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Add xmlexists function

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by Mike Fowler, reviewed by Peter Eisentraut
This commit is contained in:
Peter Eisentraut
2010-08-05 04:21:54 +00:00
parent 26e47efb66
commit 641459f269
10 changed files with 312 additions and 31 deletions
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55
doc/src/sgml/func.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.522 2010/07/29 19:34:40 petere Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.523 2010/08/05 04:21:53 petere Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -8554,9 +8554,18 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
]]></screen>
</para>
</sect3>
</sect2>
<sect2>
<title>XML Predicates</title>
<para>
The expressions described in this section check properties
of <type>xml</type> values.
</para>
<sect3>
<title>XML Predicates</title>
<title>IS DOCUMENT</title>
<indexterm>
<primary>IS DOCUMENT</primary>
@ -8574,6 +8583,48 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
between documents and content fragments.
</para>
</sect3>
<sect3>
<title>XMLEXISTS</title>
<indexterm>
<primary>XMLEXISTS</primary>
</indexterm>
<synopsis>
<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY REF</optional> <replaceable>xml</replaceable> <optional>BY REF</optional>)
</synopsis>
<para>
The function <function>xmlexists</function> returns true if the
XPath expression in the first argument returns any nodes, and
false otherwise. (If either argument is null, the result is
null.)
</para>
<para>
Example:
<screen><![CDATA[
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Toronto</town><town>Ottawa</town></towns>');
xmlexists
------------
t
(1 row)
]]></screen>
</para>
<para>
The <literal>BY REF</literal> clauses have no effect in
PostgreSQL, but are allowed for SQL conformance and compatibility
with other implementations. Per SQL standard, the
first <literal>BY REF</literal> is required, the second is
optional. Also note that the SQL standard specifies
the <function>xmlexists</function> construct to take an XQuery
expression as first argument, but PostgreSQL currently only
supports XPath, which is a subset of XQuery.
</para>
</sect3>
</sect2>
<sect2 id="functions-xml-processing">