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COPY

Name

COPY — Copies data between files and tables
COPY [ BINARY ] table [ WITH OIDS ]
    FROM { 'filename' | stdin }
    [ [USING] DELIMITERS 'delimiter' ]
    [ WITH NULL AS 'null string' ]
COPY [ BINARY ] table [ WITH OIDS ]
    TO { 'filename' | stdout }
    [ [USING] DELIMITERS 'delimiter' ]
    [ WITH NULL AS 'null string' ]
  

Inputs

BINARY

Changes the behavior of field formatting, forcing all data to be stored or read in binary format rather than as text.

table

The name of an existing table.

WITH OIDS

Copies the internal unique object id (OID) for each row.

filename

The absolute Unix pathname of the input or output file.

stdin

Specifies that input comes from a pipe or terminal.

stdout

Specifies that output goes to a pipe or terminal.

delimiter

A character that delimits the input or output fields.

null print

A string to represent NULL values. The default is “\N” (backslash-N). You might prefer an empty string, for example.

Note: 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.

Outputs

COPY

The copy completed successfully.

ERROR: reason

The copy failed for the reason stated in the error message.

Description

COPY moves data between Postgres tables and standard file-system files. COPY instructs the Postgres backend to directly read from or write to a file. The file must be directly visible to the backend and the name must be specified from the viewpoint of the backend. If stdin or stdout are specified, data flows through the client frontend to the backend.

Notes

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 is not generally portable, and the files generated are somewhat larger, although this factor is highly dependent on the data itself.

By default, a text copy uses a tab ("\t") character as a delimiter. The delimiter may also 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.

You must have select access on any table whose values are read by COPY, and either insert or update access to a table into which values are being inserted by COPY. The backend also needs appropriate Unix permissions for any file read or written by COPY.

The keyword phrase USING DELIMITERS specifies a single character to be used for all delimiters between columns. If multiple characters are specified in the delimiter string, only the first character is used.

Tip: Do not confuse COPY with the psql instruction \copy.

COPY neither invokes rules nor acts on column defaults. It does invoke triggers, however.

COPY stops operation at the first error. This should not lead to problems in the event of a COPY FROM, but the target relation will, of course, be partially modified in a COPY TO. VACUUM should be used to clean up after a failed copy.

Because the Postgres backend's current working directory is not usually the same as the user's working directory, the result of copying to a file "foo" (without additional path information) may yield unexpected results for the naive user. In this case, foo will wind up in $PGDATA/foo. In general, the full pathname as it would appear to the backend server machine should be used when specifying files to be copied.

Files used as arguments to COPY must reside on or be accessible to the database server machine by being either on local disks or on a networked file system.

When a TCP/IP connection from one machine to another is used, and a target file is specified, the target file will be written on the machine where the backend is running rather than the user's machine.

File Formats

Text Format

When COPY TO 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 COPY itself.

The actual format for each instance is

<attr1><separator><attr2><separator>...<separator><attrn><newline>
    
The oid is placed on the beginning of the line if WITH OIDS is specified.

If COPY is sending its output to standard output instead of a file, it will send a backslash("\") and a period (".") followed immediately by a newline, on a separate line, when it is done. Similarly, if COPY 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, COPY will terminate (followed by the backend itself) if a true EOF is encountered before this special end-of-file pattern is found.

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. A literal newline character is represented as a backslash and a newline. When loading text data not generated by Postgres, you will need to convert backslash characters ("\") to double-backslashes ("\\") to ensure that they are loaded properly.

Binary Format

In the case of COPY BINARY, the first four bytes in the file will be the number of instances in the file. If this number is zero, the COPY BINARY command will read until end of file is encountered. Otherwise, it will stop reading when this number of instances has been read. Remaining data in the file will be ignored.

The format for each instance in the file is as follows. Note that this format must be followed exactly. Unsigned four-byte integer quantities are called uint32 in the table below.

Table 19-1. Contents of a binary copy file

At the start of the file
uint32 number of tuples
For each tuple
uint32 total length of tuple data
uint32 oid (if specified)
uint32 number of null attributes
[uint32,...,uint32] attribute numbers of attributes, counting from 0
- <tuple data>

Alignment of Binary Data

On Sun-3s, 2-byte attributes are aligned on two-byte boundaries, and all larger attributes are aligned on four-byte boundaries. Character attributes are aligned on single-byte boundaries. On most other machines, all attributes larger than 1 byte are aligned on four-byte boundaries. Note that variable length attributes are preceded by the attribute's length; arrays are simply contiguous streams of the array element type.

Usage

The following example copies a table to standard output, using a vertical bar ("|") as the field delimiter:

COPY country TO stdout USING DELIMITERS '|';
  

To copy data from a Unix file into a table "country":

COPY country FROM '/usr1/proj/bray/sql/country_data';
  

Here is a sample of data suitable for copying into a table from stdin (so it has the termination sequence on the last line):

   AF      AFGHANISTAN
   AL      ALBANIA
   DZ      ALGERIA
   ...
   ZM      ZAMBIA
   ZW      ZIMBABWE
   \.
  

The same data, output in binary format on a Linux/i586 machine. The data is shown after filtering through the Unix utility od -c. The table has three fields; the first is char(2) and the second is text. All the rows have a null value in the third field. Notice how the char(2) field is padded with nulls to four bytes and the text field is preceded by its length:

   355  \0  \0  \0 027  \0  \0  \0 001  \0  \0  \0 002  \0  \0  \0
   006  \0  \0  \0   A   F  \0  \0 017  \0  \0  \0   A   F   G   H
     A   N   I   S   T   A   N 023  \0  \0  \0 001  \0  \0  \0 002
    \0  \0  \0 006  \0  \0  \0   A   L  \0  \0  \v  \0  \0  \0   A
     L   B   A   N   I   A 023  \0  \0  \0 001  \0  \0  \0 002  \0
    \0  \0 006  \0  \0  \0   D   Z  \0  \0  \v  \0  \0  \0   A   L
     G   E   R   I   A
   ...              \n  \0  \0  \0   Z   A   M   B   I   A 024  \0
    \0  \0 001  \0  \0  \0 002  \0  \0  \0 006  \0  \0  \0   Z   W
    \0  \0  \f  \0  \0  \0   Z   I   M   B   A   B   W   E
  

Compatibility

SQL92

There is no COPY statement in SQL92.

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