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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_foreign_data_wrapper.sgml,v 1.1 2008/12/19 16:25:16 petere Exp $
PostgreSQL documentation
-->
<refentry id="SQL-CREATEFOREIGNDATAWRAPPER">
<refmeta>
<refentrytitle id="sql-createforeigndatawrapper-title">CREATE FOREIGN DATA WRAPPER</refentrytitle>
<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>
LIBRARY '<replaceable class="parameter">libraryname</replaceable>'
LANGUAGE C
[ 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><replaceable class="parameter">libraryname</replaceable></term>
<listitem>
<para>
The name of the shared library implementing the foreign-data
wrapper. The file name is specified in the same way as for
shared library names in <xref linkend="sql-createfunction"
endterm="sql-createfunction-title">; in particular, one can rely
on a search path and automatic addition of the system's standard
shared library file name extension.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>LANGUAGE C</literal></term>
<listitem>
<para>
Currently, only the C programming language is supported for
implementing foreign-data wrappers.
</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.
The functionality to actually query external data does not exist
yet.
</para>
<para>
The C language API for foreign-data wrappers is currently not
documented, stable, or complete. Would-be authors of functionality
interfacing with the SQL/MED functionality are advised to contact
the PostgreSQL developers.
</para>
<para>
There are currently two foreign-data wrapper libraries
provided: <filename>dummy_fdw</filename>, which does nothing and
could be useful for testing,
and <filename>postgresql_fdw</filename>, which accepts options
corresponding to <application>libpq</> connection parameters.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Create a foreign-data wrapper <literal>dummy</> with
library <literal>dummy_fdw</>:
<programlisting>
CREATE FOREIGN DATA WRAPPER dummy LIBRARY 'dummy_fdw' LANGUAGE C;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>postgresql</> with
library <literal>postgresql_fdw</>:
<programlisting>
CREATE FOREIGN DATA WRAPPER postgresql LIBRARY 'postgresql_fdw' LANGUAGE C;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>mywrapper</> with library
<literal>/home/bob/mywrapper.so</> and some options:
<programlisting>
CREATE FOREIGN DATA WRAPPER mywrapper
LIBRARY '/home/bob/mywrapper.so'
LANGUAGE C
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>LIBRARY</literal> clause is not optional 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>
|
