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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>CREATE FOREIGN DATA WRAPPER</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-createextension.html" title="CREATE EXTENSION" /><link rel="next" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE FOREIGN DATA WRAPPER</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createextension.html" title="CREATE EXTENSION">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-CREATEFOREIGNDATAWRAPPER"><div class="titlepage"></div><a id="id-1.9.3.65.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE FOREIGN DATA WRAPPER</span></h2><p>CREATE FOREIGN DATA WRAPPER — define a new foreign-data wrapper</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">3CREATE FOREIGN DATA WRAPPER <em class="replaceable"><code>name</code></em>4    [ HANDLER <em class="replaceable"><code>handler_function</code></em> | NO HANDLER ]5    [ VALIDATOR <em class="replaceable"><code>validator_function</code></em> | NO VALIDATOR ]6    [ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]7</pre></div><div class="refsect1" id="id-1.9.3.65.5"><h2>Description</h2><p>8   <code class="command">CREATE FOREIGN DATA WRAPPER</code> creates a new9   foreign-data wrapper.  The user who defines a foreign-data wrapper10   becomes its owner.11  </p><p>12   The foreign-data wrapper name must be unique within the database.13  </p><p>14   Only superusers can create foreign-data wrappers.15  </p></div><div class="refsect1" id="id-1.9.3.65.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>16      The name of the foreign-data wrapper to be created.17     </p></dd><dt><span class="term"><code class="literal">HANDLER <em class="replaceable"><code>handler_function</code></em></code></span></dt><dd><p><em class="replaceable"><code>handler_function</code></em> is the18      name of a previously registered function that will be called to19      retrieve the execution functions for foreign tables.20      The handler function must take no arguments, and21      its return type must be <code class="type">fdw_handler</code>.22     </p><p>23      It is possible to create a foreign-data wrapper with no handler24      function, but foreign tables using such a wrapper can only be declared,25      not accessed.26     </p></dd><dt><span class="term"><code class="literal">VALIDATOR <em class="replaceable"><code>validator_function</code></em></code></span></dt><dd><p><em class="replaceable"><code>validator_function</code></em>27      is the name of a previously registered function that will be called to28      check the generic options given to the foreign-data wrapper, as29      well as options for foreign servers, user mappings and foreign tables30      using the foreign-data wrapper.  If no validator function or <code class="literal">NO31      VALIDATOR</code> is specified, then options will not be32      checked at creation time.  (Foreign-data wrappers will possibly33      ignore or reject invalid option specifications at run time,34      depending on the implementation.)  The validator function must35      take two arguments: one of type <code class="type">text[]</code>, which will36      contain the array of options as stored in the system catalogs,37      and one of type <code class="type">oid</code>, which will be the OID of the38      system catalog containing the options. The return type is ignored;39      the function should report invalid options using the40      <code class="function">ereport(ERROR)</code> function.41     </p></dd><dt><span class="term"><code class="literal">OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] )</code></span></dt><dd><p>42      This clause specifies options for the new foreign-data wrapper.43      The allowed option names and values are specific to each foreign44      data wrapper and are validated using the foreign-data wrapper's45      validator function.  Option names must be unique.46     </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.65.7"><h2>Notes</h2><p>47   <span class="productname">PostgreSQL</span>'s foreign-data functionality is still under48   active development.  Optimization of queries is primitive (and mostly left49   to the wrapper, too).  Thus, there is considerable room for future50   performance improvements.51  </p></div><div class="refsect1" id="id-1.9.3.65.8"><h2>Examples</h2><p>52   Create a useless foreign-data wrapper <code class="literal">dummy</code>:53</p><pre class="programlisting">54CREATE FOREIGN DATA WRAPPER dummy;55</pre><p>56  </p><p>57   Create a foreign-data wrapper <code class="literal">file</code> with58   handler function <code class="literal">file_fdw_handler</code>:59</p><pre class="programlisting">60CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;61</pre><p>62  </p><p>63   Create a foreign-data wrapper <code class="literal">mywrapper</code> with some64   options:65</p><pre class="programlisting">66CREATE FOREIGN DATA WRAPPER mywrapper67    OPTIONS (debug 'true');68</pre></div><div class="refsect1" id="id-1.9.3.65.9"><h2>Compatibility</h2><p>69   <code class="command">CREATE FOREIGN DATA WRAPPER</code> conforms to ISO/IEC70   9075-9 (SQL/MED), with the exception that the <code class="literal">HANDLER</code>71   and <code class="literal">VALIDATOR</code> clauses are extensions and the standard72   clauses <code class="literal">LIBRARY</code> and <code class="literal">LANGUAGE</code>73   are not implemented in <span class="productname">PostgreSQL</span>.74  </p><p>75   Note, however, that the SQL/MED functionality as a whole is not yet76   conforming.77  </p></div><div class="refsect1" id="id-1.9.3.65.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-alterforeigndatawrapper.html" title="ALTER FOREIGN DATA WRAPPER"><span class="refentrytitle">ALTER FOREIGN DATA WRAPPER</span></a>, <a class="xref" href="sql-dropforeigndatawrapper.html" title="DROP FOREIGN DATA WRAPPER"><span class="refentrytitle">DROP FOREIGN DATA WRAPPER</span></a>, <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>, <a class="xref" href="sql-createusermapping.html" title="CREATE USER MAPPING"><span class="refentrytitle">CREATE USER MAPPING</span></a>, <a class="xref" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE"><span class="refentrytitle">CREATE FOREIGN TABLE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createextension.html" title="CREATE EXTENSION">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createforeigntable.html" title="CREATE FOREIGN TABLE">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE EXTENSION </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> CREATE FOREIGN TABLE</td></tr></table></div></body></html>