COPY — copy data between a file and a table
COPYtablename
[ (column
[, ...] ) ] FROM { 'filename
' | STDIN } [ [ WITH ] [ BINARY ] [ OIDS ] [ DELIMITER [ AS ] 'delimiter
' ] [ NULL [ AS ] 'null string
' ] [ CSV [ HEADER ] [ QUOTE [ AS ] 'quote
' ] [ ESCAPE [ AS ] 'escape
' ] [ FORCE NOT NULLcolumn
[, ...] ] COPY {tablename
[ (column
[, ...] ) ] | (query
) } TO { 'filename
' | STDOUT } [ [ WITH ] [ BINARY ] [ HEADER ] [ OIDS ] [ DELIMITER [ AS ] 'delimiter
' ] [ NULL [ AS ] 'null string
' ] [ CSV [ HEADER ] [ QUOTE [ AS ] 'quote
' ] [ ESCAPE [ AS ] 'escape
' ] [ FORCE QUOTEcolumn
[, ...] ]
COPY
moves data between
PostgreSQL tables and standard file-system
files. COPY TO
copies the 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 TO
can also copy the results of a SELECT
query.
If a list of columns is specified, COPY
will
only copy the data in the specified columns to or from the file.
If there are any columns in the table that are not in the column list,
COPY FROM
will insert the default values for
those columns.
COPY
with a file name instructs the
PostgreSQL server to directly read from
or write to a file. The file must be accessible to the server and
the name must be specified from the viewpoint of the server. When
STDIN
or STDOUT
is
specified, data is transmitted via the connection between the
client and the server.
tablename
The name (optionally schema-qualified) of an existing table.
column
An optional list of columns to be copied. If no column list is specified, all columns of the table will be copied.
query
A SELECT or VALUES command whose results are to be copied. Note that parentheses are required around the query.
filename
The absolute path name of the input or output file. Windows users
might need to use an E''
string and double backslashes
used as path separators.
STDIN
Specifies that input comes from the client application.
STDOUT
Specifies that output goes to the client application.
BINARY
Causes all data to be stored or read in binary format rather
than as text. You cannot specify the DELIMITER
,
NULL
, or CSV
options in binary mode.
OIDS
Specifies copying the OID for each row. (An error is raised if
OIDS
is specified for a table that does not
have OIDs, or in the case of copying a query
.)
delimiter
The single character that separates columns within each row
(line) of the file. The default is a tab character in text mode,
a comma in CSV
mode.
null string
The string that represents a null value. The default is
\N
(backslash-N) in text mode, and a empty
value with no quotes in CSV
mode. You might prefer an
empty string even in text mode for cases where you don't want to
distinguish nulls from empty strings.
When using COPY FROM
, 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 with
COPY TO
.
CSV
Selects Comma Separated Value (CSV
) mode.
HEADER
Specifies the file contains a header line with the names of each column in the file. On output, the first line contains the column names from the table, and on input, the first line is ignored.
quote
Specifies the quotation character in CSV
mode.
The default is double-quote.
escape
Specifies the character that should appear before a
QUOTE
data character value in CSV
mode.
The default is the QUOTE
value (usually double-quote).
FORCE QUOTE
In CSV
COPY TO
mode, forces quoting to be
used for all non-NULL
values in each specified column.
NULL
output is never quoted.
FORCE NOT NULL
In CSV
COPY FROM
mode, process each
specified column as though it were quoted and hence not a
NULL
value. For the default null string in
CSV
mode (''
), this causes missing
values to be input as zero-length strings.
On successful completion, a COPY
command returns a command
tag of the form
COPY count
The count
is the number
of rows copied.
COPY
can only be used with plain tables, not
with views. However, you can write COPY (SELECT * FROM
.
viewname
) TO ...
The BINARY
key word causes all data to be
stored/read as binary format rather than as text. It is
somewhat faster than the normal text mode, but a binary-format
file is less portable across machine architectures and
PostgreSQL versions.
You must have select privilege on the table
whose values are read by COPY TO
, and
insert privilege on the table into which values
are inserted by COPY FROM
.
Files named in a COPY
command are read or written
directly by the server, 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 PostgreSQL user (the user ID the
server runs as), not the client. COPY
naming a
file is only allowed to database superusers, since it allows reading
or writing any file that the server has privileges to access.
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 server when \copy
is used.
It is recommended that the file name used in COPY
always be specified as an absolute path. This is enforced by the
server 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 working directory of the server process (normally
the cluster's data directory), not the client's working directory.
COPY FROM
will invoke any triggers and check
constraints on the destination table. However, it will not invoke rules.
COPY
input and output is affected by
DateStyle
. To ensure portability to other
PostgreSQL installations that might use
non-default DateStyle
settings,
DateStyle
should be set to ISO
before
using COPY TO
.
COPY
stops operation at the first error. This
should not lead to problems in the event of a COPY
TO
, but the target table will already have received
earlier rows in a COPY FROM
. 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.
When COPY
is used without the BINARY
or CSV
options,
the data read or written is a text file with one line per table row.
Columns in a row are separated by the delimiter character.
The column values themselves are strings generated by the
output function, or acceptable to the input function, of each
attribute's data type. The specified null string is used in
place of columns that are null.
COPY FROM
will raise an error if any line of the
input file contains more or fewer columns than are expected.
If OIDS
is specified, the OID is read or written as the first column,
preceding the user data columns.
End of data can be represented by a single line containing just
backslash-period (\.
). An end-of-data marker is
not necessary when reading from a file, since the end of file
serves perfectly well; it is needed only when copying data to or from
client applications using pre-3.0 client protocol.
Backslash characters (\
) may be used in the
COPY
data to quote data characters that might
otherwise be taken as row or column delimiters. In particular, the
following characters must be preceded by a backslash if
they appear as part of a column value: backslash itself,
newline, carriage return, and the current delimiter character.
The specified null string is sent by COPY TO
without
adding any backslashes; conversely, COPY FROM
matches
the input against the null string before removing backslashes. Therefore,
a null string such as \N
cannot be confused with
the actual data value \N
(which would be represented
as \\N
).
The following special backslash sequences are recognized by
COPY FROM
:
Sequence | Represents |
---|---|
\b |
Backspace (ASCII 8) |
\f |
Form feed (ASCII 12) |
\n |
Newline (ASCII 10) |
\r |
Carriage return (ASCII 13) |
\t |
Tab (ASCII 9) |
\v |
Vertical tab (ASCII 11) |
\ digits
|
Backslash followed by one to three octal digits specifies the character with that numeric code |
\x digits
|
Backslash x followed by one or two hex digits specifies
the character with that numeric code |
Presently, COPY TO
will never emit an octal or
hex-digits backslash sequence, but it does use the other sequences
listed above for those control characters.
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 (\.
) or the null string (\N
by
default). These strings will be recognized before any other backslash
processing is done.
It is strongly recommended that applications generating COPY
data convert
data newlines and carriage returns to the \n
and
\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 COPY
file is
transferred across different machines (for example, from Unix to Windows
or vice versa).
COPY TO
will terminate each row with a Unix-style
newline (“\n
”). Servers running on Microsoft Windows instead
output carriage return/newline (“\r\n
”), but only for
COPY
to a server file; for consistency across platforms,
COPY TO STDOUT
always sends “\n
”
regardless of server platform.
COPY FROM
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, COPY FROM
will complain if the line
endings in the input are not all alike.
This format is used for importing and exporting the Comma
Separated Value (CSV
) file format used by many other
programs, such as spreadsheets. Instead of the escaping used by
PostgreSQL's standard text mode, it
produces and recognizes the common CSV escaping mechanism.
The values in each record are separated by the DELIMITER
character. If the value contains the delimiter character, the
QUOTE
character, the NULL
string, a carriage
return, or line feed character, then the whole value is prefixed and
suffixed by the QUOTE
character, and any occurrence
within the value of a QUOTE
character or the
ESCAPE
character is preceded by the escape character.
You can also use FORCE QUOTE
to force quotes when outputting
non-NULL
values in specific columns.
The CSV
format has no standard way to distinguish a
NULL
value from an empty string.
PostgreSQL's COPY
handles this by
quoting. A NULL
is output as the NULL
string and is not quoted, while a data value matching the
NULL
string is quoted. Therefore, using the default
settings, a NULL
is written as an unquoted empty
string, while an empty string is written with double quotes
(""
). Reading values follows similar rules. You can
use FORCE NOT NULL
to prevent NULL
input
comparisons for specific columns.
Because backslash is not a special character in the CSV
format, \.
, the end-of-data marker, could also appear
as a data value. To avoid any misinterpretation, a \.
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 \.
, you might need to quote that value in the
input file.
In CSV
mode, all characters are significant. A quoted value
surrounded by white space, or any characters other than
DELIMITER
, will include those characters. This can cause
errors if you import data from a system that pads CSV
lines with white space out to some fixed width. If such a situation
arises you might need to preprocess the CSV
file to remove
the trailing white space, before importing the data into
PostgreSQL.
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.
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 COPY
might produce files that other
programs cannot process.
The file format used for COPY BINARY
changed in
PostgreSQL 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.
The file header consists of 15 bytes of fixed fields, followed by a variable-length header extension area. The fixed fields are:
11-byte sequence PGCOPY\n\377\r\n\0
— 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.)
32-bit integer 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 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:
if 1, OIDs are included in the data; if 0, not
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.
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).
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.
There is no alignment padding or any other extra data between fields.
Presently, all data values in a COPY BINARY
file are
assumed to be in binary format (format code one). It is anticipated that a
future extension may add a header field that allows per-column format codes
to be specified.
To determine the appropriate binary format for the actual tuple data you
should consult the PostgreSQL source, in
particular the *send
and *recv
functions for
each column's data type (typically these functions are found in the
src/backend/utils/adt/
directory of the source
distribution).
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 — 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.
The file trailer consists of a 16-bit integer 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.
The following example copies a table to the client
using the vertical bar (|
) as the field delimiter:
COPY country TO STDOUT WITH DELIMITER '|';
To copy data from a file into the country
table:
COPY country FROM '/usr1/proj/bray/sql/country_data';
To copy into a file just the countries whose names start with 'A':
COPY (SELECT * FROM country WHERE country_name LIKE 'A%') TO '/usr1/proj/bray/sql/a_list_countries.copy';
Here is a sample of data suitable for copying into a table from
STDIN
:
AF AFGHANISTAN AL ALBANIA DZ ALGERIA ZM ZAMBIA ZW ZIMBABWE
Note that the white space on each line is actually a tab character.
The following is the same data, output in binary format.
The data is shown after filtering through the
Unix utility od -c
. The table has three columns;
the first has type char(2)
, the second has type text
,
and the third has type integer
. All the rows have a null value
in the third column.
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
There is no COPY
statement in the SQL standard.
The following syntax was used before PostgreSQL version 7.3 and is still supported:
COPY [ BINARY ]tablename
[ WITH OIDS ] FROM { 'filename
' | STDIN } [ [USING] DELIMITERS 'delimiter
' ] [ WITH NULL AS 'null string
' ] COPY [ BINARY ]tablename
[ WITH OIDS ] TO { 'filename
' | STDOUT } [ [USING] DELIMITERS 'delimiter
' ] [ WITH NULL AS 'null string
' ]