copy.sgml

postgresql8.3.4源码,开源数据库

    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</></entry>
       <entry>Backspace (ASCII 8)</entry>
      </row>
      <row>
       <entry><literal>\f</></entry>
       <entry>Form feed (ASCII 12)</entry>
      </row>
      <row>
       <entry><literal>\n</></entry>
       <entry>Newline (ASCII 10)</entry>
      </row>
      <row>
       <entry><literal>\r</></entry>
       <entry>Carriage return (ASCII 13)</entry>
      </row>
      <row>
       <entry><literal>\t</></entry>
       <entry>Tab (ASCII 9)</entry>
      </row>
      <row>
       <entry><literal>\v</></entry>
       <entry>Vertical tab (ASCII 11)</entry>
      </row>
      <row>
       <entry><literal>\</><replaceable>digits</></entry>
       <entry>Backslash followed by one to three octal digits specifies
       the character with that numeric code</entry>
      </row>
      <row>
       <entry><literal>\x</><replaceable>digits</></entry>
       <entry>Backslash <literal>x</> 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>\.</>) or the null string (<literal>\N</> 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</> and
    <literal>\r</> 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</></>).  Servers running on Microsoft Windows instead
    output carriage return/newline (<quote><literal>\r\n</></>), but only for
    <command>COPY</> to a server file; for consistency across platforms,
    <command>COPY TO STDOUT</> always sends <quote><literal>\n</></>
    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 is used for importing and exporting the Comma
    Separated Value (<literal>CSV</>) file format used by many other
    programs, such as spreadsheets. Instead of the escaping used by
    <productname>PostgreSQL</productname>'s standard text mode, it
    produces and recognizes the common CSV escaping mechanism.
   </para>

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

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

   <para> 
    Because backslash is not a special character in the <literal>CSV</>
    format, <literal>\.</>, the end-of-data marker, could also appear
    as a data value.  To avoid any misinterpretation, a <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>\.</>, you might need to quote that value in the 
    input file.
   </para>

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

   <note>
    <para>
     CSV mode 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-mode
     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</> might produce files that other
     programs cannot process.
    </para>
   </note>
    
  </refsect2>

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

   <para>
    The file format used for <command>COPY BINARY</command> changed in
    <productname>PostgreSQL</productname> 7.4. The new format consists
    of a file header, zero or more tuples containing the row data, and
    a file trailer. Headers and data are now in network byte order.
   </para>

   <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</> &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</>) to 31 (<acronym>MSB</>).  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
           </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 <command>COPY BINARY</command> 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</> and <function>*recv</> 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.  In particular it has a length word &mdash; 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 that ever proves desirable.
    </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 WITH DELIMITER '|';
</programlisting>
  </para>

  <para>
   To copy data from a file into the <literal>country</> 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>
   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</>
   version 7.3 and is still supported:

<synopsis>
COPY [ BINARY ] <replaceable class="parameter">tablename</replaceable> [ WITH OIDS ]
    FROM { '<replaceable class="parameter">filename</replaceable>' | STDIN }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null string</replaceable>' ]

COPY [ BINARY ] <replaceable class="parameter">tablename</replaceable> [ WITH OIDS ]
    TO { '<replaceable class="parameter">filename</replaceable>' | STDOUT }
    [ [USING] DELIMITERS '<replaceable class="parameter">delimiter</replaceable>' ]
    [ WITH NULL AS '<replaceable class="parameter">null string</replaceable>' ]
</synopsis>
  </para>
 </refsect1>
</refentry>