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$Header: /cvsroot/pgsql/doc/src/sgml/ref/copy.sgml,v 1.20 2001/01/13 23:58:55 petere Exp $
Postgres documentation
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<refentry id="SQL-COPY">
 <refmeta>
  <refentrytitle id="sql-copy-title">
   COPY
  </refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   COPY
  </refname>
  <refpurpose>
   Copies data between files and tables
  </refpurpose>
 </refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>1999-12-11</date>
  </refsynopsisdivinfo>
  <synopsis>
COPY [ BINARY ] <replaceable class="parameter">table</replaceable> [ WITH OIDS ]
    FROM { '<replaceable class="parameter">filename</replaceable>' | <filename>stdin</filename> }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null string</replaceable>' ]
COPY [ BINARY ] <replaceable class="parameter">table</replaceable> [ WITH OIDS ]
    TO { '<replaceable class="parameter">filename</replaceable>' | <filename>stdout</filename> }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null string</replaceable>' ]
  </synopsis>
  
  <refsect2 id="R2-SQL-COPY-1">
   <refsect2info>
    <date>1998-09-08</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term>BINARY</term>
      <listitem>
       <para>
	Changes the behavior of field formatting, forcing all data to be
	stored or read in binary format rather than as text.
	The DELIMITERS and WITH NULL options are irrelevant for binary format.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">table</replaceable></term>
      <listitem>
       <para>
	The name of an existing table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>WITH OIDS</term>
      <listitem>
       <para>
	Specifies copying the internal unique object id (OID) for each row.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">filename</replaceable></term>
      <listitem>
       <para>
	The absolute Unix pathname of the input or output file.
       </para>
      </listitem>
     </varlistentry>

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

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

     <varlistentry>
      <term><replaceable class="parameter">delimiter</replaceable></term>
      <listitem>
       <para>
	The character that separates fields within each row (line) of the file.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">null string</replaceable></term>
      <listitem>
       <para>
        The string that represents a NULL value. The default is
        <quote><literal>\N</literal></quote> (backslash-N).
	You might prefer an empty string, for example.
       </para>
       <note>
        <para>
         On a copy in, 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 on copy out.
        </para>
       </note>
      </listitem>
     </varlistentry>

    </variablelist>
   </para>
  </refsect2>
  
  <refsect2 id="R2-SQL-COPY-2">
   <refsect2info>
    <date>1998-09-08</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <para>

    <variablelist>
     <varlistentry>
      <term><computeroutput>
COPY
       </computeroutput></term>
      <listitem>
       <para>
	The copy completed successfully.
       </para>
      </listitem>
     </varlistentry>
     <varlistentry>
      <term><computeroutput>
ERROR: <replaceable>reason</replaceable>
       </computeroutput></term>
      <listitem>
       <para>
	The copy failed for the reason stated in the error message.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
  </refsect2>
 </refsynopsisdiv>
 
 <refsect1 id="R1-SQL-COPY-1">
  <refsect1info>
   <date>2001-01-02</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   <command>COPY</command> moves data between
   <productname>Postgres</productname> tables and
   standard file-system files.

   <command>COPY TO</command> copies the entire contents of a table to
   a file, while <command>COPY FROM</command> copies data from a file to a
   table (appending the data to whatever is in the table already).
  </para>

  <para>
   <command>COPY</command> instructs
   the <productname>Postgres</productname> backend
   to directly read from or write to a file. If a file name is specified,
   the file must be accessible to the backend and the name must be specified
   from the viewpoint of the backend.
   If <filename>stdin</filename> or <filename>stdout</filename> is
   specified, data flows through the client frontend to  the backend.
    
    <tip>
     <para>
      Do not confuse <command>COPY</command> with the
      <application>psql</application> instruction <command>\copy</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 backend when <command>\copy</command> is used.
     </para>
    </tip>
   </para>

  <refsect2 id="R2-SQL-COPY-3">
   <refsect2info>
    <date>2001-01-02</date>
   </refsect2info>
   <title>
    Notes
   </title>
   <para>
    The BINARY keyword will force all data to be
    stored/read as binary format rather than as text.  It is
    somewhat faster than the normal copy command, but a binary copy
    file is not portable across machine architectures.
    </para>

    <para>
    By default, a text copy uses a tab ("\t") character as a delimiter
    between fields.  The field delimiter may be changed to any other single
    character with the keyword phrase USING DELIMITERS.  Characters
    in data fields which happen to match the delimiter character will
    be backslash quoted.
    Note that the delimiter is always a single character.
    If multiple characters are specified in the delimiter string,
    only the first character is used.
   </para>
   
   <para>
    You must have <firstterm>select access</firstterm> on any table
    whose values are read by
    <command>COPY</command>, and either
    <firstterm>insert</firstterm> or <firstterm>update access</firstterm> to a
    table into which values are being inserted by <command>COPY</command>.
    The backend also needs appropriate Unix permissions for any file read
    or written by <command>COPY</command>.
   </para>

   <para>
    <command>COPY TO</command> neither invokes rules nor acts on column
    defaults.  It does invoke triggers and check constraints.
   </para>

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

   <para>
    Files named in a <command>COPY</command> command are read or written
    directly by the backend, 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 Postgres user (the userid the backend runs as), not the client.
    <command>COPY</command> naming a file is only allowed to database
    superusers, since it allows writing on any file that the backend has
    privileges to write on.
    
    <tip>
     <para>
      The
      <application>psql</application> instruction <command>\copy</command>
      reads or writes files on the client machine with the client's
      permissions, so it is not restricted to superusers.
     </para>
    </tip>
   </para>

   <para>
    It is recommended that the filename used in <command>COPY</command>
    always be specified as an absolute path.  This is enforced by the backend
    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
    backend's working directory (somewhere below
    <filename>$PGDATA</filename>), not the client's working directory.
   </para>
  </refsect2>
 </refsect1>
 
 <refsect1 id="R1-SQL-COPY-2">
  <refsect1info>
   <date>2001-01-02</date>
  </refsect1info>
  <title>File Formats</title>
  <refsect2>
   <refsect2info>
    <date>2001-01-02</date>
   </refsect2info>
   <title>Text Format</title>
   <para>
    When <command>COPY TO</command> is used without the BINARY option,
    the file generated will have each row (instance) on a single line, with each
    column (attribute) separated by the delimiter character.  Embedded
    delimiter characters will be preceded by a backslash character
    ("\").  The attribute values themselves are strings generated by the
    output function associated with each attribute type.  The output
    function for a type should not try to generate the backslash
    character; this will be handled by <command>COPY</command> itself.
   </para>
   <para>
    The actual format for each instance is
    <programlisting>
&lt;attr1&gt;&lt;<replaceable class=parameter>separator</replaceable>&gt;&lt;attr2&gt;&lt;<replaceable class=parameter>separator</replaceable>&gt;...&lt;<replaceable class=parameter>separator</replaceable>&gt;&lt;attr<replaceable class="parameter">n</replaceable>&gt;&lt;newline&gt;
    </programlisting>
    Note that the end of each row is marked by a Unix-style newline
    ("\n").  <command>COPY FROM</command> will not behave as desired
    if given a file containing DOS- or Mac-style newlines.
   </para>
   <para>
    The OID is emitted as the first column if WITH OIDS is specified.
   </para>
   <para>
    If <command>COPY TO</command> is sending its output to standard
    output instead of a file, after the last row it will send a backslash ("\")
    and a period (".") followed by a newline.
    Similarly, if <command>COPY FROM</command> is reading
    from standard input, it will expect a backslash ("\") and a period
    (".") followed by a newline, as the first three characters on a
    line to denote end-of-file.  However, <command>COPY FROM</command>
    will terminate correctly (followed by the backend itself) if the
    input connection is closed before this special end-of-file pattern is
    found.
   </para>
   <para>
    The backslash character has other special meanings.  A literal backslash
    character is represented as two
    consecutive backslashes ("\\").  A literal tab character is represented
    as a backslash and a tab.  (If you are using something other than tab
    as the column delimiter, backslash that delimiter character to include
    it in data.)  A literal newline character is
    represented as a backslash and a newline.  When loading text data
    not generated by <acronym>Postgres</acronym>,
    you will need to convert backslash
    characters ("\") to double-backslashes ("\\") to ensure that they 
    are loaded properly.
   </para>
  </refsect2>

  <refsect2>
   <refsect2info>
    <date>2001-01-02</date>
   </refsect2info>
   <title>Binary Format</title>
   <para>
    The file format used for <command>COPY BINARY</command> changed in
    Postgres v7.1.  The new format consists of a file header, zero or more
    tuples, and a file trailer.
   </para>

   <refsect3>
    <refsect3info>
     <date>2001-01-02</date>
    </refsect3info>
    <title>
     File Header
    </title>
    <para>
     The file header consists of 24 bytes of fixed fields, followed
     by a variable-length header extension area.  The fixed fields are:

    <variablelist>
     <varlistentry>
      <term>Signature</term>
      <listitem>
       <para>
12-byte sequence "PGBCOPY\n\377\r\n\0" --- note that the null
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 newline-translation
filters, dropped nulls, dropped high bits, or parity changes.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Integer layout field</term>
      <listitem>
       <para>
int32 constant 0x01020304 in source's byte order.
Potentially, a reader could engage in byte-flipping of subsequent fields
if the wrong byte order is detected here.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Flags field</term>
      <listitem>
       <para>
int32 bit mask to denote important aspects of the file
format.  Bits are numbered from 0 (LSB) to 31 (MSB) --- note that this
field is stored with source's endianness, as are all subsequent integer
fields.  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 dump; if 0, not
           </para>
          </listitem>
         </varlistentry>
        </variablelist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>Header extension area length</term>
      <listitem>
       <para>
int32 length in bytes of remainder of header, not including self.  In
the initial version this will be 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>
    <refsect3info>
     <date>2001-01-02</date>
    </refsect3info>
    <title>
     Tuples
    </title>
    <para>
Each tuple begins with an int16 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 an int16 typlen word possibly followed by field data.
The typlen field is interpreted thus:

    <variablelist>
     <varlistentry>
      <term>Zero</term>
      <listitem>
       <para>
	Field is NULL.  No data follows.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>&gt; 0</term>
      <listitem>
       <para>
        Field is a fixed-length datatype.  Exactly N
	bytes of data follow the typlen word.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>-1</term>
      <listitem>
       <para>
	Field is a varlena datatype.  The next four
	bytes are the varlena header, which contains
	the total value length including itself.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>&lt; -1</term>
      <listitem>
       <para>
	Reserved for future use.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
    </para>

    <para>
For non-NULL fields, the reader can check that the typlen matches the
expected typlen for the destination column.  This provides a simple
but very useful check that the data is as expected.
    </para>

    <para>
There is no alignment padding or any other extra data between fields.
Note also that the format does not distinguish whether a datatype is
pass-by-reference or pass-by-value.  Both of these provisions are
deliberate: they might help improve portability of the files (although
of course endianness and floating-point-format issues can still keep
you from moving a binary file across machines).
    </para>

    <para>
If OIDs are included in the dump, the OID field immediately follows the
field-count word.  It is a normal field except that it's not included
in the field-count.  In particular it has a typlen --- this will allow
handling of 4-byte vs 8-byte OIDs without too much pain, and will allow
OIDs to be shown as NULL if we someday allow OIDs to be optional.
    </para>
   </refsect3>

   <refsect3>
    <refsect3info>
     <date>2001-01-02</date>
    </refsect3info>
    <title>
     File Trailer
    </title>
    <para>
     The file trailer consists of an int16 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 id="R1-SQL-COPY-3">
  <title>
   Usage
  </title>
  <para>
The following example copies a table to standard output,
 using a vertical bar (|) as the field
 delimiter:
  </para>
  <programlisting>
COPY country TO <filename>stdout</filename> USING DELIMITERS '|';
  </programlisting>
  <para>
   To copy data from a Unix file into a table country:
  </para>
  <programlisting>
COPY country FROM '/usr1/proj/bray/sql/country_data';
  </programlisting>
  <para>
   Here is a sample of data suitable for copying into a table
 from <filename>stdin</filename> (so it
has the termination sequence on the last line):
  </para>
  <programlisting>
AF      AFGHANISTAN
AL      ALBANIA
DZ      ALGERIA
ZM      ZAMBIA
ZW      ZIMBABWE
\.
  </programlisting>
  <para>
   Note that the white space on each line is actually a TAB.
  </para>
  <para>
   The following is the same data, output in binary format on a Linux/i586
   machine. The data is shown after filtering through
   the Unix utility <command>od -c</command>. The table has
   three fields; the first is <type>char(2)</type>,
   the second is <type>text</type>, and the third is
   <type>integer</type>. All the
   rows have a null value in the third field.
  </para>
  <programlisting>
0000000   P   G   B   C   O   P   Y  \n 377  \r  \n  \0 004 003 002 001
0000020  \0  \0  \0  \0  \0  \0  \0  \0 003  \0 377 377 006  \0  \0  \0
0000040   A   F 377 377 017  \0  \0  \0   A   F   G   H   A   N   I   S
0000060   T   A   N  \0  \0 003  \0 377 377 006  \0  \0  \0   A   L 377
0000100 377  \v  \0  \0  \0   A   L   B   A   N   I   A  \0  \0 003  \0
0000120 377 377 006  \0  \0  \0   D   Z 377 377  \v  \0  \0  \0   A   L
0000140   G   E   R   I   A  \0  \0 003  \0 377 377 006  \0  \0  \0   Z
0000160   M 377 377  \n  \0  \0  \0   Z   A   M   B   I   A  \0  \0 003
0000200  \0 377 377 006  \0  \0  \0   Z   W 377 377  \f  \0  \0  \0   Z
0000220   I   M   B   A   B   W   E  \0  \0 377 377
  </programlisting>
 </refsect1>
 
 <refsect1 id="R1-SQL-COPY-6">
  <title>
   Compatibility
  </title>
  
  <refsect2 id="R2-SQL-COPY-4">
   <refsect2info>
    <date>1998-09-08</date>
   </refsect2info>
   <title>
    SQL92
   </title>
   <para>
    There is no <command>COPY</command> statement in SQL92.
   </para>
  </refsect2>
 </refsect1>
</refentry>

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