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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>CREATE FOREIGN TABLE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER" /><link rel="next" href="sql-createfunction.html" title="CREATE FUNCTION" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE FOREIGN TABLE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-createfunction.html" title="CREATE FUNCTION">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-CREATEFOREIGNTABLE"><div class="titlepage"></div><a id="id-1.9.3.66.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE FOREIGN TABLE</span></h2><p>CREATE FOREIGN TABLE — define a new foreign table</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
CREATE FOREIGN TABLE [ IF NOT EXISTS ] <em class="replaceable"><code>table_name</code></em> ( [
{ <em class="replaceable"><code>column_name</code></em> <em class="replaceable"><code>data_type</code></em> [ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ] [ COLLATE <em class="replaceable"><code>collation</code></em> ] [ <em class="replaceable"><code>column_constraint</code></em> [ ... ] ]
| <em class="replaceable"><code>table_constraint</code></em> }
[, ... ]
] )
[ INHERITS ( <em class="replaceable"><code>parent_table</code></em> [, ... ] ) ]
SERVER <em class="replaceable"><code>server_name</code></em>
[ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]
CREATE FOREIGN TABLE [ IF NOT EXISTS ] <em class="replaceable"><code>table_name</code></em>
PARTITION OF <em class="replaceable"><code>parent_table</code></em> [ (
{ <em class="replaceable"><code>column_name</code></em> [ WITH OPTIONS ] [ <em class="replaceable"><code>column_constraint</code></em> [ ... ] ]
| <em class="replaceable"><code>table_constraint</code></em> }
[, ... ]
) ]
{ FOR VALUES <em class="replaceable"><code>partition_bound_spec</code></em> | DEFAULT }
SERVER <em class="replaceable"><code>server_name</code></em>
[ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]
<span class="phrase">where <em class="replaceable"><code>column_constraint</code></em> is:</span>
[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]
{ NOT NULL |
NULL |
CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] |
DEFAULT <em class="replaceable"><code>default_expr</code></em> |
GENERATED ALWAYS AS ( <em class="replaceable"><code>generation_expr</code></em> ) STORED }
<span class="phrase">and <em class="replaceable"><code>table_constraint</code></em> is:</span>
[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]
CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ]
<span class="phrase">and <em class="replaceable"><code>partition_bound_spec</code></em> is:</span>
IN ( <em class="replaceable"><code>partition_bound_expr</code></em> [, ...] ) |
FROM ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] )
TO ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] ) |
WITH ( MODULUS <em class="replaceable"><code>numeric_literal</code></em>, REMAINDER <em class="replaceable"><code>numeric_literal</code></em> )
</pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-DESCRIPTION"><h2>Description</h2><p>
<code class="command">CREATE FOREIGN TABLE</code> creates a new foreign table
in the current database. The table will be owned by the user issuing the
command.
</p><p>
If a schema name is given (for example, <code class="literal">CREATE FOREIGN TABLE
myschema.mytable ...</code>) 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 relation (table, sequence, index, view,
materialized view, or foreign table) in the same schema.
</p><p>
<code class="command">CREATE FOREIGN TABLE</code> 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.
</p><p>
If <code class="literal">PARTITION OF</code> clause is specified then the table is
created as a partition of <code class="literal">parent_table</code> with specified
bounds.
</p><p>
To be able to create a foreign table, you must have <code class="literal">USAGE</code>
privilege on the foreign server, as well as <code class="literal">USAGE</code>
privilege on all column types used in the table.
</p></div><div class="refsect1" id="id-1.9.3.66.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">IF NOT EXISTS</code></span></dt><dd><p>
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.
</p></dd><dt><span class="term"><em class="replaceable"><code>table_name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of the table to be created.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>
The name of a column to be created in the new table.
</p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p>
The data type of the column. This can include array
specifiers. For more information on the data types supported by
<span class="productname">PostgreSQL</span>, refer to <a class="xref" href="datatype.html" title="Chapter 8. Data Types">Chapter 8</a>.
</p></dd><dt><span class="term"><code class="literal">COLLATE <em class="replaceable"><code>collation</code></em></code></span></dt><dd><p>
The <code class="literal">COLLATE</code> 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.
</p></dd><dt><span class="term"><code class="literal">INHERITS ( <em class="replaceable"><code>parent_table</code></em> [, ... ] )</code></span></dt><dd><p>
The optional <code class="literal">INHERITS</code> 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
<a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> for more details.
</p></dd><dt><span class="term"><code class="literal">PARTITION OF <em class="replaceable"><code>parent_table</code></em> { FOR VALUES <em class="replaceable"><code>partition_bound_spec</code></em> | DEFAULT }</code></span></dt><dd><p>
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
<a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> 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 <code class="literal">UNIQUE</code>
indexes on the parent table. (See also
<a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER TABLE ATTACH PARTITION</code></a>.)
</p></dd><dt><span class="term"><code class="literal">CONSTRAINT <em class="replaceable"><code>constraint_name</code></em></code></span></dt><dd><p>
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 <code class="literal">col must be positive</code> 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.
</p></dd><dt><span class="term"><code class="literal">NOT NULL</code></span></dt><dd><p>
The column is not allowed to contain null values.
</p></dd><dt><span class="term"><code class="literal">NULL</code></span></dt><dd><p>
The column is allowed to contain null values. This is the default.
</p><p>
This clause is only provided for compatibility with
non-standard SQL databases. Its use is discouraged in new
applications.
</p></dd><dt><span class="term"><code class="literal">CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] </code></span></dt><dd><p>
The <code class="literal">CHECK</code> 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.
</p><p>
Currently, <code class="literal">CHECK</code> expressions cannot contain
subqueries nor refer to variables other than columns of the
current row. The system column <code class="literal">tableoid</code>
may be referenced, but not any other system column.
</p><p>
A constraint marked with <code class="literal">NO INHERIT</code> will not propagate to
child tables.
</p></dd><dt><span class="term"><code class="literal">DEFAULT
<em class="replaceable"><code>default_expr</code></em></code></span></dt><dd><p>
The <code class="literal">DEFAULT</code> 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.
</p><p>
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.
</p></dd><dt><span class="term"><code class="literal">GENERATED ALWAYS AS ( <em class="replaceable"><code>generation_expr</code></em> ) STORED</code><a id="id-1.9.3.66.6.2.13.1.2" class="indexterm"></a></span></dt><dd><p>
This clause creates the column as a <em class="firstterm">generated
column</em>. The column cannot be written to, and when read the
result of the specified expression will be returned.
</p><p>
The keyword <code class="literal">STORED</code> 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.)
</p><p>
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.
</p></dd><dt><span class="term"><em class="replaceable"><code>server_name</code></em></span></dt><dd><p>
The name of an existing foreign server to use for the foreign table.
For details on defining a server, see <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>.
</p></dd><dt><span class="term"><code class="literal">OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ...] )</code></span></dt><dd><p>
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).
</p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.66.7"><h2>Notes</h2><p>
Constraints on foreign tables (such as <code class="literal">CHECK</code>
or <code class="literal">NOT NULL</code> clauses) are not enforced by the
core <span class="productname">PostgreSQL</span> 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.
</p><p>
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.
</p><p>
Although <span class="productname">PostgreSQL</span> 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 errors or incorrect answers. It is the user's
responsibility to ensure that the constraint definition matches
reality.
</p><div class="caution"><h3 class="title">Caution</h3><p>
When a foreign table is used as a partition of a partitioned table,
there is an implicit constraint that its contents must satisfy the
partitioning rule. Again, it is the user's responsibility to ensure
that that is true, which is best done by installing a matching
constraint on the remote server.
</p></div><p>
Within a partitioned table containing foreign-table partitions,
an <code class="command">UPDATE</code> that changes the partition key value can
cause a row to be moved from a local partition to a foreign-table
partition, provided the foreign data wrapper supports tuple routing.
However, it is not currently possible to move a row from a
foreign-table partition to another partition.
An <code class="command">UPDATE</code> that would require doing that will fail
due to the partitioning constraint, assuming that that is properly
enforced by the remote server.
</p><p>
Similar considerations apply to generated columns. Stored generated
columns are computed on insert or update on the local
<span class="productname">PostgreSQL</span> 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.
</p></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-EXAMPLES"><h2>Examples</h2><p>
Create foreign table <code class="structname">films</code>, which will be accessed through
the server <code class="structname">film_server</code>:
</p><pre class="programlisting">
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;
</pre><p>
Create foreign table <code class="structname">measurement_y2016m07</code>, which will be
accessed through the server <code class="structname">server_07</code>, as a partition
of the range partitioned table <code class="structname">measurement</code>:
</p><pre class="programlisting">
CREATE FOREIGN TABLE measurement_y2016m07
PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')
SERVER server_07;
</pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-COMPATIBILITY"><h2>Compatibility</h2><p>
The <code class="command">CREATE FOREIGN TABLE</code> command largely conforms to the
<acronym class="acronym">SQL</acronym> standard; however, much as with
<a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>,
<code class="literal">NULL</code> constraints and zero-column foreign tables are permitted.
The ability to specify column default values is also
a <span class="productname">PostgreSQL</span> extension. Table inheritance, in the form
defined by <span class="productname">PostgreSQL</span>, is nonstandard.
</p></div><div class="refsect1" id="id-1.9.3.66.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-alterforeigntable.html" title="ALTER FOREIGN TABLE"><span class="refentrytitle">ALTER FOREIGN TABLE</span></a>, <a class="xref" href="sql-dropforeigntable.html" title="DROP FOREIGN TABLE"><span class="refentrytitle">DROP FOREIGN TABLE</span></a>, <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a>, <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>, <a class="xref" href="sql-importforeignschema.html" title="IMPORT FOREIGN SCHEMA"><span class="refentrytitle">IMPORT FOREIGN SCHEMA</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createfunction.html" title="CREATE FUNCTION">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE FOREIGN DATA WRAPPER </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> CREATE FUNCTION</td></tr></table></div></body></html>