COPY() SQL Commands 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 DELIM‐
ITERS 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 back‐
end. 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 for‐
mat rather than as text. It is somewhat faster than the normal copy
command, but a binary copy file is not portable across machine archi‐
tectures.
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 mul‐
tiple 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 per‐
missions 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 prob‐
lems 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 back‐
end, 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 stan‐
dard input, it will expect a backslash ("\") and a period (".") fol‐
lowed 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 spe‐
cial end-of-file pattern is found.
The backslash character has other special meanings. A literal backslash
character is represented as two consecutive backslashes ("\\"). A lit‐
eral 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 prop‐
erly.
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 new‐
line-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 back‐
wards-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 con‐
tents 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 delib‐
erate: 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 han‐
dling 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 eas‐
ily 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 verti‐
cal 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.
SQL - Language Statements 29 March 2001 COPY()
