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 applica
tion.
stdout Specifies that output goes to the client applica
tion.
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.
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 fron
tend 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 accessi
bility 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 char
acter. If multiple characters are specified in the delim
iter 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.
lead to problems in the event of a COPY FROM, but the tar
get 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 consid
erable 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 per
missions, 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 rel
ative 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 them
selves are strings generated by the output function asso
ciated 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
If COPY TO is sending its output to standard output
instead of a file, after the last row it will send a back
slash ("\") 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 cor
rectly (followed by the backend itself) if the input con
nection is closed before this special end-of-file pattern
is found.
The backslash character has other special meanings. A lit
eral 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 new
line character is represented as a backslash and a new
line. 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, fol
lowed 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 identifi
cation 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
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.
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 dis
tinguish 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 immedi
ately follows the field-count word. It is a normal field
except that it's not included in the field-count. In par
ticular 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 pro
vides 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.
Man(1) output converted with
man2html