COPY — copy data between a file and a table
COPYtable_name
[ (column_name
[, ...] ) ] FROM { 'filename
' | PROGRAM 'command
' | STDIN } [ [ WITH ] (option
[, ...] ) ] [ WHEREcondition
] COPY {table_name
[ (column_name
[, ...] ) ] | (query
) } TO { 'filename
' | PROGRAM 'command
' | STDOUT } [ [ WITH ] (option
[, ...] ) ] whereoption
can be one of: FORMATformat_name
FREEZE [boolean
] DELIMITER 'delimiter_character
' NULL 'null_string
' HEADER [boolean
] QUOTE 'quote_character
' ESCAPE 'escape_character
' FORCE_QUOTE { (column_name
[, ...] ) | * } FORCE_NOT_NULL (column_name
[, ...] ) FORCE_NULL (column_name
[, ...] ) ENCODING 'encoding_name
'
COPY
moves data between
LightDB 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 column list is specified, COPY TO
copies only
the data in the specified columns to the file. For COPY
FROM
, each field in the file is inserted, in order, into the
specified column. Table columns not specified in the COPY
FROM
column list will receive their default values.
COPY
with a file name instructs the
LightDB server to directly read from
or write to a file. The file must be accessible by the
LightDB user (the user ID the server
runs as) and the name must be specified from the viewpoint of the
server. When PROGRAM
is specified, the server
executes the given command and reads from the standard output of the
program, or writes to the standard input of the program. The command
must be specified from the viewpoint of the server, and be executable
by the LightDB user. When
STDIN
or STDOUT
is
specified, data is transmitted via the connection between the
client and the server.
table_name
The name (optionally schema-qualified) of an existing table.
column_name
An optional list of columns to be copied. If no column list is specified, all columns of the table except generated columns will be copied.
query
A SELECT, VALUES, INSERT, UPDATE or DELETE command whose results are to be copied. Note that parentheses are required around the query.
For INSERT
, UPDATE
and
DELETE
queries a RETURNING clause must be provided,
and the target relation must not have a conditional rule, nor
an ALSO
rule, nor an INSTEAD
rule
that expands to multiple statements.
filename
The path name of the input or output file. An input file name can be
an absolute or relative path, but an output file name must be an absolute
path. Windows users might need to use an E''
string and
double any backslashes used in the path name.
PROGRAM
A command to execute. In COPY FROM
, the input is
read from standard output of the command, and in COPY TO
,
the output is written to the standard input of the command.
Note that the command is invoked by the shell, so if you need to pass any arguments to shell command that come from an untrusted source, you must be careful to strip or escape any special characters that might have a special meaning for the shell. For security reasons, it is best to use a fixed command string, or at least avoid passing any user input in it.
STDIN
Specifies that input comes from the client application.
STDOUT
Specifies that output goes to the client application.
boolean
Specifies whether the selected option should be turned on or off.
You can write TRUE
, ON
, or
1
to enable the option, and FALSE
,
OFF
, or 0
to disable it. The
boolean
value can also
be omitted, in which case TRUE
is assumed.
FORMAT
Selects the data format to be read or written:
text
,
csv
(Comma Separated Values),
or binary
.
The default is text
.
FREEZE
Requests copying the data with rows already frozen, just as they
would be after running the VACUUM FREEZE
command.
This is intended as a performance option for initial data loading.
Rows will be frozen only if the table being loaded has been created
or truncated in the current subtransaction, there are no cursors
open and there are no older snapshots held by this transaction. It is
currently not possible to perform a COPY FREEZE
on
a partitioned table.
Note that all other sessions will immediately be able to see the data once it has been successfully loaded. This violates the normal rules of MVCC visibility and users specifying should be aware of the potential problems this might cause.
DELIMITER
Specifies the character that separates columns within each row
(line) of the file. The default is a tab character in text format,
a combination of up to 3 single one-byte characters is supported(Text),
a comma in CSV
format.
This must be a single one-byte character(CSV).
This option is not allowed when using binary
format.
NULL
Specifies the string that represents a null value. The default is
\N
(backslash-N) in text format, and an unquoted empty
string in CSV
format. You might prefer an
empty string even in text format for cases where you don't want to
distinguish nulls from empty strings.
This option is not allowed when using binary
format.
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
.
HEADER
Specifies that 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.
This option is allowed only when using CSV
format.
QUOTE
Specifies the quoting character to be used when a data value is quoted.
The default is double-quote.
This must be a single one-byte character.
This option is allowed only when using CSV
format.
ESCAPE
Specifies the character that should appear before a
data character that matches the QUOTE
value.
The default is the same as the QUOTE
value (so that
the quoting character is doubled if it appears in the data).
This must be a single one-byte character.
This option is allowed only when using CSV
format.
FORCE_QUOTE
Forces quoting to be
used for all non-NULL
values in each specified column.
NULL
output is never quoted. If *
is specified,
non-NULL
values will be quoted in all columns.
This option is allowed only in COPY TO
, and only when
using CSV
format.
FORCE_NOT_NULL
Do not match the specified columns' values against the null string.
In the default case where the null string is empty, this means that
empty values will be read as zero-length strings rather than nulls,
even when they are not quoted.
This option is allowed only in COPY FROM
, and only when
using CSV
format.
FORCE_NULL
Match the specified columns' values against the null string, even
if it has been quoted, and if a match is found set the value to
NULL
. In the default case where the null string is empty,
this converts a quoted empty string into NULL.
This option is allowed only in COPY FROM
, and only when
using CSV
format.
ENCODING
Specifies that the file is encoded in the encoding_name
. If this option is
omitted, the current client encoding is used. See the Notes below
for more details.
WHERE
The optional WHERE
clause has the general form
WHERE condition
where condition
is
any expression that evaluates to a result of type
boolean
. Any row that does not satisfy this
condition will not be inserted to the table. A row satisfies the
condition if it returns true when the actual row values are
substituted for any variable references.
Currently, subqueries are not allowed in WHERE
expressions, and the evaluation does not see any changes made by the
COPY
itself (this matters when the expression
contains calls to VOLATILE
functions).
On successful completion, a COPY
command returns a command
tag of the form
COPY count
The count
is the number
of rows copied.
ltsql will print this command tag only if the command
was not COPY ... TO STDOUT
, or the
equivalent ltsql meta-command
\copy ... to stdout
. This is to prevent confusing the
command tag with the data that was just printed.
COPY TO
can be used only with plain
tables, not views, and does not copy rows from child tables
or child partitions. For example, COPY
copies
the same rows as table
TOSELECT * FROM ONLY
.
The syntax table
COPY (SELECT * FROM
can be used to
dump all of the rows in an inheritance hierarchy, partitioned table,
or view.
table
) TO ...
COPY FROM
can be used with plain, foreign, or
partitioned tables or with views that have
INSTEAD OF INSERT
triggers.
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
. It is sufficient
to have column privileges on the column(s) listed in the command.
If row-level security is enabled for the table, the relevant
SELECT
policies will apply to COPY
statements.
Currently, table
TOCOPY FROM
is not supported for tables
with row-level security. Use equivalent INSERT
statements instead.
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 LightDB user (the user ID the
server runs as), not the client. Similarly,
the command specified with PROGRAM
is executed directly
by the server, not by the client application, must be executable by the
LightDB user.
COPY
naming a file or command is only allowed to
database superusers or users who are granted one of the default roles
pg_read_server_files
,
pg_write_server_files
,
or pg_execute_server_program
, since it allows reading
or writing any file or running a program that the server has privileges to
access.
Do not confuse COPY
with the
ltsql instruction
\copy
. \copy
invokes
COPY FROM STDIN
or COPY TO
STDOUT
, and then fetches/stores the data in a file
accessible to the ltsql 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.
Executing a command with PROGRAM
might be restricted
by the operating system's access control mechanisms, such as SELinux.
COPY FROM
will invoke any triggers and check
constraints on the destination table. However, it will not invoke rules.
For identity columns, the COPY FROM
command will always
write the column values provided in the input data, like
the INSERT
option OVERRIDING SYSTEM
VALUE
.
COPY
input and output is affected by
DateStyle
. To ensure portability to other
LightDB installations that might use
non-default DateStyle
settings,
DateStyle
should be set to ISO
before
using COPY TO
. It is also a good idea to avoid dumping
data with IntervalStyle
set to
sql_standard
, because negative interval values might be
misinterpreted by a server that has a different setting for
IntervalStyle
.
Input data is interpreted according to ENCODING
option or the current client encoding, and output data is encoded
in ENCODING
or the current client encoding, even
if the data does not pass through the client but is read from or
written to a file directly by the server.
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 might
amount to a considerable amount of wasted disk space if the failure
happened well into a large copy operation. You might wish to invoke
VACUUM
to recover the wasted space.
FORCE_NULL
and FORCE_NOT_NULL
can be used
simultaneously on the same column. This results in converting quoted
null strings to null values and unquoted null strings to empty strings.
When the text
format is used,
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.
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 (\
) can 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 option 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 rules used by
LightDB's standard text format, 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.
LightDB's COPY
handles this by quoting.
A NULL
is output as the NULL
parameter string
and is not quoted, while a non-NULL
value matching the
NULL
parameter string is quoted. For example, with the
default settings, a NULL
is written as an unquoted empty
string, while an empty string data value is written with double quotes
(""
). Reading values follows similar rules. You can
use FORCE_NOT_NULL
to prevent NULL
input
comparisons for specific columns. You can also use
FORCE_NULL
to convert quoted null string data values to
NULL
.
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
format, 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
LightDB.
CSV format 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-format 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 binary
format option causes all data to be
stored/read as binary format rather than as text. It is
somewhat faster than the text and CSV
formats,
but a binary-format file is less portable across machine architectures and
LightDB versions.
Also, the binary format is very data type specific; for example
it will not work to output binary data from a smallint
column
and read it into an integer
column, even though that would work
fine in text format.
The binary
file format consists
of a file header, zero or more tuples containing the row data, and
a file trailer. Headers and data are 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. Oid system columns are not supported in LightDB anymore, but the format still contains the indicator.
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 binary-format file are assumed to be in binary format (format code one). It is anticipated that a future extension might 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 LightDB 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. Note that oid system columns are not supported in current versions of LightDB.
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 (DELIMITER '|');
The following example copies a table to the client
using the vertical bar (ABC
) as the field delimiter:
COPY country TO STDOUT (DELIMITER 'ABC');
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';
To copy into a compressed file, you can pipe the output through an external compression program:
COPY country TO PROGRAM 'gzip > /usr1/proj/bray/sql/country_data.gz';
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 is supported:
COPYtable_name
[ (column_name
[, ...] ) ] FROM { 'filename
' | STDIN } [ [ WITH ] [ BINARY ] [ DELIMITER [ AS ] 'delimiter_character
' ] [ NULL [ AS ] 'null_string
' ] [ CSV [ HEADER ] [ QUOTE [ AS ] 'quote_character
' ] [ ESCAPE [ AS ] 'escape_character
' ] [ FORCE NOT NULLcolumn_name
[, ...] ] ] ] COPY {table_name
[ (column_name
[, ...] ) ] | (query
) } TO { 'filename
' | STDOUT } [ [ WITH ] [ BINARY ] [ DELIMITER [ AS ] 'delimiter_character
' ] [ NULL [ AS ] 'null_string
' ] [ CSV [ HEADER ] [ QUOTE [ AS ] 'quote_character
' ] [ ESCAPE [ AS ] 'escape_character
' ] [ FORCE QUOTE {column_name
[, ...] | * } ] ] ]
Note that in this syntax, BINARY
and CSV
are
treated as independent keywords, not as arguments of a FORMAT
option.
The following syntax is also supported:
COPY [ BINARY ]table_name
FROM { 'filename
' | STDIN } [ [USING] DELIMITERS 'delimiter_character
' ] [ WITH NULL AS 'null_string
' ] COPY [ BINARY ]table_name
TO { 'filename
' | STDOUT } [ [USING] DELIMITERS 'delimiter_character
' ] [ WITH NULL AS 'null_string
' ]