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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>