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When a partitioned tables contains foreign tables as partitions, it is not possible to implement unique or primary key indexes -- but when regular indexes are created, there is no reason to do anything other than ignoring such partitions. We were raising errors upon encountering the foreign partitions, which is unfriendly and doesn't protect against any actual problems. Relax this restriction so that index creation is allowed on partitioned tables containing foreign partitions, becoming a no-op on them. (We may later want to redefine this so that the FDW is told to create the indexes on the foreign side.) This applies to CREATE INDEX, as well as ALTER TABLE / ATTACH PARTITION and CREATE TABLE / PARTITION OF. Backpatch to 11, where indexes on partitioned tables were introduced. Discussion: https://postgr.es/m/15724-d5a58fa9472eef4f@postgresql.org Author: Álvaro Herrera Reviewed-by: Amit Langote
394 lines
14 KiB
Plaintext
394 lines
14 KiB
Plaintext
<!-- doc/src/sgml/ref/create_foreign_table.sgml -->
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<refentry id="sql-createforeigntable">
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<indexterm zone="sql-createforeigntable">
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<primary>CREATE FOREIGN TABLE</primary>
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</indexterm>
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<refmeta>
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<refentrytitle>CREATE FOREIGN TABLE</refentrytitle>
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<manvolnum>7</manvolnum>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>CREATE FOREIGN TABLE</refname>
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<refpurpose>define a new foreign table</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<synopsis>
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CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable> ( [
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{ <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ OPTIONS ( <replaceable class="parameter">option</replaceable> '<replaceable class="parameter">value</replaceable>' [, ... ] ) ] [ COLLATE <replaceable>collation</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
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| <replaceable>table_constraint</replaceable> }
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[, ... ]
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] )
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[ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
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SERVER <replaceable class="parameter">server_name</replaceable>
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[ OPTIONS ( <replaceable class="parameter">option</replaceable> '<replaceable class="parameter">value</replaceable>' [, ... ] ) ]
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CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable>
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PARTITION OF <replaceable class="parameter">parent_table</replaceable> [ (
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{ <replaceable class="parameter">column_name</replaceable> [ WITH OPTIONS ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
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| <replaceable>table_constraint</replaceable> }
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[, ... ]
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) ] <replaceable class="parameter">partition_bound_spec</replaceable>
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SERVER <replaceable class="parameter">server_name</replaceable>
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[ OPTIONS ( <replaceable class="parameter">option</replaceable> '<replaceable class="parameter">value</replaceable>' [, ... ] ) ]
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<phrase>where <replaceable class="parameter">column_constraint</replaceable> is:</phrase>
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[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
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{ NOT NULL |
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NULL |
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CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
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DEFAULT <replaceable>default_expr</replaceable> }
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<phrase>and <replaceable class="parameter">table_constraint</replaceable> is:</phrase>
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[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
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CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ]
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</synopsis>
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</refsynopsisdiv>
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<refsect1 id="sql-createforeigntable-description">
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<title>Description</title>
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<para>
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<command>CREATE FOREIGN TABLE</command> creates a new foreign table
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in the current database. The table will be owned by the user issuing the
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command.
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</para>
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<para>
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If a schema name is given (for example, <literal>CREATE FOREIGN TABLE
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myschema.mytable ...</literal>) then the table is created in the specified
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schema. Otherwise it is created in the current schema.
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The name of the foreign table must be
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distinct from the name of any other foreign table, table, sequence, index,
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view, or materialized view in the same schema.
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</para>
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<para>
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<command>CREATE FOREIGN TABLE</command> also automatically creates a data
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type that represents the composite type corresponding to one row of
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the foreign table. Therefore, foreign tables cannot have the same
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name as any existing data type in the same schema.
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</para>
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<para>
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If <literal>PARTITION OF</literal> clause is specified then the table is
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created as a partition of <literal>parent_table</literal> with specified
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bounds.
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</para>
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<para>
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To be able to create a foreign table, you must have <literal>USAGE</literal>
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privilege on the foreign server, as well as <literal>USAGE</literal>
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privilege on all column types used in the table.
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</para>
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</refsect1>
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<refsect1>
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<title>Parameters</title>
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<variablelist>
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<varlistentry>
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<term><literal>IF NOT EXISTS</literal></term>
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<listitem>
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<para>
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Do not throw an error if a relation with the same name already exists.
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A notice is issued in this case. Note that there is no guarantee that
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the existing relation is anything like the one that would have been
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created.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">table_name</replaceable></term>
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<listitem>
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<para>
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The name (optionally schema-qualified) of the table to be created.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">column_name</replaceable></term>
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<listitem>
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<para>
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The name of a column to be created in the new table.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">data_type</replaceable></term>
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<listitem>
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<para>
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The data type of the column. This can include array
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specifiers. For more information on the data types supported by
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<productname>PostgreSQL</productname>, refer to <xref
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linkend="datatype"/>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>COLLATE <replaceable>collation</replaceable></literal></term>
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<listitem>
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<para>
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The <literal>COLLATE</literal> clause assigns a collation to
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the column (which must be of a collatable data type).
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If not specified, the column data type's default collation is used.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term>
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<listitem>
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<para>
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The optional <literal>INHERITS</literal> clause specifies a list of
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tables from which the new foreign table automatically inherits
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all columns. Parent tables can be plain tables or foreign tables.
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See the similar form of
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<xref linkend="sql-createtable"/> for more details.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>PARTITION OF <replaceable>parent_table</replaceable> FOR VALUES <replaceable class="parameter">partition_bound_spec</replaceable></literal></term>
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<listitem>
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<para>
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This form can be used to create the foreign table as partition of
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the given parent table with specified partition bound values.
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See the similar form of
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<xref linkend="sql-createtable"/> for more details.
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Note that it is currently not allowed to create the foreign table as a
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partition of the parent table if there are <literal>UNIQUE</literal>
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indexes on the parent table. (See also
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<link linkend="sql-altertable"><command>ALTER TABLE ATTACH PARTITION</command></link>.)
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>CONSTRAINT <replaceable class="parameter">constraint_name</replaceable></literal></term>
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<listitem>
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<para>
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An optional name for a column or table constraint. If the
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constraint is violated, the constraint name is present in error messages,
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so constraint names like <literal>col must be positive</literal> can be used
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to communicate helpful constraint information to client applications.
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(Double-quotes are needed to specify constraint names that contain spaces.)
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If a constraint name is not specified, the system generates a name.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>NOT NULL</literal></term>
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<listitem>
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<para>
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The column is not allowed to contain null values.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>NULL</literal></term>
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<listitem>
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<para>
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The column is allowed to contain null values. This is the default.
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</para>
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<para>
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This clause is only provided for compatibility with
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non-standard SQL databases. Its use is discouraged in new
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applications.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] </literal></term>
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<listitem>
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<para>
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The <literal>CHECK</literal> clause specifies an expression producing a
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Boolean result which each row in the foreign table is expected
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to satisfy; that is, the expression should produce TRUE or UNKNOWN,
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never FALSE, for all rows in the foreign table.
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A check constraint specified as a column constraint should
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reference that column's value only, while an expression
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appearing in a table constraint can reference multiple columns.
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</para>
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<para>
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Currently, <literal>CHECK</literal> expressions cannot contain
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subqueries nor refer to variables other than columns of the
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current row. The system column <literal>tableoid</literal>
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may be referenced, but not any other system column.
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</para>
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<para>
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A constraint marked with <literal>NO INHERIT</literal> will not propagate to
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child tables.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>DEFAULT
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<replaceable>default_expr</replaceable></literal></term>
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<listitem>
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<para>
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The <literal>DEFAULT</literal> clause assigns a default data value for
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the column whose column definition it appears within. The value
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is any variable-free expression (subqueries and cross-references
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to other columns in the current table are not allowed). The
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data type of the default expression must match the data type of the
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column.
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</para>
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<para>
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The default expression will be used in any insert operation that
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does not specify a value for the column. If there is no default
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for a column, then the default is null.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">server_name</replaceable></term>
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<listitem>
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<para>
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The name of an existing foreign server to use for the foreign table.
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For details on defining a server, see <xref
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linkend="sql-createserver"/>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>OPTIONS ( <replaceable class="parameter">option</replaceable> '<replaceable class="parameter">value</replaceable>' [, ...] )</literal></term>
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<listitem>
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<para>
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Options to be associated with the new foreign table or one of its
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columns.
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The allowed option names and values are specific to each foreign
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data wrapper and are validated using the foreign-data wrapper's
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validator function. Duplicate option names are not allowed (although
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it's OK for a table option and a column option to have the same name).
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Constraints on foreign tables (such as <literal>CHECK</literal>
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or <literal>NOT NULL</literal> clauses) are not enforced by the
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core <productname>PostgreSQL</productname> system, and most foreign data wrappers
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do not attempt to enforce them either; that is, the constraint is
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simply assumed to hold true. There would be little point in such
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enforcement since it would only apply to rows inserted or updated via
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the foreign table, and not to rows modified by other means, such as
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directly on the remote server. Instead, a constraint attached to a
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foreign table should represent a constraint that is being enforced by
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the remote server.
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</para>
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<para>
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Some special-purpose foreign data wrappers might be the only access
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mechanism for the data they access, and in that case it might be
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appropriate for the foreign data wrapper itself to perform constraint
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enforcement. But you should not assume that a wrapper does that
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unless its documentation says so.
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</para>
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<para>
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Although <productname>PostgreSQL</productname> does not attempt to enforce
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constraints on foreign tables, it does assume that they are correct
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for purposes of query optimization. If there are rows visible in the
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foreign table that do not satisfy a declared constraint, queries on
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the table might produce incorrect answers. It is the user's
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responsibility to ensure that the constraint definition matches
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reality.
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</para>
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<para>
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While rows can be moved from local partitions to a foreign-table partition
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(provided the foreign data wrapper supports tuple routing), they cannot be
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moved from a foreign-table partition to another partition.
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</para>
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</refsect1>
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<refsect1 id="sql-createforeigntable-examples">
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<title>Examples</title>
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<para>
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Create foreign table <structname>films</structname>, which will be accessed through
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the server <structname>film_server</structname>:
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<programlisting>
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CREATE FOREIGN TABLE films (
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code char(5) NOT NULL,
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title varchar(40) NOT NULL,
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did integer NOT NULL,
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date_prod date,
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kind varchar(10),
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len interval hour to minute
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)
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SERVER film_server;
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</programlisting></para>
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<para>
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Create foreign table <structname>measurement_y2016m07</structname>, which will be
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accessed through the server <structname>server_07</structname>, as a partition
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of the range partitioned table <structname>measurement</structname>:
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<programlisting>
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CREATE FOREIGN TABLE measurement_y2016m07
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PARTITION OF measurement FOR VALUES FROM ('2016-07-01') TO ('2016-08-01')
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SERVER server_07;
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</programlisting></para>
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</refsect1>
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<refsect1 id="sql-createforeigntable-compatibility">
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<title id="sql-createforeigntable-compatibility-title">Compatibility</title>
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<para>
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The <command>CREATE FOREIGN TABLE</command> command largely conforms to the
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<acronym>SQL</acronym> standard; however, much as with
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<link linkend="sql-createtable"><command>CREATE TABLE</command></link>,
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<literal>NULL</literal> constraints and zero-column foreign tables are permitted.
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The ability to specify column default values is also
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a <productname>PostgreSQL</productname> extension. Table inheritance, in the form
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defined by <productname>PostgreSQL</productname>, is nonstandard.
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</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<simplelist type="inline">
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<member><xref linkend="sql-alterforeigntable"/></member>
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<member><xref linkend="sql-dropforeigntable"/></member>
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<member><xref linkend="sql-createtable"/></member>
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<member><xref linkend="sql-createserver"/></member>
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<member><xref linkend="sql-importforeignschema"/></member>
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</simplelist>
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</refsect1>
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</refentry>
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