3bd8445b创建于 1月27日历史提交

file_fdw

The file_fdw module provides the external data wrapper file_fdw, which can be used to access data files in the file system of a server. The format of the data files must be readable by the COPY FROM command. For details, see COPY. file_fdw is only used to access readable data files, but cannot write data to the data files.

By default, the file_fdw is compiled in openGauss. During database initialization, the plug-in is created in the pg_catalog schema.

The server and foreign table corresponding to file_fdw can be created only by the initial user of the database or the O&M administrator who enables the O&M mode.

When you create a foreign table using file_fdw, you can add the following options:

filename

File to be read. This parameter is mandatory and must be an absolute path.
format

File format of the remote server, which is the same as the FORMAT option in the COPY statement. The value can be text, csv, or binary.
header

Whether the specified file has a header, which is the same as the HEADER option of the COPY statement.
delimiter

File delimiter, which is the same as the DELIMITER option of the COPY statement.
quote

Quote character of a file, which is the same as the QUOTE option of the COPY statement.
escape

Escape character of a file, which is the same as the ESCAPE option of the COPY statement.
null

Null string of a file, which is the same as the NULL option of the COPY statement.
encoding

Encoding of a file, which is the same as the ENCODING option of the COPY statement.
force_not_null

File-level null option, which is a Boolean option. If it is true, the value of the declared field cannot be an empty string. This option is the same as the FORCE_NOT_NULL option of the COPY statement.

NOTE

file_fdw does not support the OIDS and FORCE_QUOTE options of the COPY statement.
These options can only be declared for a foreign table or the columns of the foreign table, not for the file_fdw itself, nor for the server or user mapping that uses file_fdw.
To modify table-level options, you must obtain the system administrator role permissions. For security reasons, only the system administrator can determine the files to be read.
For an external table that uses file_fdw, EXPLAIN displays the name and size (in bytes) of the file to be read. If the keyword COSTS OFF is specified, the file size is not displayed.

Using file_fdw

To create a server object, use CREATE SERVER.
To create a user mapping, use CREATE USER MAPPING.
To create a foreign table, use CREATE FOREIGN TABLE.
NOTE
- The structure of the foreign table must be consistent with the data in the specified file.
- When a foreign table is queried, no write operation is allowed.
To drop a foreign table, use DROP FOREIGN TABLE.
To drop a user mapping, use DROP USER MAPPING.
To drop a server object, use DROP SERVER.

Precautions

To use file_fdw, you need to specify the file to be read. Prepare the file and grant the read permission on the file for the database to access the file.
DROP EXTENSION file_fdw is not supported.