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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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">3CREATE FOREIGN TABLE [ IF NOT EXISTS ] <em class="replaceable"><code>table_name</code></em> ( [4  { <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> [ ... ] ]5    | <em class="replaceable"><code>table_constraint</code></em> }6    [, ... ]7] )8[ INHERITS ( <em class="replaceable"><code>parent_table</code></em> [, ... ] ) ]9  SERVER <em class="replaceable"><code>server_name</code></em>10[ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]11 12CREATE FOREIGN TABLE [ IF NOT EXISTS ] <em class="replaceable"><code>table_name</code></em>13  PARTITION OF <em class="replaceable"><code>parent_table</code></em> [ (14  { <em class="replaceable"><code>column_name</code></em> [ WITH OPTIONS ] [ <em class="replaceable"><code>column_constraint</code></em> [ ... ] ]15    | <em class="replaceable"><code>table_constraint</code></em> }16    [, ... ]17) ]18{ FOR VALUES <em class="replaceable"><code>partition_bound_spec</code></em> | DEFAULT }19  SERVER <em class="replaceable"><code>server_name</code></em>20[ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]21 22<span class="phrase">where <em class="replaceable"><code>column_constraint</code></em> is:</span>23 24[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]25{ NOT NULL |26  NULL |27  CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] |28  DEFAULT <em class="replaceable"><code>default_expr</code></em> |29  GENERATED ALWAYS AS ( <em class="replaceable"><code>generation_expr</code></em> ) STORED }30 31<span class="phrase">and <em class="replaceable"><code>table_constraint</code></em> is:</span>32 33[ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]34CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ]35 36<span class="phrase">and <em class="replaceable"><code>partition_bound_spec</code></em> is:</span>37 38IN ( <em class="replaceable"><code>partition_bound_expr</code></em> [, ...] ) |39FROM ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] )40  TO ( { <em class="replaceable"><code>partition_bound_expr</code></em> | MINVALUE | MAXVALUE } [, ...] ) |41WITH ( MODULUS <em class="replaceable"><code>numeric_literal</code></em>, REMAINDER <em class="replaceable"><code>numeric_literal</code></em> )42</pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-DESCRIPTION"><h2>Description</h2><p>43   <code class="command">CREATE FOREIGN TABLE</code> creates a new foreign table44   in the current database. The table will be owned by the user issuing the45   command.46  </p><p>47   If a schema name is given (for example, <code class="literal">CREATE FOREIGN TABLE48   myschema.mytable ...</code>) then the table is created in the specified49   schema.  Otherwise it is created in the current schema.50   The name of the foreign table must be51   distinct from the name of any other relation (table, sequence, index, view,52   materialized view, or foreign table) in the same schema.53  </p><p>54   <code class="command">CREATE FOREIGN TABLE</code> also automatically creates a data55   type that represents the composite type corresponding to one row of56   the foreign table.  Therefore, foreign tables cannot have the same57   name as any existing data type in the same schema.58  </p><p>59   If <code class="literal">PARTITION OF</code> clause is specified then the table is60   created as a partition of <code class="literal">parent_table</code> with specified61   bounds.62  </p><p>63   To be able to create a foreign table, you must have <code class="literal">USAGE</code>64   privilege on the foreign server, as well as <code class="literal">USAGE</code>65   privilege on all column types used in the table.66  </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>67      Do not throw an error if a relation with the same name already exists.68      A notice is issued in this case.  Note that there is no guarantee that69      the existing relation is anything like the one that would have been70      created.71     </p></dd><dt><span class="term"><em class="replaceable"><code>table_name</code></em></span></dt><dd><p>72      The name (optionally schema-qualified) of the table to be created.73     </p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>74      The name of a column to be created in the new table.75     </p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p>76      The data type of the column. This can include array77      specifiers. For more information on the data types supported by78      <span class="productname">PostgreSQL</span>, refer to <a class="xref" href="datatype.html" title="Chapter 8. Data Types">Chapter 8</a>.79     </p></dd><dt><span class="term"><code class="literal">COLLATE <em class="replaceable"><code>collation</code></em></code></span></dt><dd><p>80      The <code class="literal">COLLATE</code> clause assigns a collation to81      the column (which must be of a collatable data type).82      If not specified, the column data type's default collation is used.83     </p></dd><dt><span class="term"><code class="literal">INHERITS ( <em class="replaceable"><code>parent_table</code></em> [, ... ] )</code></span></dt><dd><p>84      The optional <code class="literal">INHERITS</code> clause specifies a list of85      tables from which the new foreign table automatically inherits86      all columns.  Parent tables can be plain tables or foreign tables.87      See the similar form of88      <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> for more details.89     </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>90      This form can be used to create the foreign table as partition of91      the given parent table with specified partition bound values.92      See the similar form of93      <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a> for more details.94      Note that it is currently not allowed to create the foreign table as a95      partition of the parent table if there are <code class="literal">UNIQUE</code>96      indexes on the parent table.  (See also97      <a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER TABLE ATTACH PARTITION</code></a>.)98     </p></dd><dt><span class="term"><code class="literal">CONSTRAINT <em class="replaceable"><code>constraint_name</code></em></code></span></dt><dd><p>99      An optional name for a column or table constraint.  If the100      constraint is violated, the constraint name is present in error messages,101      so constraint names like <code class="literal">col must be positive</code> can be used102      to communicate helpful constraint information to client applications.103      (Double-quotes are needed to specify constraint names that contain spaces.)104      If a constraint name is not specified, the system generates a name.105     </p></dd><dt><span class="term"><code class="literal">NOT NULL</code></span></dt><dd><p>106      The column is not allowed to contain null values.107     </p></dd><dt><span class="term"><code class="literal">NULL</code></span></dt><dd><p>108      The column is allowed to contain null values. This is the default.109     </p><p>110      This clause is only provided for compatibility with111      non-standard SQL databases.  Its use is discouraged in new112      applications.113     </p></dd><dt><span class="term"><code class="literal">CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] </code></span></dt><dd><p>114      The <code class="literal">CHECK</code> clause specifies an expression producing a115      Boolean result which each row in the foreign table is expected116      to satisfy; that is, the expression should produce TRUE or UNKNOWN,117      never FALSE, for all rows in the foreign table.118      A check constraint specified as a column constraint should119      reference that column's value only, while an expression120      appearing in a table constraint can reference multiple columns.121     </p><p>122      Currently, <code class="literal">CHECK</code> expressions cannot contain123      subqueries nor refer to variables other than columns of the124      current row.  The system column <code class="literal">tableoid</code>125      may be referenced, but not any other system column.126     </p><p>127      A constraint marked with <code class="literal">NO INHERIT</code> will not propagate to128      child tables.129     </p></dd><dt><span class="term"><code class="literal">DEFAULT130    <em class="replaceable"><code>default_expr</code></em></code></span></dt><dd><p>131      The <code class="literal">DEFAULT</code> clause assigns a default data value for132      the column whose column definition it appears within.  The value133      is any variable-free expression (subqueries and cross-references134      to other columns in the current table are not allowed).  The135      data type of the default expression must match the data type of the136      column.137     </p><p>138      The default expression will be used in any insert operation that139      does not specify a value for the column.  If there is no default140      for a column, then the default is null.141     </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>142      This clause creates the column as a <em class="firstterm">generated143      column</em>.  The column cannot be written to, and when read the144      result of the specified expression will be returned.145     </p><p>146      The keyword <code class="literal">STORED</code> is required to signify that the147      column will be computed on write.  (The computed value will be presented148      to the foreign-data wrapper for storage and must be returned on149      reading.)150     </p><p>151      The generation expression can refer to other columns in the table, but152      not other generated columns.  Any functions and operators used must be153      immutable.  References to other tables are not allowed.154     </p></dd><dt><span class="term"><em class="replaceable"><code>server_name</code></em></span></dt><dd><p>155      The name of an existing foreign server to use for the foreign table.156      For details on defining a server, see <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>.157     </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>158      Options to be associated with the new foreign table or one of its159      columns.160      The allowed option names and values are specific to each foreign161      data wrapper and are validated using the foreign-data wrapper's162      validator function.  Duplicate option names are not allowed (although163      it's OK for a table option and a column option to have the same name).164     </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.66.7"><h2>Notes</h2><p>165    Constraints on foreign tables (such as <code class="literal">CHECK</code>166    or <code class="literal">NOT NULL</code> clauses) are not enforced by the167    core <span class="productname">PostgreSQL</span> system, and most foreign data wrappers168    do not attempt to enforce them either; that is, the constraint is169    simply assumed to hold true.  There would be little point in such170    enforcement since it would only apply to rows inserted or updated via171    the foreign table, and not to rows modified by other means, such as172    directly on the remote server.  Instead, a constraint attached to a173    foreign table should represent a constraint that is being enforced by174    the remote server.175   </p><p>176    Some special-purpose foreign data wrappers might be the only access177    mechanism for the data they access, and in that case it might be178    appropriate for the foreign data wrapper itself to perform constraint179    enforcement.  But you should not assume that a wrapper does that180    unless its documentation says so.181   </p><p>182    Although <span class="productname">PostgreSQL</span> does not attempt to enforce183    constraints on foreign tables, it does assume that they are correct184    for purposes of query optimization.  If there are rows visible in the185    foreign table that do not satisfy a declared constraint, queries on186    the table might produce errors or incorrect answers.  It is the user's187    responsibility to ensure that the constraint definition matches188    reality.189   </p><div class="caution"><h3 class="title">Caution</h3><p>190     When a foreign table is used as a partition of a partitioned table,191     there is an implicit constraint that its contents must satisfy the192     partitioning rule.  Again, it is the user's responsibility to ensure193     that that is true, which is best done by installing a matching194     constraint on the remote server.195    </p></div><p>196    Within a partitioned table containing foreign-table partitions,197    an <code class="command">UPDATE</code> that changes the partition key value can198    cause a row to be moved from a local partition to a foreign-table199    partition, provided the foreign data wrapper supports tuple routing.200    However, it is not currently possible to move a row from a201    foreign-table partition to another partition.202    An <code class="command">UPDATE</code> that would require doing that will fail203    due to the partitioning constraint, assuming that that is properly204    enforced by the remote server.205   </p><p>206    Similar considerations apply to generated columns.  Stored generated207    columns are computed on insert or update on the local208    <span class="productname">PostgreSQL</span> server and handed to the209    foreign-data wrapper for writing out to the foreign data store, but it is210    not enforced that a query of the foreign table returns values for stored211    generated columns that are consistent with the generation expression.212    Again, this might result in incorrect query results.213   </p></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-EXAMPLES"><h2>Examples</h2><p>214   Create foreign table <code class="structname">films</code>, which will be accessed through215   the server <code class="structname">film_server</code>:216 217</p><pre class="programlisting">218CREATE FOREIGN TABLE films (219    code        char(5) NOT NULL,220    title       varchar(40) NOT NULL,221    did         integer NOT NULL,222    date_prod   date,223    kind        varchar(10),224    len         interval hour to minute225)226SERVER film_server;227</pre><p>228   Create foreign table <code class="structname">measurement_y2016m07</code>, which will be229   accessed through the server <code class="structname">server_07</code>, as a partition230   of the range partitioned table <code class="structname">measurement</code>:231 232</p><pre class="programlisting">233CREATE FOREIGN TABLE measurement_y2016m07234    PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')235    SERVER server_07;236</pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-COMPATIBILITY"><h2>Compatibility</h2><p>237   The <code class="command">CREATE FOREIGN TABLE</code> command largely conforms to the238   <acronym class="acronym">SQL</acronym> standard; however, much as with239   <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>,240   <code class="literal">NULL</code> constraints and zero-column foreign tables are permitted.241   The ability to specify column default values is also242   a <span class="productname">PostgreSQL</span> extension.  Table inheritance, in the form243   defined by <span class="productname">PostgreSQL</span>, is nonstandard.244  </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>
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