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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 V1.79.1" /><link rel="prev" href="sql-createforeigndatawrapper.html" title="CREATE FOREIGN DATA WRAPPER" /><link rel="next" href="sql-createfunction.html" title="CREATE FUNCTION" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" 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 12.4 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></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">

  3. CREATE 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. 

  12. CREATE 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. ) ] <em class="replaceable"><code>partition_bound_spec</code></em>

  18.   SERVER <em class="replaceable"><code>server_name</code></em>

  19. [ OPTIONS ( <em class="replaceable"><code>option</code></em> '<em class="replaceable"><code>value</code></em>' [, ... ] ) ]

  20. 

  21. <span class="phrase">where <em class="replaceable"><code>column_constraint</code></em> is:</span>

  22. 

  23. [ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]

  24. { NOT NULL |

  25.   NULL |

  26.   CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] |

  27.   DEFAULT <em class="replaceable"><code>default_expr</code></em> |

  28.   GENERATED ALWAYS AS ( <em class="replaceable"><code>generation_expr</code></em> ) STORED }

  29. 

  30. <span class="phrase">and <em class="replaceable"><code>table_constraint</code></em> is:</span>

  31. 

  32. [ CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ]

  33. CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ]

  34. </pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-DESCRIPTION"><h2>Description</h2><p>

  35.    <code class="command">CREATE FOREIGN TABLE</code> creates a new foreign table

  36.    in the current database. The table will be owned by the user issuing the

  37.    command.

  38.   </p><p>

  39.    If a schema name is given (for example, <code class="literal">CREATE FOREIGN TABLE

  40.    myschema.mytable ...</code>) then the table is created in the specified

  41.    schema.  Otherwise it is created in the current schema.

  42.    The name of the foreign table must be

  43.    distinct from the name of any other foreign table, table, sequence, index,

  44.    view, or materialized view in the same schema.

  45.   </p><p>

  46.    <code class="command">CREATE FOREIGN TABLE</code> also automatically creates a data

  47.    type that represents the composite type corresponding to one row of

  48.    the foreign table.  Therefore, foreign tables cannot have the same

  49.    name as any existing data type in the same schema.

  50.   </p><p>

  51.    If <code class="literal">PARTITION OF</code> clause is specified then the table is

  52.    created as a partition of <code class="literal">parent_table</code> with specified

  53.    bounds.

  54.   </p><p>

  55.    To be able to create a foreign table, you must have <code class="literal">USAGE</code>

  56.    privilege on the foreign server, as well as <code class="literal">USAGE</code>

  57.    privilege on all column types used in the table.

  58.   </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>

  59.       Do not throw an error if a relation with the same name already exists.

  60.       A notice is issued in this case.  Note that there is no guarantee that

  61.       the existing relation is anything like the one that would have been

  62.       created.

  63.      </p></dd><dt><span class="term"><em class="replaceable"><code>table_name</code></em></span></dt><dd><p>

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

  65.      </p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>

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

  67.      </p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p>

  68.       The data type of the column. This can include array

  69.       specifiers. For more information on the data types supported by

  70.       <span class="productname">PostgreSQL</span>, refer to <a class="xref" href="datatype.html" title="Chapter 8. Data Types">Chapter 8</a>.

  71.      </p></dd><dt><span class="term"><code class="literal">COLLATE <em class="replaceable"><code>collation</code></em></code></span></dt><dd><p>

  72.       The <code class="literal">COLLATE</code> clause assigns a collation to

  73.       the column (which must be of a collatable data type).

  74.       If not specified, the column data type's default collation is used.

  75.      </p></dd><dt><span class="term"><code class="literal">INHERITS ( <em class="replaceable"><code>parent_table</code></em> [, ... ] )</code></span></dt><dd><p>

  76.       The optional <code class="literal">INHERITS</code> clause specifies a list of

  77.       tables from which the new foreign table automatically inherits

  78.       all columns.  Parent tables can be plain tables or foreign tables.

  79.       See the similar form of

  80.       <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a> for more details.

  81.      </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></code></span></dt><dd><p>

  82.       This form can be used to create the foreign table as partition of

  83.       the given parent table with specified partition bound values.

  84.       See the similar form of

  85.       <a class="xref" href="sql-createtable.html" title="CREATE TABLE"><span class="refentrytitle">CREATE TABLE</span></a> for more details.

  86.       Note that it is currently not allowed to create the foreign table as a

  87.       partition of the parent table if there are <code class="literal">UNIQUE</code>

  88.       indexes on the parent table.  (See also

  89.       <a class="link" href="sql-altertable.html" title="ALTER TABLE"><code class="command">ALTER TABLE ATTACH PARTITION</code></a>.)

  90.      </p></dd><dt><span class="term"><code class="literal">CONSTRAINT <em class="replaceable"><code>constraint_name</code></em></code></span></dt><dd><p>

  91.       An optional name for a column or table constraint.  If the

  92.       constraint is violated, the constraint name is present in error messages,

  93.       so constraint names like <code class="literal">col must be positive</code> can be used

  94.       to communicate helpful constraint information to client applications.

  95.       (Double-quotes are needed to specify constraint names that contain spaces.)

  96.       If a constraint name is not specified, the system generates a name.

  97.      </p></dd><dt><span class="term"><code class="literal">NOT NULL</code></span></dt><dd><p>

  98.       The column is not allowed to contain null values.

  99.      </p></dd><dt><span class="term"><code class="literal">NULL</code></span></dt><dd><p>

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

  101.      </p><p>

  102.       This clause is only provided for compatibility with

  103.       non-standard SQL databases.  Its use is discouraged in new

  104.       applications.

  105.      </p></dd><dt><span class="term"><code class="literal">CHECK ( <em class="replaceable"><code>expression</code></em> ) [ NO INHERIT ] </code></span></dt><dd><p>

  106.       The <code class="literal">CHECK</code> clause specifies an expression producing a

  107.       Boolean result which each row in the foreign table is expected

  108.       to satisfy; that is, the expression should produce TRUE or UNKNOWN,

  109.       never FALSE, for all rows in the foreign table.

  110.       A check constraint specified as a column constraint should

  111.       reference that column's value only, while an expression

  112.       appearing in a table constraint can reference multiple columns.

  113.      </p><p>

  114.       Currently, <code class="literal">CHECK</code> expressions cannot contain

  115.       subqueries nor refer to variables other than columns of the

  116.       current row.  The system column <code class="literal">tableoid</code>

  117.       may be referenced, but not any other system column.

  118.      </p><p>

  119.       A constraint marked with <code class="literal">NO INHERIT</code> will not propagate to

  120.       child tables.

  121.      </p></dd><dt><span class="term"><code class="literal">DEFAULT

  122.     <em class="replaceable"><code>default_expr</code></em></code></span></dt><dd><p>

  123.       The <code class="literal">DEFAULT</code> clause assigns a default data value for

  124.       the column whose column definition it appears within.  The value

  125.       is any variable-free expression (subqueries and cross-references

  126.       to other columns in the current table are not allowed).  The

  127.       data type of the default expression must match the data type of the

  128.       column.

  129.      </p><p>

  130.       The default expression will be used in any insert operation that

  131.       does not specify a value for the column.  If there is no default

  132.       for a column, then the default is null.

  133.      </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>

  134.       This clause creates the column as a <em class="firstterm">generated

  135.       column</em>.  The column cannot be written to, and when read the

  136.       result of the specified expression will be returned.

  137.      </p><p>

  138.       The keyword <code class="literal">STORED</code> is required to signify that the

  139.       column will be computed on write.  (The computed value will be presented

  140.       to the foreign-data wrapper for storage and must be returned on

  141.       reading.)

  142.      </p><p>

  143.       The generation expression can refer to other columns in the table, but

  144.       not other generated columns.  Any functions and operators used must be

  145.       immutable.  References to other tables are not allowed.

  146.      </p></dd><dt><span class="term"><em class="replaceable"><code>server_name</code></em></span></dt><dd><p>

  147.       The name of an existing foreign server to use for the foreign table.

  148.       For details on defining a server, see <a class="xref" href="sql-createserver.html" title="CREATE SERVER"><span class="refentrytitle">CREATE SERVER</span></a>.

  149.      </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>

  150.       Options to be associated with the new foreign table or one of its

  151.       columns.

  152.       The allowed option names and values are specific to each foreign

  153.       data wrapper and are validated using the foreign-data wrapper's

  154.       validator function.  Duplicate option names are not allowed (although

  155.       it's OK for a table option and a column option to have the same name).

  156.      </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.66.7"><h2>Notes</h2><p>

  157.     Constraints on foreign tables (such as <code class="literal">CHECK</code>

  158.     or <code class="literal">NOT NULL</code> clauses) are not enforced by the

  159.     core <span class="productname">PostgreSQL</span> system, and most foreign data wrappers

  160.     do not attempt to enforce them either; that is, the constraint is

  161.     simply assumed to hold true.  There would be little point in such

  162.     enforcement since it would only apply to rows inserted or updated via

  163.     the foreign table, and not to rows modified by other means, such as

  164.     directly on the remote server.  Instead, a constraint attached to a

  165.     foreign table should represent a constraint that is being enforced by

  166.     the remote server.

  167.    </p><p>

  168.     Some special-purpose foreign data wrappers might be the only access

  169.     mechanism for the data they access, and in that case it might be

  170.     appropriate for the foreign data wrapper itself to perform constraint

  171.     enforcement.  But you should not assume that a wrapper does that

  172.     unless its documentation says so.

  173.    </p><p>

  174.     Although <span class="productname">PostgreSQL</span> does not attempt to enforce

  175.     constraints on foreign tables, it does assume that they are correct

  176.     for purposes of query optimization.  If there are rows visible in the

  177.     foreign table that do not satisfy a declared constraint, queries on

  178.     the table might produce incorrect answers.  It is the user's

  179.     responsibility to ensure that the constraint definition matches

  180.     reality.

  181.    </p><p>

  182.     Similar considerations apply to generated columns.  Stored generated

  183.     columns are computed on insert or update on the local

  184.     <span class="productname">PostgreSQL</span> server and handed to the

  185.     foreign-data wrapper for writing out to the foreign data store, but it is

  186.     not enforced that a query of the foreign table returns values for stored

  187.     generated columns that are consistent with the generation expression.

  188.     Again, this might result in incorrect query results.

  189.    </p><p>

  190.     While rows can be moved from local partitions to a foreign-table partition

  191.     (provided the foreign data wrapper supports tuple routing), they cannot be

  192.     moved from a foreign-table partition to another partition.

  193.    </p></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-EXAMPLES"><h2>Examples</h2><p>

  194.    Create foreign table <code class="structname">films</code>, which will be accessed through

  195.    the server <code class="structname">film_server</code>:

  196. 

  197. </p><pre class="programlisting">

  198. CREATE FOREIGN TABLE films (

  199.     code        char(5) NOT NULL,

  200.     title       varchar(40) NOT NULL,

  201.     did         integer NOT NULL,

  202.     date_prod   date,

  203.     kind        varchar(10),

  204.     len         interval hour to minute

  205. )

  206. SERVER film_server;

  207. </pre><p>

  208.    Create foreign table <code class="structname">measurement_y2016m07</code>, which will be

  209.    accessed through the server <code class="structname">server_07</code>, as a partition

  210.    of the range partitioned table <code class="structname">measurement</code>:

  211. 

  212. </p><pre class="programlisting">

  213. CREATE FOREIGN TABLE measurement_y2016m07

  214.     PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')

  215.     SERVER server_07;

  216. </pre></div><div class="refsect1" id="SQL-CREATEFOREIGNTABLE-COMPATIBILITY"><h2>Compatibility</h2><p>

  217.    The <code class="command">CREATE FOREIGN TABLE</code> command largely conforms to the

  218.    <acronym class="acronym">SQL</acronym> standard; however, much as with

  219.    <a class="link" href="sql-createtable.html" title="CREATE TABLE"><code class="command">CREATE TABLE</code></a>,

  220.    <code class="literal">NULL</code> constraints and zero-column foreign tables are permitted.

  221.    The ability to specify column default values is also

  222.    a <span class="productname">PostgreSQL</span> extension.  Table inheritance, in the form

  223.    defined by <span class="productname">PostgreSQL</span>, is nonstandard.

  224.   </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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createfunction.html">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">Home</a></td><td width="40%" align="right" valign="top"> CREATE FUNCTION</td></tr></table></div></body></html>
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