect2>
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<para>
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Example:
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<screen><![CDATA[
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SELECT xmlpi(name php, 'echo "hello world";');
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xmlpi
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-----------------------------
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<?php echo "hello world";?>
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]]></screen>
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</para>
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||||
</sect3>
|
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<sect2>
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<sect3>
|
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<title><literal>xmlroot</literal></title>
|
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<indexterm>
|
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@ -10851,13 +11052,132 @@ SELECT (pg_stat_file('filename')).modification;
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</indexterm>
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<synopsis>
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<function>xmlroot</function>(<replaceable>xml</replaceable>, version <replaceable>text</replaceable> <optional>, standalone yes|no|no value</optional>)
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<function>xmlroot</function>(<replaceable>xml</replaceable>, version <replaceable>text</replaceable>|no value <optional>, standalone yes|no|no value</optional>)
|
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</synopsis>
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<para>
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Creates the root node of an XML document.
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The <function>xmlroot</function> expression alters the properties
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of the root node of an XML value. If a version is specified,
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this replaces the value in the version declaration, if a
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standalone value is specified, this replaces the value in the
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standalone declaration.
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</para>
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<para>
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<screen><![CDATA[
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SELECT xmlroot(xmlparse(document '<?xml version="1.1"?><content>abc</content>'), version '1.0', standalone yes);
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|
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xmlroot
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----------------------------------------
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<?xml version="1.0" standalone="yes"?>
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<content>abc</content>
|
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]]></screen>
|
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</para>
|
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</sect3>
|
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|
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<sect3>
|
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<title>XML Predicates</title>
|
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|
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<indexterm>
|
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<primary>IS DOCUMENT</primary>
|
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</indexterm>
|
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|
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<synopsis>
|
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<replaceable>xml</replaceable> IS DOCUMENT
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</synopsis>
|
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|
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<para>
|
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The expression <literal>IS DOCUMENT</literal> returns true if the
|
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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
|
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null. See <xref linkend="datatype-xml"> about the difference
|
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between documents and content fragments.
|
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</para>
|
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</sect3>
|
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</sect2>
|
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|
||||
<sect2>
|
||||
<title>Processing XML</title>
|
||||
|
||||
<para>
|
||||
<acronym>XML</> support is not just the existence of an
|
||||
<type>xml</type> data type, but a variety of features supported by
|
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a database system. These capabilities include import/export,
|
||||
indexing, searching, transforming, and <acronym>XML</> to
|
||||
<acronym>SQL</> mapping. <productname>PostgreSQL</> supports some
|
||||
but not all of these <acronym>XML</> capabilities. For an
|
||||
overview of <acronym>XML</> use in databases, see <ulink
|
||||
url="http://www.rpbourret.com/xml/XMLAndDatabases.htm"></>.
|
||||
</para>
|
||||
|
||||
<variablelist>
|
||||
<varlistentry>
|
||||
<term>Import/Export</term>
|
||||
<listitem>
|
||||
|
||||
<para>
|
||||
There is no facility for mapping <acronym>XML</> to relational
|
||||
tables. An external tool must be used for this. One simple way
|
||||
to export <acronym>XML</> is to use <application>psql</> in
|
||||
<acronym>HTML</> mode (<literal>\pset format html</>), and
|
||||
convert the <acronym>XHTML</> output to XML using an external
|
||||
tool.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term>Indexing</term>
|
||||
<listitem>
|
||||
|
||||
<para>
|
||||
<filename>contrib/xml2/</> functions can be used in expression
|
||||
indexes to index specific <acronym>XML</> fields. To index the
|
||||
full contents of <acronym>XML</> documents, the full-text
|
||||
indexing tool <filename>contrib/tsearch2/</> can be used. Of
|
||||
course, Tsearch2 indexes have no <acronym>XML</> awareness so
|
||||
additional <filename>contrib/xml2/</> checks should be added to
|
||||
queries.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term>Searching</term>
|
||||
<listitem>
|
||||
|
||||
<para>
|
||||
XPath searches are implemented using <filename>contrib/xml2/</>.
|
||||
It processes <acronym>XML</> text documents and returns results
|
||||
based on the requested query.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term>Transforming</term>
|
||||
<listitem>
|
||||
|
||||
<para>
|
||||
<filename>contrib/xml2/</> supports <acronym>XSLT</> (Extensible
|
||||
Stylesheet Language Transformation).
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term>XML to SQL Mapping</term>
|
||||
<listitem>
|
||||
|
||||
<para>
|
||||
This involves converting <acronym>XML</> data to and from
|
||||
relational structures. <productname>PostgreSQL</> has no
|
||||
internal support for such mapping, and relies on external tools
|
||||
to do such conversions.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
</variablelist>
|
||||
</sect2>
|
||||
|
||||
</sect1>
|
||||
</chapter>
|
||||
|
||||
Loading…
Reference in New Issue
Block a user