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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_foreign_data_wrapper.sgml,v 1.6 2009/12/23 12:23:58 heikki Exp $
PostgreSQL documentation
-->
<refentry id="SQL-CREATEFOREIGNDATAWRAPPER">
<refmeta>
<refentrytitle id="sql-createforeigndatawrapper-title">CREATE FOREIGN DATA WRAPPER</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>CREATE FOREIGN DATA WRAPPER</refname>
<refpurpose>define a new foreign-data wrapper</refpurpose>
</refnamediv>
<indexterm zone="sql-createforeigndatawrapper">
<primary>CREATE FOREIGN DATA WRAPPER</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
CREATE FOREIGN DATA WRAPPER <replaceable class="parameter">name</replaceable>
[ VALIDATOR <replaceable class="parameter">valfunction</replaceable> | NO VALIDATOR ]
[ OPTIONS ( <replaceable class="PARAMETER">option</replaceable> '<replaceable class="PARAMETER">value</replaceable>' [, ... ] ) ]
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>CREATE FOREIGN DATA WRAPPER</command> creates a new
foreign-data wrapper. The user who defines a foreign-data wrapper
becomes its owner.
</para>
<para>
The foreign-data wrapper name must be unique within the database.
</para>
<para>
Only superusers can create foreign-data wrappers.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
The name of the foreign-data wrapper to be created.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>VALIDATOR <replaceable class="parameter">valfunction</replaceable></literal></term>
<listitem>
<para>
<replaceable class="parameter">valfunction</replaceable> is the
name of a previously registered function that will be called to
check the generic options given to the foreign-data wrapper, as
well as to foreign servers and user mappings using the
foreign-data wrapper. If no validator function or <literal>NO
VALIDATOR</literal> is specified, then options will not be
checked at creation time. (Foreign-data wrappers will possibly
ignore or reject invalid option specifications at run time,
depending on the implementation.) The validator function must
take two arguments: one of type <type>text[]</type>, which will
contain the array of options as stored in the system catalogs,
and one of type <type>oid</type>, which will be the OID of the
system catalog containing the options. The return type is ignored;
the function should indicate invalid options using the
<function>ereport()</function> function.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>OPTIONS ( <replaceable class="PARAMETER">option</replaceable> '<replaceable class="PARAMETER">value</replaceable>' [, ... ] )</literal></term>
<listitem>
<para>
This clause specifies options for the new foreign-data wrapper.
The allowed option names and values are specific to each foreign
data wrapper and are validated using the foreign-data wrapper
library. Option names must be unique.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
At the moment, the foreign-data wrapper functionality is very
rudimentary. The purpose of foreign-data wrappers, foreign
servers, and user mappings is to store this information in a
standard way so that it can be queried by interested applications.
One such application is <application>dblink</application>;
see <xref linkend="dblink">. The functionality to actually query
external data through a foreign-data wrapper library does not exist
yet.
</para>
<para>
There is currently one foreign-data wrapper validator function
provided:
<filename>postgresql_fdw_validator</filename>, which accepts
options corresponding to <application>libpq</> connection
parameters.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Create a foreign-data wrapper <literal>dummy</>:
<programlisting>
CREATE FOREIGN DATA WRAPPER dummy;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>postgresql</> with
validator function <literal>postgresql_fdw_validator</>:
<programlisting>
CREATE FOREIGN DATA WRAPPER postgresql VALIDATOR postgresql_fdw_validator;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>mywrapper</> with some
options:
<programlisting>
CREATE FOREIGN DATA WRAPPER mywrapper
OPTIONS (debug 'true');
</programlisting>
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
<command>CREATE FOREIGN DATA WRAPPER</command> conforms to ISO/IEC
9075-9 (SQL/MED), with the exception that
the <literal>VALIDATOR</literal> clause is an extension and the
clauses <literal>LIBRARY</literal> and <literal>LANGUAGE</literal>
are not yet implemented in PostgreSQL.
</para>
<para>
Note, however, that the SQL/MED functionality as a whole is not yet
conforming.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-alterforeigndatawrapper" endterm="sql-alterforeigndatawrapper-title"></member>
<member><xref linkend="sql-dropforeigndatawrapper" endterm="sql-dropforeigndatawrapper-title"></member>
<member><xref linkend="sql-createserver" endterm="sql-createserver-title"></member>
<member><xref linkend="sql-createusermapping" endterm="sql-createusermapping-title"></member>
</simplelist>
</refsect1>
</refentry>
|
