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<!--
doc/src/sgml/ref/create_foreign_data_wrapper.sgml
PostgreSQL documentation
-->
<refentry id="sql-createforeigndatawrapper">
<indexterm zone="sql-createforeigndatawrapper">
<primary>CREATE FOREIGN DATA WRAPPER</primary>
</indexterm>
<refmeta>
<refentrytitle>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>
<refsynopsisdiv>
<synopsis>
CREATE FOREIGN DATA WRAPPER <replaceable class="parameter">name</replaceable>
[ HANDLER <replaceable class="parameter">handler_function</replaceable> | NO HANDLER ]
[ VALIDATOR <replaceable class="parameter">validator_function</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>HANDLER <replaceable class="parameter">handler_function</replaceable></literal></term>
<listitem>
<para><replaceable class="parameter">handler_function</replaceable> is the
name of a previously registered function that will be called to
retrieve the execution functions for foreign tables.
The handler function must take no arguments, and
its return type must be <type>fdw_handler</type>.
</para>
<para>
It is possible to create a foreign-data wrapper with no handler
function, but foreign tables using such a wrapper can only be declared,
not accessed.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>VALIDATOR <replaceable class="parameter">validator_function</replaceable></literal></term>
<listitem>
<para><replaceable class="parameter">validator_function</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 options for foreign servers, user mappings and foreign tables
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 report invalid options using the
<function>ereport(ERROR)</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's
validator function. Option names must be unique.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
<productname>PostgreSQL</productname>'s foreign-data functionality is still under
active development. Optimization of queries is primitive (and mostly left
to the wrapper, too). Thus, there is considerable room for future
performance improvements.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Create a useless foreign-data wrapper <literal>dummy</literal>:
<programlisting>
CREATE FOREIGN DATA WRAPPER dummy;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>file</literal> with
handler function <literal>file_fdw_handler</literal>:
<programlisting>
CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;
</programlisting>
</para>
<para>
Create a foreign-data wrapper <literal>mywrapper</literal> 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>HANDLER</literal>
and <literal>VALIDATOR</literal> clauses are extensions and the standard
clauses <literal>LIBRARY</literal> and <literal>LANGUAGE</literal>
are not implemented in <productname>PostgreSQL</productname>.
</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"/></member>
<member><xref linkend="sql-dropforeigndatawrapper"/></member>
<member><xref linkend="sql-createserver"/></member>
<member><xref linkend="sql-createusermapping"/></member>
<member><xref linkend="sql-createforeigntable"/></member>
</simplelist>
</refsect1>
</refentry>
|
