<!-- doc/src/sgml/file-fdw.sgml -->

<sect1 id="file-fdw" xreflabel="file_fdw">
 <title>file_fdw</title>

 <indexterm zone="file-fdw">
  <primary>file_fdw</primary>
 </indexterm>

 <para>
  The <filename>file_fdw</> module provides the foreign-data wrapper
  <function>file_fdw</function>, which can be used to access data
  files in the server's file system.  Data files must be in a format
  that can be read by <command>COPY FROM</command>;
  see <xref linkend="sql-copy"> for details.
 </para>

 <para>
  A foreign table created using this wrapper can have the following options:
 </para>

 <variablelist>

  <varlistentry>
   <term><literal>filename</literal></term>

   <listitem>
    <para>
     Specifies the file to be read.  Required.  Must be an absolute path name.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>format</literal></term>

   <listitem>
    <para>
     Specifies the file's format,
     the same as <command>COPY</>'s <literal>FORMAT</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>header</literal></term>

   <listitem>
    <para>
     Specifies whether the file has a header line,
     the same as <command>COPY</>'s <literal>HEADER</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>delimiter</literal></term>

   <listitem>
    <para>
     Specifies the file's delimiter character,
     the same as <command>COPY</>'s <literal>DELIMITER</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>quote</literal></term>

   <listitem>
    <para>
     Specifies the file's quote character,
     the same as <command>COPY</>'s <literal>QUOTE</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>escape</literal></term>

   <listitem>
    <para>
     Specifies the file's escape character,
     the same as <command>COPY</>'s <literal>ESCAPE</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>null</literal></term>

   <listitem>
    <para>
     Specifies the file's null string,
     the same as <command>COPY</>'s <literal>NULL</literal> option.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term><literal>encoding</literal></term>

   <listitem>
    <para>
     Specifies the file's encoding.
     the same as <command>COPY</>'s <literal>ENCODING</literal> option.
    </para>
   </listitem>
  </varlistentry>

 </variablelist>

 <para>
  A column of a foreign table created using this wrapper can have the
  following options:
 </para>

 <variablelist>

  <varlistentry>
   <term><literal>force_not_null</literal></term>

   <listitem>
    <para>
     This is a boolean option.  If true, it specifies that values of the
     column should not be matched against the null string (that is, the
     file-level <literal>null</literal> option).  This has the same effect
     as listing the column in <command>COPY</>'s
     <literal>FORCE_NOT_NULL</literal> option.
    </para>
   </listitem>
  </varlistentry>

 </variablelist>

 <para>
  <command>COPY</>'s <literal>OIDS</literal> and
  <literal>FORCE_QUOTE</literal> options are currently not supported by
  <literal>file_fdw</>.
 </para>

 <para>
  These options can only be specified for a foreign table or its columns, not
  in the options of the <literal>file_fdw</> foreign-data wrapper, nor in the
  options of a server or user mapping using the wrapper.
 </para>

 <para>
  Changing table-level options requires superuser privileges, for security
  reasons: only a superuser should be able to determine which file is read.
  In principle non-superusers could be allowed to change the other options,
  but that's not supported at present.
 </para>

 <para>
  For a foreign table using <literal>file_fdw</>, <command>EXPLAIN</> shows
  the name of the file to be read.  Unless <literal>COSTS OFF</> is
  specified, the file size (in bytes) is shown as well.
 </para>

</sect1>
