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COPY

Name

COPY  --  Copies data between files and tables

Synopsis

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. The DELIMITERS and WITH NULL options are irrelevant for binary format.

table

The name of an existing table.

WITH OIDS

Specifies copying 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 the client application.

stdout

Specifies that output goes to the client application.

delimiter

The character that separates fields within each row (line) of the file.

null string

The string that represents a NULL value. 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 TO copies the entire contents of a table to a file, while COPY FROM copies data from a file to a table (appending the data to whatever is in the table already).

COPY instructs the Postgres 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 stdin or stdout is specified, data flows through the client frontend to the backend.

Tip: Do not confuse COPY with the psql instruction \copy. \copy invokes COPY FROM stdin or COPY TO stdout, and then fetches/stores the data in a file accessible to the psql client. Thus, file accessibility and access rights depend on the client rather than the backend when \copy is used.

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 a binary copy file is not portable across machine architectures.

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.

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.

COPY TO neither invokes rules nor acts on column defaults. It does invoke triggers and check constraints.

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 already have received earlier rows in a COPY TO. 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 VACUUM to recover the wasted space.

Files named in a COPY 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. COPY 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: The psql instruction \copy reads or writes files on the client machine with the client's permissions, so it is not restricted to superusers.

It is recommended that the filename used in COPY always be specified as an absolute path. This is enforced by the backend in the case of COPY TO, but for COPY FROM 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 $PGDATA), not the client's working directory.

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>
    
Note that the end of each row is marked by a Unix-style newline ("\n"). COPY FROM will not behave as desired if given a file containing DOS- or Mac-style newlines.

The OID is emitted as the first column if WITH OIDS is specified.

If COPY TO 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 COPY FROM 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 FROM will terminate correctly (followed by the backend itself) if the input connection is closed 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. (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 Postgres, you will need to convert backslash characters ("\") to double-backslashes ("\\") to ensure that they are loaded properly.

Binary Format

The file format used for COPY BINARY changed in Postgres v7.1. The new format consists of a file header, zero or more tuples, and a file trailer.

File Header

The file header consists of 24 bytes of fixed fields, followed by a variable-length header extension area. The fixed fields are:

Signature

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.)

Integer layout field

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.

Flags field

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:

Bit 16

if 1, OIDs are included in the dump; if 0, not

Header extension area length

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.

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.

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).

Tuples

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:

Zero

Field is NULL. No data follows.

> 0

Field is a fixed-length datatype. Exactly N bytes of data follow the typlen word.

-1

Field is a varlena datatype. The next four bytes are the varlena header, which contains the total value length including itself.

< -1

Reserved for future use.

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.

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).

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.

File Trailer

The file trailer consists of an int16 word containing -1. This is easily distinguished from a tuple's field-count word.

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.

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
\.
  

Note that the white space on each line is actually a TAB.

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 od -c. The table has three fields; the first is char(2), the second is text, and the third is integer. All the rows have a null value in the third field.

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
  

Compatibility

SQL92

There is no COPY statement in SQL92.

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