Doc: Fix various inconsistencies

[postgresql] / doc / src / sgml / ref / copy.sgml

<!--
doc/src/sgml/ref/copy.sgml
PostgreSQL documentation
-->


<refentry id="sql-copy">
 <indexterm zone="sql-copy">
  <primary>COPY</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>COPY</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>COPY</refname>
  <refpurpose>copy data between a file and a table</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
COPY <replaceable class="parameter">table_name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
    FROM { '<replaceable class="parameter">filename</replaceable>' | PROGRAM '<replaceable class="parameter">command</replaceable>' | STDIN }
    [ [ WITH ] ( <replaceable class="parameter">option</replaceable> [, ...] ) ]
    [ WHERE <replaceable class="parameter">condition</replaceable> ]

COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ] | ( <replaceable class="parameter">query</replaceable> ) }
    TO { '<replaceable class="parameter">filename</replaceable>' | PROGRAM '<replaceable class="parameter">command</replaceable>' | STDOUT }
    [ [ WITH ] ( <replaceable class="parameter">option</replaceable> [, ...] ) ]

<phrase>where <replaceable class="parameter">option</replaceable> can be one of:</phrase>

    FORMAT <replaceable class="parameter">format_name</replaceable>
    FREEZE [ <replaceable class="parameter">boolean</replaceable> ]
    DELIMITER '<replaceable class="parameter">delimiter_character</replaceable>'
    NULL '<replaceable class="parameter">null_string</replaceable>'
    HEADER [ <replaceable class="parameter">boolean</replaceable> ]
    QUOTE '<replaceable class="parameter">quote_character</replaceable>'
    ESCAPE '<replaceable class="parameter">escape_character</replaceable>'
    FORCE_QUOTE { ( <replaceable class="parameter">column_name</replaceable> [, ...] ) | * }
    FORCE_NOT_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
    FORCE_NULL ( <replaceable class="parameter">column_name</replaceable> [, ...] )
    ENCODING '<replaceable class="parameter">encoding_name</replaceable>'
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>COPY</command> moves data between
   <productname>PostgreSQL</productname> tables and standard file-system
   files. <command>COPY TO</command> copies the contents of a table
   <emphasis>to</emphasis> a file, while <command>COPY FROM</command> copies
   data <emphasis>from</emphasis> a file to a table (appending the data to
   whatever is in the table already).  <command>COPY TO</command>
   can also copy the results of a <command>SELECT</command> query.
  </para>

  <para>
   If a list of columns is specified, <command>COPY</command> will
   only copy the data in the specified columns to or from the file.
   If there are any columns in the table that are not in the column list,
   <command>COPY FROM</command> will insert the default values for
   those columns.
  </para>

  <para>
   <command>COPY</command> with a file name instructs the
   <productname>PostgreSQL</productname> server to directly read from
   or write to a file. The file must be accessible by the
   <productname>PostgreSQL</productname> user (the user ID the server
   runs as) and the name must be specified from the viewpoint of the
   server. When <literal>PROGRAM</literal> is specified, the server
   executes the given command and reads from the standard output of the
   program, or writes to the standard input of the program. The command
   must be specified from the viewpoint of the server, and be executable
   by the <productname>PostgreSQL</productname> user.  When
   <literal>STDIN</literal> or <literal>STDOUT</literal> is
   specified, data is transmitted via the connection between the
   client and the server.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="parameter">table_name</replaceable></term>
    <listitem>
     <para>
      The name (optionally schema-qualified) of an existing table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">column_name</replaceable></term>
     <listitem>
     <para>
      An optional list of columns to be copied.  If no column list is
      specified, all columns of the table except generated columns will be
      copied.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">query</replaceable></term>
    <listitem>
     <para>
      A <xref linkend="sql-select"/>, <xref linkend="sql-values"/>,
      <xref linkend="sql-insert"/>, <xref linkend="sql-update"/> or
      <xref linkend="sql-delete"/> command whose results are to be
      copied.  Note that parentheses are required around the query.
     </para>
     <para>
      For <command>INSERT</command>, <command>UPDATE</command> and
      <command>DELETE</command> queries a RETURNING clause must be provided,
      and the target relation must not have a conditional rule, nor
      an <literal>ALSO</literal> rule, nor an <literal>INSTEAD</literal> rule
      that expands to multiple statements.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">filename</replaceable></term>
    <listitem>
     <para>
      The path name of the input or output file.  An input file name can be
      an absolute or relative path, but an output file name must be an absolute
      path.  Windows users might need to use an <literal>E''</literal> string and
      double any backslashes used in the path name.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>PROGRAM</literal></term>
    <listitem>
     <para>
      A command to execute. In <command>COPY FROM</command>, the input is
      read from standard output of the command, and in <command>COPY TO</command>,
      the output is written to the standard input of the command.
     </para>
     <para>
      Note that the command is invoked by the shell, so if you need to pass
      any arguments to shell command that come from an untrusted source, you
      must be careful to strip or escape any special characters that might
      have a special meaning for the shell. For security reasons, it is best
      to use a fixed command string, or at least avoid passing any user input
      in it.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>STDIN</literal></term>
    <listitem>
     <para>
      Specifies that input comes from the client application.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>STDOUT</literal></term>
    <listitem>
     <para>
      Specifies that output goes to the client application.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><replaceable class="parameter">boolean</replaceable></term>
    <listitem>
     <para>
      Specifies whether the selected option should be turned on or off.
      You can write <literal>TRUE</literal>, <literal>ON</literal>, or
      <literal>1</literal> to enable the option, and <literal>FALSE</literal>,
      <literal>OFF</literal>, or <literal>0</literal> to disable it.  The
      <replaceable class="parameter">boolean</replaceable> value can also
      be omitted, in which case <literal>TRUE</literal> is assumed.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>FORMAT</literal></term>
    <listitem>
     <para>
      Selects the data format to be read or written:
      <literal>text</literal>,
      <literal>csv</literal> (Comma Separated Values),
      or <literal>binary</literal>.
      The default is <literal>text</literal>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>FREEZE</literal></term>
    <listitem>
     <para>
      Requests copying the data with rows already frozen, just as they
      would be after running the <command>VACUUM FREEZE</command> command.
      This is intended as a performance option for initial data loading.
      Rows will be frozen only if the table being loaded has been created
      or truncated in the current subtransaction, there are no cursors
      open and there are no older snapshots held by this transaction.  It is
      currently not possible to perform a <command>COPY FREEZE</command> on
      a partitioned table.
     </para>
     <para>
      Note that all other sessions will immediately be able to see the data
      once it has been successfully loaded. This violates the normal rules
      of MVCC visibility and users specifying should be aware of the
      potential problems this might cause.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DELIMITER</literal></term>
    <listitem>
     <para>
      Specifies the character that separates columns within each row
      (line) of the file.  The default is a tab character in text format,
      a comma in <literal>CSV</literal> format.
      This must be a single one-byte character.
      This option is not allowed when using <literal>binary</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>NULL</literal></term>
    <listitem>
     <para>
      Specifies the string that represents a null value. The default is
      <literal>\N</literal> (backslash-N) in text format, and an unquoted empty
      string in <literal>CSV</literal> format. You might prefer an
      empty string even in text format for cases where you don't want to
      distinguish nulls from empty strings.
      This option is not allowed when using <literal>binary</literal> format.
     </para>

     <note>
      <para>
       When using <command>COPY FROM</command>, any data item that matches
       this string will be stored as a null value, so you should make
       sure that you use the same string as you used with
       <command>COPY TO</command>.
      </para>
     </note>

    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>HEADER</literal></term>
    <listitem>
     <para>
      Specifies that the file contains a header line with the names of each
      column in the file.  On output, the first line contains the column
      names from the table, and on input, the first line is ignored.
      This option is allowed only when using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>QUOTE</literal></term>
    <listitem>
     <para>
      Specifies the quoting character to be used when a data value is quoted.
      The default is double-quote.
      This must be a single one-byte character.
      This option is allowed only when using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ESCAPE</literal></term>
    <listitem>
     <para>
      Specifies the character that should appear before a
      data character that matches the <literal>QUOTE</literal> value.
      The default is the same as the <literal>QUOTE</literal> value (so that
      the quoting character is doubled if it appears in the data).
      This must be a single one-byte character.
      This option is allowed only when using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>FORCE_QUOTE</literal></term>
    <listitem>
     <para>
      Forces quoting to be
      used for all non-<literal>NULL</literal> values in each specified column.
      <literal>NULL</literal> output is never quoted. If <literal>*</literal> is specified,
      non-<literal>NULL</literal> values will be quoted in all columns.
      This option is allowed only in <command>COPY TO</command>, and only when
      using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>FORCE_NOT_NULL</literal></term>
    <listitem>
     <para>
      Do not match the specified columns' values against the null string.
      In the default case where the null string is empty, this means that
      empty values will be read as zero-length strings rather than nulls,
      even when they are not quoted.
      This option is allowed only in <command>COPY FROM</command>, and only when
      using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>FORCE_NULL</literal></term>
    <listitem>
     <para>
      Match the specified columns' values against the null string, even
      if it has been quoted, and if a match is found set the value to
      <literal>NULL</literal>. In the default case where the null string is empty,
      this converts a quoted empty string into NULL.
      This option is allowed only in <command>COPY FROM</command>, and only when
      using <literal>CSV</literal> format.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ENCODING</literal></term>
    <listitem>
     <para>
      Specifies that the file is encoded in the <replaceable
      class="parameter">encoding_name</replaceable>.  If this option is
      omitted, the current client encoding is used. See the Notes below
      for more details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>WHERE</literal></term>
    <listitem>
   <para>
    The optional <literal>WHERE</literal> clause has the general form
<synopsis>
WHERE <replaceable class="parameter">condition</replaceable>
</synopsis>
    where <replaceable class="parameter">condition</replaceable> is
    any expression that evaluates to a result of type
    <type>boolean</type>.  Any row that does not satisfy this
    condition will not be inserted to the table.  A row satisfies the
    condition if it returns true when the actual row values are
    substituted for any variable references.
   </para>

   <para>
    Currently, subqueries are not allowed in <literal>WHERE</literal>
    expressions, and the evaluation does not see any changes made by the
    <command>COPY</command> itself (this matters when the expression
    contains calls to <literal>VOLATILE</literal> functions).
   </para>

    </listitem>
   </varlistentry>

  </variablelist>
 </refsect1>

 <refsect1>
  <title>Outputs</title>

  <para>
   On successful completion, a <command>COPY</command> command returns a command
   tag of the form
<screen>
COPY <replaceable class="parameter">count</replaceable>
</screen>
   The <replaceable class="parameter">count</replaceable> is the number
   of rows copied.
  </para>

  <note>
   <para>
    <application>psql</application> will print this command tag only if the command
    was not <literal>COPY ... TO STDOUT</literal>, or the
    equivalent <application>psql</application> meta-command
    <literal>\copy ... to stdout</literal>.  This is to prevent confusing the
    command tag with the data that was just printed.
   </para>
  </note>
 </refsect1>

 <refsect1>
  <title>Notes</title>

   <para>
    <command>COPY TO</command> can only be used with plain tables, not
    with views.  However, you can write <literal>COPY (SELECT * FROM
    <replaceable class="parameter">viewname</replaceable>) TO ...</literal>
    to copy the current contents of a view.
   </para>

   <para>
    <command>COPY FROM</command> can be used with plain, foreign, or
    partitioned tables or with views that have
    <literal>INSTEAD OF INSERT</literal> triggers.
   </para>

   <para>
    <command>COPY</command> only deals with the specific table named;
    it does not copy data to or from child tables.  Thus for example
    <literal>COPY <replaceable class="parameter">table</replaceable> TO</literal>
    shows the same data as <literal>SELECT * FROM ONLY <replaceable
    class="parameter">table</replaceable></literal>.  But <literal>COPY
    (SELECT * FROM <replaceable class="parameter">table</replaceable>) TO ...</literal>
    can be used to dump all of the data in an inheritance hierarchy.
   </para>

   <para>
    You must have select privilege on the table
    whose values are read by <command>COPY TO</command>, and
    insert privilege on the table into which values
    are inserted by <command>COPY FROM</command>.  It is sufficient
    to have column privileges on the column(s) listed in the command.
   </para>

   <para>
    If row-level security is enabled for the table, the relevant
    <command>SELECT</command> policies will apply to <literal>COPY
    <replaceable class="parameter">table</replaceable> TO</literal> statements.
    Currently, <command>COPY FROM</command> is not supported for tables
    with row-level security. Use equivalent <command>INSERT</command>
    statements instead.
   </para>

   <para>
    Files named in a <command>COPY</command> command are read or written
    directly by the server, not by the client application. Therefore,
    they must reside on or be accessible to the database server machine,
    not the client. They must be accessible to and readable or writable
    by the <productname>PostgreSQL</productname> user (the user ID the
    server runs as), not the client. Similarly,
    the command specified with <literal>PROGRAM</literal> is executed directly
    by the server, not by the client application, must be executable by the
    <productname>PostgreSQL</productname> user.
    <command>COPY</command> naming a file or command is only allowed to
    database superusers or users who are granted one of the default roles
    <literal>pg_read_server_files</literal>,
    <literal>pg_write_server_files</literal>,
    or <literal>pg_execute_server_program</literal>, since it allows reading
    or writing any file or running a program that the server has privileges to
    access.
   </para>

   <para>
    Do not confuse <command>COPY</command> with the
    <application>psql</application> instruction
    <command><link linkend="app-psql-meta-commands-copy">\copy</link></command>. <command>\copy</command> invokes
    <command>COPY FROM STDIN</command> or <command>COPY TO
    STDOUT</command>, and then fetches/stores the data in a file
    accessible to the <application>psql</application> client. Thus,
    file accessibility and access rights depend on the client rather
    than the server when <command>\copy</command> is used.
   </para>

   <para>
    It is recommended that the file name used in <command>COPY</command>
    always be specified as an absolute path. This is enforced by the
    server in the case of <command>COPY TO</command>, but for
    <command>COPY FROM</command> you do have the option of reading from
    a file specified by a relative path. The path will be interpreted
    relative to the working directory of the server process (normally
    the cluster's data directory), not the client's working directory.
   </para>

   <para>
    Executing a command with <literal>PROGRAM</literal> might be restricted
    by the operating system's access control mechanisms, such as SELinux.
   </para>

   <para>
    <command>COPY FROM</command> will invoke any triggers and check
    constraints on the destination table. However, it will not invoke rules.
   </para>

   <para>
    For identity columns, the <command>COPY FROM</command> command will always
    write the column values provided in the input data, like
    the <command>INSERT</command> option <literal>OVERRIDING SYSTEM
    VALUE</literal>.
   </para>

   <para>
    <command>COPY</command> input and output is affected by
    <varname>DateStyle</varname>. To ensure portability to other
    <productname>PostgreSQL</productname> installations that might use
    non-default <varname>DateStyle</varname> settings,
    <varname>DateStyle</varname> should be set to <literal>ISO</literal> before
    using <command>COPY TO</command>.  It is also a good idea to avoid dumping
    data with <varname>IntervalStyle</varname> set to
    <literal>sql_standard</literal>, because negative interval values might be
    misinterpreted by a server that has a different setting for
    <varname>IntervalStyle</varname>.
   </para>

   <para>
    Input data is interpreted according to <literal>ENCODING</literal>
    option or the current client encoding, and output data is encoded
    in <literal>ENCODING</literal> or the current client encoding, even
    if the data does not pass through the client but is read from or
    written to a file directly by the server.
   </para>

   <para>
    <command>COPY</command> stops operation at the first error. This
    should not lead to problems in the event of a <command>COPY
    TO</command>, but the target table will already have received
    earlier rows in a <command>COPY FROM</command>. These rows will not
    be visible or accessible, but they still occupy disk space. This might
    amount to a considerable amount of wasted disk space if the failure
    happened well into a large copy operation. You might wish to invoke
    <command>VACUUM</command> to recover the wasted space.
   </para>

   <para>
    <literal>FORCE_NULL</literal> and <literal>FORCE_NOT_NULL</literal> can be used
    simultaneously on the same column. This results in converting quoted
    null strings to null values and unquoted null strings to empty strings.
   </para>

 </refsect1>

 <refsect1>
  <title>File Formats</title>

  <refsect2>
   <title>Text Format</title>

   <para>
    When the <literal>text</literal> format is used,
    the data read or written is a text file with one line per table row.
    Columns in a row are separated by the delimiter character.
    The column values themselves are strings generated by the
    output function, or acceptable to the input function, of each
    attribute's data type.  The specified null string is used in
    place of columns that are null.
    <command>COPY FROM</command> will raise an error if any line of the
    input file contains more or fewer columns than are expected.
   </para>

   <para>
    End of data can be represented by a single line containing just
    backslash-period (<literal>\.</literal>).  An end-of-data marker is
    not necessary when reading from a file, since the end of file
    serves perfectly well; it is needed only when copying data to or from
    client applications using pre-3.0 client protocol.
   </para>

   <para>
    Backslash characters (<literal>\</literal>) can be used in the
    <command>COPY</command> data to quote data characters that might
    otherwise be taken as row or column delimiters. In particular, the
    following characters <emphasis>must</emphasis> be preceded by a backslash if
    they appear as part of a column value: backslash itself,
    newline, carriage return, and the current delimiter character.
   </para>

   <para>
    The specified null string is sent by <command>COPY TO</command> without
    adding any backslashes; conversely, <command>COPY FROM</command> matches
    the input against the null string before removing backslashes.  Therefore,
    a null string such as <literal>\N</literal> cannot be confused with
    the actual data value <literal>\N</literal> (which would be represented
    as <literal>\\N</literal>).
   </para>

   <para>
    The following special backslash sequences are recognized by
    <command>COPY FROM</command>:

   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>Sequence</entry>
       <entry>Represents</entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry><literal>\b</literal></entry>
       <entry>Backspace (ASCII 8)</entry>
      </row>
      <row>
       <entry><literal>\f</literal></entry>
       <entry>Form feed (ASCII 12)</entry>
      </row>
      <row>
       <entry><literal>\n</literal></entry>
       <entry>Newline (ASCII 10)</entry>
      </row>
      <row>
       <entry><literal>\r</literal></entry>
       <entry>Carriage return (ASCII 13)</entry>
      </row>
      <row>
       <entry><literal>\t</literal></entry>
       <entry>Tab (ASCII 9)</entry>
      </row>
      <row>
       <entry><literal>\v</literal></entry>
       <entry>Vertical tab (ASCII 11)</entry>
      </row>
      <row>
       <entry><literal>\</literal><replaceable>digits</replaceable></entry>
       <entry>Backslash followed by one to three octal digits specifies
       the character with that numeric code</entry>
      </row>
      <row>
       <entry><literal>\x</literal><replaceable>digits</replaceable></entry>
       <entry>Backslash <literal>x</literal> followed by one or two hex digits specifies
       the character with that numeric code</entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>

    Presently, <command>COPY TO</command> will never emit an octal or
    hex-digits backslash sequence, but it does use the other sequences
    listed above for those control characters.
   </para>

   <para>
    Any other backslashed character that is not mentioned in the above table
    will be taken to represent itself.  However, beware of adding backslashes
    unnecessarily, since that might accidentally produce a string matching the
    end-of-data marker (<literal>\.</literal>) or the null string (<literal>\N</literal> by
    default).  These strings will be recognized before any other backslash
    processing is done.
   </para>

   <para>
    It is strongly recommended that applications generating <command>COPY</command> data convert
    data newlines and carriage returns to the <literal>\n</literal> and
    <literal>\r</literal> sequences respectively.  At present it is
    possible to represent a data carriage return by a backslash and carriage
    return, and to represent a data newline by a backslash and newline.
    However, these representations might not be accepted in future releases.
    They are also highly vulnerable to corruption if the <command>COPY</command> file is
    transferred across different machines (for example, from Unix to Windows
    or vice versa).
   </para>

   <para>
    <command>COPY TO</command> will terminate each row with a Unix-style
    newline (<quote><literal>\n</literal></quote>).  Servers running on Microsoft Windows instead
    output carriage return/newline (<quote><literal>\r\n</literal></quote>), but only for
    <command>COPY</command> to a server file; for consistency across platforms,
    <command>COPY TO STDOUT</command> always sends <quote><literal>\n</literal></quote>
    regardless of server platform.
    <command>COPY FROM</command> can handle lines ending with newlines,
    carriage returns, or carriage return/newlines.  To reduce the risk of
    error due to un-backslashed newlines or carriage returns that were
    meant as data, <command>COPY FROM</command> will complain if the line
    endings in the input are not all alike.
   </para>
  </refsect2>

  <refsect2>
   <title>CSV Format</title>

   <para>
    This format option is used for importing and exporting the Comma
    Separated Value (<literal>CSV</literal>) file format used by many other
    programs, such as spreadsheets. Instead of the escaping rules used by
    <productname>PostgreSQL</productname>'s standard text format, it
    produces and recognizes the common CSV escaping mechanism.
   </para>

   <para>
    The values in each record are separated by the <literal>DELIMITER</literal>
    character. If the value contains the delimiter character, the
    <literal>QUOTE</literal> character, the <literal>NULL</literal> string, a carriage
    return, or line feed character, then the whole value is prefixed and
    suffixed by the <literal>QUOTE</literal> character, and any occurrence
    within the value of a <literal>QUOTE</literal> character or the
    <literal>ESCAPE</literal> character is preceded by the escape character.
    You can also use <literal>FORCE_QUOTE</literal> to force quotes when outputting
    non-<literal>NULL</literal> values in specific columns.
   </para>

   <para>
    The <literal>CSV</literal> format has no standard way to distinguish a
    <literal>NULL</literal> value from an empty string.
    <productname>PostgreSQL</productname>'s <command>COPY</command> handles this by quoting.
    A <literal>NULL</literal> is output as the <literal>NULL</literal> parameter string
    and is not quoted, while a non-<literal>NULL</literal> value matching the
    <literal>NULL</literal> parameter string is quoted.  For example, with the
    default settings, a <literal>NULL</literal> is written as an unquoted empty
    string, while an empty string data value is written with double quotes
    (<literal>""</literal>). Reading values follows similar rules. You can
    use <literal>FORCE_NOT_NULL</literal> to prevent <literal>NULL</literal> input
    comparisons for specific columns. You can also use
    <literal>FORCE_NULL</literal> to convert quoted null string data values to
    <literal>NULL</literal>.
   </para>

   <para>
    Because backslash is not a special character in the <literal>CSV</literal>
    format, <literal>\.</literal>, the end-of-data marker, could also appear
    as a data value.  To avoid any misinterpretation, a <literal>\.</literal>
    data value appearing as a lone entry on a line is automatically
    quoted on output, and on input, if quoted, is not interpreted as the
    end-of-data marker.  If you are loading a file created by another
    application that has a single unquoted column and might have a
    value of <literal>\.</literal>, you might need to quote that value in the
    input file.
   </para>

   <note>
    <para>
     In <literal>CSV</literal> format, all characters are significant. A quoted value
     surrounded by white space, or any characters other than
     <literal>DELIMITER</literal>, will include those characters. This can cause
     errors if you import data from a system that pads <literal>CSV</literal>
     lines with white space out to some fixed width. If such a situation
     arises you might need to preprocess the <literal>CSV</literal> file to remove
     the trailing white space, before importing the data into
     <productname>PostgreSQL</productname>.
    </para>
   </note>

   <note>
    <para>
     CSV format will both recognize and produce CSV files with quoted
     values containing embedded carriage returns and line feeds. Thus
     the files are not strictly one line per table row like text-format
     files.
    </para>
   </note>

   <note>
    <para>
     Many programs produce strange and occasionally perverse CSV files,
     so the file format is more a convention than a standard. Thus you
     might encounter some files that cannot be imported using this
     mechanism, and <command>COPY</command> might produce files that other
     programs cannot process.
    </para>
   </note>

  </refsect2>

  <refsect2>
   <title>Binary Format</title>

   <para>
    The <literal>binary</literal> format option causes all data to be
    stored/read as binary format rather than as text.  It is
    somewhat faster than the text and <literal>CSV</literal> formats,
    but a binary-format file is less portable across machine architectures and
    <productname>PostgreSQL</productname> versions.
    Also, the binary format is very data type specific; for example
    it will not work to output binary data from a <type>smallint</type> column
    and read it into an <type>integer</type> column, even though that would work
    fine in text format.
   </para>

   <para>
    The <literal>binary</literal> file format consists
    of a file header, zero or more tuples containing the row data, and
    a file trailer.  Headers and data are in network byte order.
   </para>

   <note>
    <para>
     <productname>PostgreSQL</productname> releases before 7.4 used a
     different binary file format.
    </para>
   </note>

   <refsect3>
    <title>File Header</title>

    <para>
     The file header consists of 15 bytes of fixed fields, followed
     by a variable-length header extension area.  The fixed fields are:

    <variablelist>
     <varlistentry>
      <term>Signature</term>
      <listitem>
       <para>
11-byte sequence <literal>PGCOPY\n\377\r\n\0</literal> &mdash; note that the zero byte
is a required part of the signature.  (The signature is designed to allow
easy identification of files that have been munged by a non-8-bit-clean
transfer.  This signature will be changed by end-of-line-translation
filters, dropped zero bytes, dropped high bits, or parity changes.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Flags field</term>
      <listitem>
       <para>
32-bit integer bit mask to denote important aspects of the file format. Bits
are numbered from 0 (<acronym>LSB</acronym>) to 31 (<acronym>MSB</acronym>).  Note that
this field is stored in network byte order (most significant byte first),
as are all the integer fields used in the file format.  Bits
16-31 are reserved to denote critical file format issues; a reader
should abort if it finds an unexpected bit set in this range. Bits 0-15
are reserved to signal backwards-compatible format issues; a reader
should simply ignore any unexpected bits set in this range. Currently
only one flag bit is defined, and the rest must be zero:
        <variablelist>
         <varlistentry>
          <term>Bit 16</term>
          <listitem>
           <para>
            If 1, OIDs are included in the data; if 0, not. Oid system columns
            are not supported in <productname>PostgreSQL</productname>
            anymore, but the format still contains the indicator.
           </para>
          </listitem>
         </varlistentry>
        </variablelist></para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Header extension area length</term>
      <listitem>
       <para>
32-bit integer, length in bytes of remainder of header, not including self.
Currently, this is zero, and the first tuple follows
immediately.  Future changes to the format might allow additional data
to be present in the header.  A reader should silently skip over any header
extension data it does not know what to do with.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
    </para>

    <para>
The header extension area is envisioned to contain a sequence of
self-identifying chunks.  The flags field is not intended to tell readers
what is in the extension area.  Specific design of header extension contents
is left for a later release.
    </para>

    <para>
     This design allows for both backwards-compatible header additions (add
     header extension chunks, or set low-order flag bits) and
     non-backwards-compatible changes (set high-order flag bits to signal such
     changes, and add supporting data to the extension area if needed).
    </para>
   </refsect3>

   <refsect3>
    <title>Tuples</title>
    <para>
Each tuple begins with a 16-bit integer count of the number of fields in the
tuple.  (Presently, all tuples in a table will have the same count, but that
might not always be true.)  Then, repeated for each field in the tuple, there
is a 32-bit length word followed by that many bytes of field data.  (The
length word does not include itself, and can be zero.)  As a special case,
-1 indicates a NULL field value.  No value bytes follow in the NULL case.
    </para>

    <para>
There is no alignment padding or any other extra data between fields.
    </para>

    <para>
Presently, all data values in a binary-format file are
assumed to be in binary format (format code one).  It is anticipated that a
future extension might add a header field that allows per-column format codes
to be specified.
    </para>

    <para>
To determine the appropriate binary format for the actual tuple data you
should consult the <productname>PostgreSQL</productname> source, in
particular the <function>*send</function> and <function>*recv</function> functions for
each column's data type (typically these functions are found in the
<filename>src/backend/utils/adt/</filename> directory of the source
distribution).
    </para>

    <para>
If OIDs are included in the file, the OID field immediately follows the
field-count word.  It is a normal field except that it's not included in the
field-count.  Note that oid system columns are not supported in current
versions of <productname>PostgreSQL</productname>.
    </para>
   </refsect3>

   <refsect3>
    <title>File Trailer</title>

    <para>
     The file trailer consists of a 16-bit integer word containing -1.  This
     is easily distinguished from a tuple's field-count word.
    </para>

    <para>
     A reader should report an error if a field-count word is neither -1
     nor the expected number of columns.  This provides an extra
     check against somehow getting out of sync with the data.
    </para>
   </refsect3>
  </refsect2>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   The following example copies a table to the client
   using the vertical bar (<literal>|</literal>) as the field delimiter:
<programlisting>
COPY country TO STDOUT (DELIMITER '|');
</programlisting>
  </para>

  <para>
   To copy data from a file into the <literal>country</literal> table:
<programlisting>
COPY country FROM '/usr1/proj/bray/sql/country_data';
</programlisting>
  </para>

  <para>
   To copy into a file just the countries whose names start with 'A':
<programlisting>
COPY (SELECT * FROM country WHERE country_name LIKE 'A%') TO '/usr1/proj/bray/sql/a_list_countries.copy';
</programlisting>
  </para>

  <para>
   To copy into a compressed file, you can pipe the output through an external
   compression program:
<programlisting>
COPY country TO PROGRAM 'gzip > /usr1/proj/bray/sql/country_data.gz';
</programlisting>
  </para>

  <para>
   Here is a sample of data suitable for copying into a table from
   <literal>STDIN</literal>:
<programlisting>
AF      AFGHANISTAN
AL      ALBANIA
DZ      ALGERIA
ZM      ZAMBIA
ZW      ZIMBABWE
</programlisting>
   Note that the white space on each line is actually a tab character.
  </para>

  <para>
   The following is the same data, output in binary format.
   The data is shown after filtering through the
   Unix utility <command>od -c</command>. The table has three columns;
   the first has type <type>char(2)</type>, the second has type <type>text</type>,
   and the third has type <type>integer</type>. All the rows have a null value
   in the third column.
<programlisting>
0000000   P   G   C   O   P   Y  \n 377  \r  \n  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0 003  \0  \0  \0 002   A   F  \0  \0  \0 013   A
0000040   F   G   H   A   N   I   S   T   A   N 377 377 377 377  \0 003
0000060  \0  \0  \0 002   A   L  \0  \0  \0 007   A   L   B   A   N   I
0000100   A 377 377 377 377  \0 003  \0  \0  \0 002   D   Z  \0  \0  \0
0000120 007   A   L   G   E   R   I   A 377 377 377 377  \0 003  \0  \0
0000140  \0 002   Z   M  \0  \0  \0 006   Z   A   M   B   I   A 377 377
0000160 377 377  \0 003  \0  \0  \0 002   Z   W  \0  \0  \0  \b   Z   I
0000200   M   B   A   B   W   E 377 377 377 377 377 377
</programlisting></para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   There is no <command>COPY</command> statement in the SQL standard.
  </para>

  <para>
   The following syntax was used before <productname>PostgreSQL</productname>
   version 9.0 and is still supported:

<synopsis>
COPY <replaceable class="parameter">table_name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
    FROM { '<replaceable class="parameter">filename</replaceable>' | STDIN }
    [ [ WITH ]
          [ BINARY ]
          [ DELIMITER [ AS ] '<replaceable class="parameter">delimiter_character</replaceable>' ]
          [ NULL [ AS ] '<replaceable class="parameter">null_string</replaceable>' ]
          [ CSV [ HEADER ]
                [ QUOTE [ AS ] '<replaceable class="parameter">quote_character</replaceable>' ]
                [ ESCAPE [ AS ] '<replaceable class="parameter">escape_character</replaceable>' ]
                [ FORCE NOT NULL <replaceable class="parameter">column_name</replaceable> [, ...] ] ] ]

COPY { <replaceable class="parameter">table_name</replaceable> [ ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ] | ( <replaceable class="parameter">query</replaceable> ) }
    TO { '<replaceable class="parameter">filename</replaceable>' | STDOUT }
    [ [ WITH ]
          [ BINARY ]
          [ DELIMITER [ AS ] '<replaceable class="parameter">delimiter_character</replaceable>' ]
          [ NULL [ AS ] '<replaceable class="parameter">null_string</replaceable>' ]
          [ CSV [ HEADER ]
                [ QUOTE [ AS ] '<replaceable class="parameter">quote_character</replaceable>' ]
                [ ESCAPE [ AS ] '<replaceable class="parameter">escape_character</replaceable>' ]
                [ FORCE QUOTE { <replaceable class="parameter">column_name</replaceable> [, ...] | * } ] ] ]
</synopsis>

   Note that in this syntax, <literal>BINARY</literal> and <literal>CSV</literal> are
   treated as independent keywords, not as arguments of a <literal>FORMAT</literal>
   option.
  </para>

  <para>
   The following syntax was used before <productname>PostgreSQL</productname>
   version 7.3 and is still supported:

<synopsis>
COPY [ BINARY ] <replaceable class="parameter">table_name</replaceable>
    FROM { '<replaceable class="parameter">filename</replaceable>' | STDIN }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter_character</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null_string</replaceable>' ]

COPY [ BINARY ] <replaceable class="parameter">table_name</replaceable>
    TO { '<replaceable class="parameter">filename</replaceable>' | STDOUT }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter_character</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null_string</replaceable>' ]
</synopsis></para>
 </refsect1>
</refentry>