CREATE FOREIGN TABLE(7)           PostgreSQL 12.3 Documentation           CREATE FOREIGN TABLE(7)



NAME
       CREATE_FOREIGN_TABLE - define a new foreign table

SYNOPSIS
       CREATE FOREIGN TABLE [ IF NOT EXISTS ] table_name ( [
         { column_name data_type [ OPTIONS ( option 'value' [, ... ] ) ] [ COLLATE collation ] [ column_constraint [ ... ] ]
           | table_constraint }
           [, ... ]
       ] )
       [ INHERITS ( parent_table [, ... ] ) ]
         SERVER server_name
       [ OPTIONS ( option 'value' [, ... ] ) ]

       CREATE FOREIGN TABLE [ IF NOT EXISTS ] table_name
         PARTITION OF parent_table [ (
         { column_name [ WITH OPTIONS ] [ column_constraint [ ... ] ]
           | table_constraint }
           [, ... ]
       ) ] partition_bound_spec
         SERVER server_name
       [ OPTIONS ( option 'value' [, ... ] ) ]

       where column_constraint is:

       [ CONSTRAINT constraint_name ]
       { NOT NULL |
         NULL |
         CHECK ( expression ) [ NO INHERIT ] |
         DEFAULT default_expr |
         GENERATED ALWAYS AS ( generation_expr ) STORED }

       and table_constraint is:

       [ CONSTRAINT constraint_name ]
       CHECK ( expression ) [ NO INHERIT ]

DESCRIPTION
       CREATE FOREIGN TABLE creates a new foreign table in the current database. The table will
       be owned by the user issuing the command.

       If a schema name is given (for example, CREATE FOREIGN TABLE myschema.mytable ...) then
       the table is created in the specified schema. Otherwise it is created in the current
       schema. The name of the foreign table must be distinct from the name of any other foreign
       table, table, sequence, index, view, or materialized view in the same schema.

       CREATE FOREIGN TABLE also automatically creates a data type that represents the composite
       type corresponding to one row of the foreign table. Therefore, foreign tables cannot have
       the same name as any existing data type in the same schema.

       If PARTITION OF clause is specified then the table is created as a partition of
       parent_table with specified bounds.

       To be able to create a foreign table, you must have USAGE privilege on the foreign server,
       as well as USAGE privilege on all column types used in the table.

PARAMETERS
       IF NOT EXISTS
           Do not throw an error if a relation with the same name already exists. A notice is
           issued in this case. Note that there is no guarantee that the existing relation is
           anything like the one that would have been created.

       table_name
           The name (optionally schema-qualified) of the table to be created.

       column_name
           The name of a column to be created in the new table.

       data_type
           The data type of the column. This can include array specifiers. For more information
           on the data types supported by PostgreSQL, refer to Chapter 8.

       COLLATE collation
           The COLLATE clause assigns a collation to the column (which must be of a collatable
           data type). If not specified, the column data type's default collation is used.

       INHERITS ( parent_table [, ... ] )
           The optional INHERITS clause specifies a list of tables from which the new foreign
           table automatically inherits all columns. Parent tables can be plain tables or foreign
           tables. See the similar form of CREATE TABLE (CREATE_TABLE(7)) for more details.

       PARTITION OF parent_table FOR VALUES partition_bound_spec
           This form can be used to create the foreign table as partition of the given parent
           table with specified partition bound values. See the similar form of CREATE TABLE
           (CREATE_TABLE(7)) for more details. Note that it is currently not allowed to create
           the foreign table as a partition of the parent table if there are UNIQUE indexes on
           the parent table. (See also ALTER TABLE ATTACH PARTITION.)

       CONSTRAINT constraint_name
           An optional name for a column or table constraint. If the constraint is violated, the
           constraint name is present in error messages, so constraint names like col must be
           positive can be used to communicate helpful constraint information to client
           applications. (Double-quotes are needed to specify constraint names that contain
           spaces.) If a constraint name is not specified, the system generates a name.

       NOT NULL
           The column is not allowed to contain null values.

       NULL
           The column is allowed to contain null values. This is the default.

           This clause is only provided for compatibility with non-standard SQL databases. Its
           use is discouraged in new applications.

       CHECK ( expression ) [ NO INHERIT ]
           The CHECK clause specifies an expression producing a Boolean result which each row in
           the foreign table is expected to satisfy; that is, the expression should produce TRUE
           or UNKNOWN, never FALSE, for all rows in the foreign table. A check constraint
           specified as a column constraint should reference that column's value only, while an
           expression appearing in a table constraint can reference multiple columns.

           Currently, CHECK expressions cannot contain subqueries nor refer to variables other
           than columns of the current row. The system column tableoid may be referenced, but not
           any other system column.

           A constraint marked with NO INHERIT will not propagate to child tables.

       DEFAULT default_expr
           The DEFAULT clause assigns a default data value for the column whose column definition
           it appears within. The value is any variable-free expression (subqueries and
           cross-references to other columns in the current table are not allowed). The data type
           of the default expression must match the data type of the column.

           The default expression will be used in any insert operation that does not specify a
           value for the column. If there is no default for a column, then the default is null.

       GENERATED ALWAYS AS ( generation_expr ) STORED
           This clause creates the column as a generated column. The column cannot be written to,
           and when read the result of the specified expression will be returned.

           The keyword STORED is required to signify that the column will be computed on write.
           (The computed value will be presented to the foreign-data wrapper for storage and must
           be returned on reading.)

           The generation expression can refer to other columns in the table, but not other
           generated columns. Any functions and operators used must be immutable. References to
           other tables are not allowed.

       server_name
           The name of an existing foreign server to use for the foreign table. For details on
           defining a server, see CREATE SERVER (CREATE_SERVER(7)).

       OPTIONS ( option 'value' [, ...] )
           Options to be associated with the new foreign table or one of its columns. The allowed
           option names and values are specific to each foreign data wrapper and are validated
           using the foreign-data wrapper's validator function. Duplicate option names are not
           allowed (although it's OK for a table option and a column option to have the same
           name).

NOTES
       Constraints on foreign tables (such as CHECK or NOT NULL clauses) are not enforced by the
       core PostgreSQL system, and most foreign data wrappers do not attempt to enforce them
       either; that is, the constraint is simply assumed to hold true. There would be little
       point in such enforcement since it would only apply to rows inserted or updated via the
       foreign table, and not to rows modified by other means, such as directly on the remote
       server. Instead, a constraint attached to a foreign table should represent a constraint
       that is being enforced by the remote server.

       Some special-purpose foreign data wrappers might be the only access mechanism for the data
       they access, and in that case it might be appropriate for the foreign data wrapper itself
       to perform constraint enforcement. But you should not assume that a wrapper does that
       unless its documentation says so.

       Although PostgreSQL does not attempt to enforce constraints on foreign tables, it does
       assume that they are correct for purposes of query optimization. If there are rows visible
       in the foreign table that do not satisfy a declared constraint, queries on the table might
       produce incorrect answers. It is the user's responsibility to ensure that the constraint
       definition matches reality.

       Similar considerations apply to generated columns. Stored generated columns are computed
       on insert or update on the local PostgreSQL server and handed to the foreign-data wrapper
       for writing out to the foreign data store, but it is not enforced that a query of the
       foreign table returns values for stored generated columns that are consistent with the
       generation expression. Again, this might result in incorrect query results.

       While rows can be moved from local partitions to a foreign-table partition (provided the
       foreign data wrapper supports tuple routing), they cannot be moved from a foreign-table
       partition to another partition.

EXAMPLES
       Create foreign table films, which will be accessed through the server film_server:

           CREATE FOREIGN TABLE films (
               code        char(5) NOT NULL,
               title       varchar(40) NOT NULL,
               did         integer NOT NULL,
               date_prod   date,
               kind        varchar(10),
               len         interval hour to minute
           )
           SERVER film_server;

       Create foreign table measurement_y2016m07, which will be accessed through the server
       server_07, as a partition of the range partitioned table measurement:

           CREATE FOREIGN TABLE measurement_y2016m07
               PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')
               SERVER server_07;

COMPATIBILITY
       The CREATE FOREIGN TABLE command largely conforms to the SQL standard; however, much as
       with CREATE TABLE, NULL constraints and zero-column foreign tables are permitted. The
       ability to specify column default values is also a PostgreSQL extension. Table
       inheritance, in the form defined by PostgreSQL, is nonstandard.

SEE ALSO
       ALTER FOREIGN TABLE (ALTER_FOREIGN_TABLE(7)), DROP FOREIGN TABLE (DROP_FOREIGN_TABLE(7)),
       CREATE TABLE (CREATE_TABLE(7)), CREATE SERVER (CREATE_SERVER(7)), IMPORT FOREIGN SCHEMA
       (IMPORT_FOREIGN_SCHEMA(7))



PostgreSQL 12.3                                2020                       CREATE FOREIGN TABLE(7)