Defines a new external table.
CREATE [READABLE] EXTERNAL [TEMPORARY | TEMP] TABLE <table_name>
( <column_name> <data_type> [, ...] | LIKE <other_table >)
LOCATION ('file://<seghost>[:<port>]/<path>/<file>' [, ...])
| ('gpfdist://<filehost>[:<port>]/<file_pattern>[#transform=<trans_name>]'
[, ...]
| ('gpfdists://<filehost>[:<port>]/<file_pattern>[#transform=<trans_name>]'
[, ...])
| ('gphdfs://<hdfs_host>[:port]/<path>/<file>')
| ('pxf://<path-to-data>?<PROFILE>[&<custom-option>=<value>[...]]'))
| ('s3://<S3_endpoint>[:<port>]/<bucket_name>/[<S3_prefix>] [region=<S3-region>] [config=<config_file>]')
[ON MASTER]
FORMAT 'TEXT'
[( [HEADER]
[DELIMITER [AS] '<delimiter>' | 'OFF']
[NULL [AS] '<null string>']
[ESCAPE [AS] '<escape>' | 'OFF']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CSV'
[( [HEADER]
[QUOTE [AS] '<quote>']
[DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[FORCE NOT NULL <column> [, ...]]
[ESCAPE [AS] '<escape>']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'AVRO'
| 'PARQUET'
| 'CUSTOM' (Formatter=<<formatter_specifications>>)
[ ENCODING '<encoding>' ]
[ [LOG ERRORS [PERSISTENTLY]] SEGMENT REJECT LIMIT <count>
[ROWS | PERCENT] ]
CREATE [READABLE] EXTERNAL WEB [TEMPORARY | TEMP] TABLE <table_name>
( <column_name> <data_type> [, ...] | LIKE <other_table >)
LOCATION ('http://<webhost>[:<port>]/<path>/<file>' [, ...])
| EXECUTE '<command>' [ON ALL
| MASTER
| <number_of_segments>
| HOST ['<segment_hostname>']
| SEGMENT <segment_id> ]
FORMAT 'TEXT'
[( [HEADER]
[DELIMITER [AS] '<delimiter>' | 'OFF']
[NULL [AS] '<null string>']
[ESCAPE [AS] '<escape>' | 'OFF']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CSV'
[( [HEADER]
[QUOTE [AS] '<quote>']
[DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[FORCE NOT NULL <column> [, ...]]
[ESCAPE [AS] '<escape>']
[NEWLINE [ AS ] 'LF' | 'CR' | 'CRLF']
[FILL MISSING FIELDS] )]
| 'CUSTOM' (Formatter=<<formatter specifications>>)
[ ENCODING '<encoding>' ]
[ [LOG ERRORS [PERSISTENTLY]] SEGMENT REJECT LIMIT <count>
[ROWS | PERCENT] ]
CREATE WRITABLE EXTERNAL [TEMPORARY | TEMP] TABLE <table_name>
( <column_name> <data_type> [, ...] | LIKE <other_table >)
LOCATION('gpfdist://<outputhost>[:<port>]/<filename>[#transform=<trans_name>]'
[, ...])
| ('gpfdists://<outputhost>[:<port>]/<file_pattern>[#transform=<trans_name>]'
[, ...])
| ('gphdfs://<hdfs_host>[:port]/<path>')
FORMAT 'TEXT'
[( [DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[ESCAPE [AS] '<escape>' | 'OFF'] )]
| 'CSV'
[([QUOTE [AS] '<quote>']
[DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[FORCE QUOTE <column> [, ...]] | * ]
[ESCAPE [AS] '<escape>'] )]
| 'AVRO'
| 'PARQUET'
| 'CUSTOM' (Formatter=<<formatter specifications>>)
[ ENCODING '<write_encoding>' ]
[ DISTRIBUTED BY (<column>, [ ... ] ) | DISTRIBUTED RANDOMLY ]
CREATE WRITABLE EXTERNAL [TEMPORARY | TEMP] TABLE <table_name>
( <column_name> <data_type> [, ...] | LIKE <other_table >)
LOCATION('s3://<S3_endpoint>[:<port>]/<bucket_name>/[<S3_prefix>] [region=<S3-region>] [config=<config_file>]')
[ON MASTER]
FORMAT 'TEXT'
[( [DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[ESCAPE [AS] '<escape>' | 'OFF'] )]
| 'CSV'
[([QUOTE [AS] '<quote>']
[DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[FORCE QUOTE <column> [, ...]] | * ]
[ESCAPE [AS] '<escape>'] )]
CREATE WRITABLE EXTERNAL WEB [TEMPORARY | TEMP] TABLE <table_name>
( <column_name> <data_type> [, ...] | LIKE <other_table> )
EXECUTE '<command>' [ON ALL]
FORMAT 'TEXT'
[( [DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[ESCAPE [AS] '<escape>' | 'OFF'] )]
| 'CSV'
[([QUOTE [AS] '<quote>']
[DELIMITER [AS] '<delimiter>']
[NULL [AS] '<null string>']
[FORCE QUOTE <column> [, ...]] | * ]
[ESCAPE [AS] '<escape>'] )]
| 'CUSTOM' (Formatter=<<formatter specifications>>)
[ ENCODING '<write_encoding>' ]
[ DISTRIBUTED BY (<column>, [ ... ] ) | DISTRIBUTED RANDOMLY ]
CREATE EXTERNAL TABLE
or CREATE EXTERNAL WEB TABLE
creates a new readable external table definition in Greenplum Database. Readable external tables are typically used for fast, parallel data loading. Once an external table is defined, you can query its data directly (and in parallel) using SQL commands. For example, you can select, join, or sort external table data. You can also create views for external tables. DML operations (UPDATE
, INSERT
, DELETE
, or TRUNCATE
) are not allowed on readable external tables, and you cannot create indexes on readable external tables.
CREATE WRITABLE EXTERNAL TABLE
or CREATE WRITABLE EXTERNAL WEB TABLE
creates a new writable external table definition in Greenplum Database. Writable external tables are typically used for unloading data from the database into a set of files or named pipes. Writable external web tables can also be used to output data to an executable program. Writable external tables can also be used as output targets for Greenplum parallel MapReduce calculations. Once a writable external table is defined, data can be selected from database tables and inserted into the writable external table. Writable external tables only allow INSERT
operations – SELECT
, UPDATE
, DELETE
or TRUNCATE
are not allowed.
The main difference between regular external tables and external web tables is their data sources. Regular readable external tables access static flat files, whereas external web tables access dynamic data sources – either on a web server or by executing OS commands or scripts.
See Working with External Data for detailed information about working with external tables.
Creates a readable or writable external web table definition in Greenplum Database. There are two forms of readable external web tables – those that access files via the http://
protocol or those that access data by executing OS commands. Writable external web tables output data to an executable program that can accept an input stream of data. External web tables are not rescannable during query execution.
s3
protocol does not support external web tables. You can, however, create an external web table that executes a third-party tool to read data from or write data to S3 directly.
If specified, creates a temporary readable or writable external table definition in Greenplum Database. Temporary external tables exist in a special schema; you cannot specify a schema name when you create the table. Temporary external tables are automatically dropped at the end of a session.
LIKE
clause specifies a table from which the new external table automatically copies all column names, data types and Greenplum distribution policy. If the original table specifies any column constraints or default column values, those will not be copied over to the new external table definition.
If you use the gphdfs
protocol (deprecated) to read or write a file to a Hadoop file system (HDFS), refer to Specify gphdfs Protocol in an External Table Definition (Deprecated) for additional information about the gphdfs
protocol LOCATION
clause syntax.
If you use the pxf
protocol to access an external data source, refer to pxf:// Protocol for information about the pxf
protocol.
If you use the s3
protocol to read or write to S3, refer to About the S3 Protocol URL for additional information about the s3
protocol LOCATION
clause syntax.
For readable external tables, specifies the URI of the external data source(s) to be used to populate the external table or web table. Regular readable external tables allow the gpfdist
or file
protocols. External web tables allow the http
protocol. If port
is omitted, port 8080
is assumed for http
and gpfdist
protocols, and port 9000 for the gphdfs
protocol (deprecated). If using the gpfdist
protocol, the path
is relative to the directory from which gpfdist
is serving files (the directory specified when you started the gpfdist
program). Also, gpfdist
can use wildcards or other C-style pattern matching (for example, a whitespace character is [[:space:]]
) to denote multiple files in a directory. For example:
'gpfdist://filehost:8081/*'
'gpfdist://masterhost/my_load_file'
'file://seghost1/dbfast1/external/myfile.txt'
'http://intranet.example.com/finance/expenses.csv'
gpfdist
process or S3 protocol that will collect data output from the Greenplum segments and write it to one or more named files. For
gpfdist
the
path
is relative to the directory from which
gpfdist
is serving files (the directory specified when you started the
gpfdist
program). If multiple
gpfdist
locations are listed, the segments sending data will be evenly divided across the available output locations. For example:
'gpfdist://outputhost:8081/data1.out',
'gpfdist://outputhost:8081/data2.out'
gpfdist
locations listed as in the above example, half of the segments would send their output data to the
data1.out
file and the other half to the
data2.out
file.
#transform=trans\_name
, you can specify a transform to apply when loading or extracting data. The trans_name is the name of the transform in the YAML configuration file you specify with the you run the
gpfdist
utility. For information about specifying a transform, see
gpfdist
in the
Greenplum Utility Guide.
Restricts all table-related operations to the Greenplum master segment. Permitted only on readable and writable external tables created with the s3
or custom protocols. The gpfdist
, gpfdists
, gphdfs
(deprecated), pxf
, and file
protocols do not support ON MASTER
.
Note: Be aware of potential resource impacts when reading from or writing to external tables you create with the ON MASTER
clause. You may encounter performance issues when you restrict table operations solely to the Greenplum master segment.
Allowed for readable external web tables or writable external tables only. For readable external web tables, specifies the OS command to be executed by the segment instances. The command can be a single OS command or a script. The ON
clause is used to specify which segment instances will execute the given command.
gpadmin
).**Note:** Logging is not supported for external web tables when the `ON MASTER` clause is specified.
gpadmin
).-1
.For writable external tables, the command specified in the EXECUTE
clause must be prepared to have data piped into it. Since all segments that have data to send will write their output to the specified command or program, the only available option for the ON
clause is ON ALL
.
When the FORMAT
clause identfies delimited text (TEXT
) or comma separated values (CSV
) format, formatting options are similar to those available with the PostgreSQL COPY command. If the data in the file does not use the default column delimiter, escape character, null string and so on, you must specify the additional formatting options so that the data in the external file is read correctly by Greenplum Database. For information about using a custom format, see "Loading and Unloading Data" in the Greenplum Database Administrator Guide.
The AVRO
and PARQUET
formats are supported only when you specify the gphdfs
protocol (deprecated). Refer to Accessing HDFS Data with gphdfs (Deprecated) for detailed information about the gphdfs
protocol FORMAT
clause syntax.
pxf
protocol to access an external data source, refer to
Accessing External Data with PXF for information about using PXF.
Specifies a custom data format. The formatter_specification specifies the function to use to format the data, followed by comma-separated parameters to the formatter function. The length of the formatter specification, the string including Formatter=
, can be up to approximately 50K bytes.
If you use the pxf
protocol to access an external data source, refer to Accessing External Data with PXF for information about using PXF.
Specifies a single ASCII character that separates columns within each row (line) of data. The default is a tab character in TEXT
mode, a comma in CSV
mode. In TEXT
mode for readable external tables, the delimiter can be set to OFF
for special use cases in which unstructured data is loaded into a single-column table.
s3
protocol, the delimiter cannot be a newline character (
\n
) or a carriage return character (
\r
).
Specifies the string that represents a NULL
value. The default is \N
(backslash-N) in TEXT
mode, and an empty value with no quotations in CSV
mode. You might prefer an empty string even in TEXT
mode for cases where you do not want to distinguish NULL
values from empty strings. When using external and web tables, any data item that matches this string will be considered a NULL
value.
As an example for the text
format, this FORMAT
clause can be used to specify that the string of two single quotes (''
) is a NULL
value.
FORMAT 'text' (delimiter ',' null '\'\'\'\'' )
\n
,
\t
,
\100
, and so on) and for escaping data characters that might otherwise be taken as row or column delimiters. Make sure to choose an escape character that is not used anywhere in your actual column data. The default escape character is a \ (backslash) for text-formatted files and a
"
(double quote) for csv-formatted files, however it is possible to specify another character to represent an escape. It is also possible to deactivate escaping in text-formatted files by specifying the value
'OFF'
as the escape value. This is very useful for data such as text-formatted web log data that has many embedded backslashes that are not intended to be escapes.
LF
(Line feed, 0x0A),
CR
(Carriage return, 0x0D), or
CRLF
(Carriage return plus line feed, 0x0D 0x0A). If not specified, a Greenplum Database segment will detect the newline type by looking at the first row of data it receives and using the first newline type encountered.
For readable external tables, specifies that the first line in the data file(s) is a header row (contains the names of the table columns) and should not be included as data for the table. If using multiple data source files, all files must have a header row.
For the s3
protocol, the column names in the header row cannot contain a newline character (\n
) or a carriage return (\r
).
pxf
protocol does not support the
HEADER
formatting option.
CSV
mode. The default is double-quote (
"
).
CSV
mode, processes each specified column as though it were quoted and hence not a
NULL
value. For the default null string in
CSV
mode (nothing between two delimiters), this causes missing values to be evaluated as zero-length strings.
CSV
mode for writable external tables, forces quoting to be used for all non-
NULL
values in each specified column. If
*
is specified then non-
NULL
values will be quoted in all columns.
NULL
output is never quoted.
TEXT
and
CSV
mode for readable external tables, specifying
FILL MISSING FIELDS
will set missing trailing field values to
NULL
(instead of reporting an error) when a row of data has missing data fields at the end of a line or row. Blank rows, fields with a
NOT NULL
constraint, and trailing delimiters on a line will still report an error.
'SQL_ASCII'
), an integer encoding number, or
DEFAULT
to use the default client encoding. See
Character Set Support.
This is an optional clause that can precede a SEGMENT REJECT LIMIT
clause to log information about rows with formatting errors. The error log data is stored internally. If error log data exists for a specified external table, new data is appended to existing error log data. The error log data is not replicated to mirror segments.
The data is deleted when the external table is dropped unless you specify the keyword PERSISTENTLY
. If the keyword is specified, the log data persists after the external table is dropped.
The error log data is accessed with the Greenplum Database built-in SQL function gp_read_error_log()
, or with the SQL function gp_read_persistent_error_log()
if the PERSISTENTLY
keyword is specified.
If you use the PERSISTENTLY
keyword, you must install the functions that manage the persistent error log information.
Runs a COPY FROM
operation in single row error isolation mode. If the input rows have format errors they will be discarded provided that the reject limit count is not reached on any Greenplum segment instance during the load operation. The reject limit count can be specified as number of rows (the default) or percentage of total rows (1-100). If PERCENT
is used, each segment starts calculating the bad row percentage only after the number of rows specified by the parameter gp_reject_percent_threshold
has been processed. The default for gp_reject_percent_threshold
is 300 rows. Constraint errors such as violation of a NOT NULL
, CHECK
, or UNIQUE
constraint will still be handled in "all-or-nothing" input mode. If the limit is not reached, all good rows will be loaded and any error rows discarded.
SEGMENT REJECT LIMIT
is not triggered first or is not specified. If the first 1000 rows are rejected, the
COPY
operation is stopped and rolled back.
The limit for the number of initial rejected rows can be changed with the Greenplum Database server configuration parameter gp_initial_bad_row_limit
. See Server Configuration Parameters for information about the parameter.
INSERT INTO wex\_table SELECT * FROM source\_table
, the rows that are unloaded can be sent directly from the segments to the output location if the two tables have the same hash distribution policy.
Start the gpfdist
file server program in the background on port 8081
serving files from directory /var/data/staging
:
gpfdist -p 8081 -d /var/data/staging -l /home/<gpadmin>/log &
Create a readable external table named ext_customer
using the gpfdist
protocol and any text formatted files (*.txt
) found in the gpfdist
directory. The files are formatted with a pipe (|
) as the column delimiter and an empty space as NULL
. Also access the external table in single row error isolation mode:
CREATE EXTERNAL TABLE ext_customer
(id int, name text, sponsor text)
LOCATION ( 'gpfdist://filehost:8081/*.txt' )
FORMAT 'TEXT' ( DELIMITER '|' NULL ' ')
LOG ERRORS SEGMENT REJECT LIMIT 5;
Create the same readable external table definition as above, but with CSV formatted files:
CREATE EXTERNAL TABLE ext_customer
(id int, name text, sponsor text)
LOCATION ( 'gpfdist://filehost:8081/*.csv' )
FORMAT 'CSV' ( DELIMITER ',' );
Create a readable external table named ext_expenses
using the file
protocol and several CSV formatted files that have a header row:
CREATE EXTERNAL TABLE ext_expenses (name text, date date,
amount float4, category text, description text)
LOCATION (
'file://seghost1/dbfast/external/expenses1.csv',
'file://seghost1/dbfast/external/expenses2.csv',
'file://seghost2/dbfast/external/expenses3.csv',
'file://seghost2/dbfast/external/expenses4.csv',
'file://seghost3/dbfast/external/expenses5.csv',
'file://seghost3/dbfast/external/expenses6.csv'
)
FORMAT 'CSV' ( HEADER );
Create a readable external web table that executes a script once per segment host:
CREATE EXTERNAL WEB TABLE log_output (linenum int, message
text) EXECUTE '/var/load_scripts/get_log_data.sh' ON HOST
FORMAT 'TEXT' (DELIMITER '|');
Create a writable external table named sales_out
that uses gpfdist
to write output data to a file named sales.out
. The files are formatted with a pipe (|
) as the column delimiter and an empty space as NULL
.
CREATE WRITABLE EXTERNAL TABLE sales_out (LIKE sales)
LOCATION ('gpfdist://etl1:8081/sales.out')
FORMAT 'TEXT' ( DELIMITER '|' NULL ' ')
DISTRIBUTED BY (txn_id);
Create a writable external web table that pipes output data received by the segments to an executable script named to_adreport_etl.sh
:
CREATE WRITABLE EXTERNAL WEB TABLE campaign_out
(LIKE campaign)
EXECUTE '/var/unload_scripts/to_adreport_etl.sh'
FORMAT 'TEXT' (DELIMITER '|');
Use the writable external table defined above to unload selected data:
INSERT INTO campaign_out SELECT * FROM campaign WHERE
customer_id=123;
When you specify the LOG ERRORS
clause, Greenplum Database captures errors that occur while reading the external table data. For information about the error log format, see Viewing Bad Rows in the Error Log.
You can view and manage the captured error log data. The functions to manage log data depend on whether the data is persistent (the PERSISTENTLY
keyword is used with the LOG ERRORS
clause).
Functions that manage non-persistent error log data from external tables that were defined without the PERSISTENTLY
keyword.
The built-in SQL function gp_read_error_log('table\_name')
displays error log information for an external table. This example displays the error log data from the external table ext_expenses
.
SELECT * from gp_read_error_log('ext_expenses');
The function returns no data if you created the external table with the LOG ERRORS PERSISTENTLY
clause, or if the external table does not exist.
The built-in SQL function gp_truncate_error_log('table\_name')
deletes the error log data for table_name. This example deletes the error log data captured from the external table ext_expenses
:
SELECT gp_truncate_error_log('ext_expenses');
Dropping the table also deletes the table's log data. The function does not truncate log data if the external table is defined with the LOG ERRORS PERSISTENTLY
clause.
The function returns FALSE
if the table does not exist.
Functions that manage persistent error log data from external tables that were defined with the PERSISTENTLY
keyword.
Note: The functions that manage persistent error log data from external tables are defined in the file $GPHOME/share/postgresql/contrib/gpexterrorhandle.sql
. The functions must be installed in the databases that use persistent error log data from an external table. This psql
command installs the functions into the database testdb
.
psql -d test -U gpadmin -f $GPHOME/share/postgresql/contrib/gpexterrorhandle.sql
The SQL function gp_read_persistent_error_log('table\_name')
displays persistent log data for an external table.
The function returns no data if you created the external table without the PERSISTENTLY
keyword. The function returns persistent log data for an external table even after the table has been dropped.
The SQL function gp_truncate_persistent_error_log('table\_name')
truncates persistent log data for a table.
For persistent log data, you must manually delete the data. Dropping the external table does not delete persistent log data.
These items apply to both non-persistent and persistent error log data and the related functions.
gp_read_*
functions require SELECT
privilege on the table.gp_truncate_*
functions require owner privilege on the table.*
wildcard character to delete error log information for existing tables in the current database. Specify the string *.*
to delete all database error log information, including error log information that was not deleted due to previous database issues. If *
is specified, database owner privilege is required. If *.*
is specified, operating system super-user privilege is required. Non-persistent and persistent error log data must be deleted with their respective gp_truncate_*
functions.When multiple Greenplum Database external tables are defined with the gpfdist
, gpfdists
, or file
protocol and access the same named pipe a Linux system, Greenplum Database restricts access to the named pipe to a single reader. An error is returned if a second reader attempts to access the named pipe.
CREATE EXTERNAL TABLE
is a Greenplum Database extension. The SQL standard makes no provisions for external tables.
CREATE TABLE AS, CREATE TABLE, COPY, SELECT INTO, INSERT
Parent topic: SQL Command Reference