<!--
doc/src/sgml/rel/alter_foreign_table.sgml
PostgreSQL documentation
-->

<refentry id="sql-alterforeigntable">
 <indexterm zone="sql-alterforeigntable">
  <primary>ALTER FOREIGN TABLE</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>ALTER FOREIGN TABLE</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>ALTER FOREIGN TABLE</refname>
  <refpurpose>change the definition of a foreign table</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
ALTER FOREIGN TABLE [ IF EXISTS ] [ ONLY ] <replaceable class="parameter">name</replaceable> [ * ]
    <replaceable class="parameter">action</replaceable> [, ... ]
ALTER FOREIGN TABLE [ IF EXISTS ] [ ONLY ] <replaceable class="parameter">name</replaceable> [ * ]
    RENAME [ COLUMN ] <replaceable class="parameter">column_name</replaceable> TO <replaceable class="parameter">new_column_name</replaceable>
ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
    RENAME TO <replaceable class="parameter">new_name</replaceable>
ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
    SET SCHEMA <replaceable class="parameter">new_schema</replaceable>

<phrase>where <replaceable class="parameter">action</replaceable> is one of:</phrase>

    ADD [ COLUMN ] [ IF NOT EXISTS ] <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
    DROP [ COLUMN ] [ IF EXISTS ] <replaceable class="parameter">column_name</replaceable> [ RESTRICT | CASCADE ]
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> [ SET DATA ] TYPE <replaceable class="parameter">data_type</replaceable> [ COLLATE <replaceable class="parameter">collation</replaceable> ]
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET DEFAULT <replaceable class="parameter">expression</replaceable>
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP DEFAULT
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET | DROP } NOT NULL
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STATISTICS <replaceable class="parameter">integer</replaceable>
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> OPTIONS ( [ ADD | SET | DROP ] <replaceable class="parameter">option</replaceable> ['<replaceable class="parameter">value</replaceable>'] [, ... ])
    ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]
    VALIDATE CONSTRAINT <replaceable class="parameter">constraint_name</replaceable>
    DROP CONSTRAINT [ IF EXISTS ]  <replaceable class="parameter">constraint_name</replaceable> [ RESTRICT | CASCADE ]
    DISABLE TRIGGER [ <replaceable class="parameter">trigger_name</replaceable> | ALL | USER ]
    ENABLE TRIGGER [ <replaceable class="parameter">trigger_name</replaceable> | ALL | USER ]
    ENABLE REPLICA TRIGGER <replaceable class="parameter">trigger_name</replaceable>
    ENABLE ALWAYS TRIGGER <replaceable class="parameter">trigger_name</replaceable>
    SET WITHOUT OIDS
    INHERIT <replaceable class="parameter">parent_table</replaceable>
    NO INHERIT <replaceable class="parameter">parent_table</replaceable>
    OWNER TO { <replaceable class="parameter">new_owner</replaceable> | CURRENT_ROLE | CURRENT_USER | SESSION_USER }
    OPTIONS ( [ ADD | SET | DROP ] <replaceable class="parameter">option</replaceable> ['<replaceable class="parameter">value</replaceable>'] [, ... ])
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>ALTER FOREIGN TABLE</command> changes the definition of an
   existing foreign table.  There are several subforms:

  <variablelist>
   <varlistentry>
    <term><literal>ADD [ COLUMN ] [ IF NOT EXISTS ]</literal></term>
    <listitem>
     <para>
      This form adds a new column to the foreign table, using the same syntax as
      <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.
      If <literal>IF NOT EXISTS</literal> is specified and a column already
      exists with this name, no error is thrown.
      Unlike the case when adding a column to a regular table, nothing happens
      to the underlying storage: this action simply declares that
      some new column is now accessible through the foreign table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DROP [ COLUMN ] [ IF EXISTS ]</literal></term>
    <listitem>
     <para>
      This form drops a column from a foreign table.
      You will need to say <literal>CASCADE</literal> if
      anything outside the table depends on the column; for example,
      views.
      If <literal>IF EXISTS</literal> is specified and the column
      does not exist, no error is thrown. In this case a notice
      is issued instead.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET DATA TYPE</literal></term>
    <listitem>
     <para>
      This form changes the type of a column of a foreign table.
      Again, this has no effect on any underlying storage: this action simply
      changes the type that <productname>PostgreSQL</productname> believes the column to
      have.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET</literal>/<literal>DROP DEFAULT</literal></term>
    <listitem>
     <para>
      These forms set or remove the default value for a column.
      Default values only apply in subsequent <command>INSERT</command>
      or <command>UPDATE</command> commands; they do not cause rows already in the
      table to change.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET</literal>/<literal>DROP NOT NULL</literal></term>
    <listitem>
     <para>
      Mark a column as allowing, or not allowing, null values.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET STATISTICS</literal></term>
    <listitem>
     <para>
      This form
      sets the per-column statistics-gathering target for subsequent
      <link linkend="sql-analyze"><command>ANALYZE</command></link> operations.
      See the similar form of <link linkend="sql-altertable"><command>ALTER TABLE</command></link>
      for more details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )</literal></term>
    <term><literal>RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )</literal></term>
    <listitem>
     <para>
      This form sets or resets per-attribute options.
      See the similar form of <link linkend="sql-altertable"><command>ALTER TABLE</command></link>
      for more details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term>
     <literal>SET STORAGE</literal>
    </term>
    <listitem>
     <para>
      This form sets the storage mode for a column.
      See the similar form of <link linkend="sql-altertable"><command>ALTER TABLE</command></link>
      for more details.
      Note that the storage mode has no effect unless the table's
      foreign-data wrapper chooses to pay attention to it.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]</literal></term>
    <listitem>
     <para>
      This form adds a new constraint to a foreign table, using the same
      syntax as <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.
      Currently only <literal>CHECK</literal> and <literal>NOT NULL</literal>
      constraints are supported.
     </para>

     <para>
      Unlike the case when adding a constraint to a regular table, nothing is
      done to verify the constraint is correct; rather, this action simply
      declares that some new condition should be assumed to hold for all rows
      in the foreign table.  (See the discussion
      in <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.)
      If the constraint is marked <literal>NOT VALID</literal> (allowed only for
      the <literal>CHECK</literal> case), then it isn't
      assumed to hold, but is only recorded for possible future use.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>VALIDATE CONSTRAINT</literal></term>
    <listitem>
     <para>
      This form marks as valid a constraint that was previously marked
      as <literal>NOT VALID</literal>.  No action is taken to verify the
      constraint, but future queries will assume that it holds.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DROP CONSTRAINT [ IF EXISTS ]</literal></term>
    <listitem>
     <para>
      This form drops the specified constraint on a foreign table.
      If <literal>IF EXISTS</literal> is specified and the constraint
      does not exist, no error is thrown.
      In this case a notice is issued instead.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>DISABLE</literal>/<literal>ENABLE [ REPLICA | ALWAYS ] TRIGGER</literal></term>
    <listitem>
     <para>
      These forms configure the firing of trigger(s) belonging to the foreign
      table.  See the similar form of <link linkend="sql-altertable"><command>ALTER TABLE</command></link> for more
      details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET WITHOUT OIDS</literal></term>
    <listitem>
     <para>
      Backward compatibility syntax for removing the <literal>oid</literal>
      system column. As <literal>oid</literal> system columns cannot be added
      anymore, this never has an effect.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>INHERIT <replaceable class="parameter">parent_table</replaceable></literal></term>
    <listitem>
     <para>
      This form adds the target foreign table as a new child of the specified
      parent table.
      See the similar form of <link linkend="sql-altertable"><command>ALTER TABLE</command></link>
      for more details.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>NO INHERIT <replaceable class="parameter">parent_table</replaceable></literal></term>
    <listitem>
     <para>
      This form removes the target foreign table from the list of children of
      the specified parent table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OWNER</literal></term>
    <listitem>
     <para>
      This form changes the owner of the foreign table to the
      specified user.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>OPTIONS ( [ ADD | SET | DROP ] <replaceable class="parameter">option</replaceable> ['<replaceable class="parameter">value</replaceable>'] [, ... ] )</literal></term>
    <listitem>
     <para>
      Change options for the foreign table or one of its columns.
      <literal>ADD</literal>, <literal>SET</literal>, and <literal>DROP</literal>
      specify the action to be performed.  <literal>ADD</literal> is assumed
      if no operation is explicitly specified.  Duplicate option names are not
      allowed (although it's OK for a table option and a column option to have
      the same name).  Option names and values are also validated using the
      foreign data wrapper library.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>RENAME</literal></term>
    <listitem>
     <para>
      The <literal>RENAME</literal> forms change the name of a foreign table
      or the name of an individual column in a foreign table.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>SET SCHEMA</literal></term>
    <listitem>
     <para>
      This form moves the foreign table into another schema.
     </para>
    </listitem>
   </varlistentry>

  </variablelist>
  </para>

  <para>
   All the actions except <literal>RENAME</literal> and <literal>SET SCHEMA</literal>
   can be combined into
   a list of multiple alterations to apply in parallel.  For example, it
   is possible to add several columns and/or alter the type of several
   columns in a single command.
  </para>

  <para>
   If the command is written as <literal>ALTER FOREIGN TABLE IF EXISTS ...</literal>
   and the foreign table does not exist, no error is thrown. A notice is
   issued in this case.
  </para>

  <para>
   You must own the table to use <command>ALTER FOREIGN TABLE</command>.
   To change the schema of a foreign table, you must also have
   <literal>CREATE</literal> privilege on the new schema.
   To alter the owner, you must be able to <literal>SET ROLE</literal> to the
   new owning role, and that role must have <literal>CREATE</literal> privilege
   on the table's schema.  (These restrictions enforce that altering the owner
   doesn't do anything you couldn't do by dropping and recreating the table.
   However, a superuser can alter ownership of any table anyway.)
   To add a column or alter a column type, you must also
   have <literal>USAGE</literal> privilege on the data type.
  </para>
 </refsect1>

 <refsect1>
  <title>Parameters</title>

    <variablelist>

     <varlistentry>
      <term><replaceable class="parameter">name</replaceable></term>
      <listitem>
       <para>
        The name (possibly schema-qualified) of an existing foreign table to
        alter. If <literal>ONLY</literal> is specified before the table name, only
        that table is altered. If <literal>ONLY</literal> is not specified, the table
        and all its descendant tables (if any) are altered.  Optionally,
        <literal>*</literal> can be specified after the table name to explicitly
        indicate that descendant tables are included.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">column_name</replaceable></term>
      <listitem>
       <para>
        Name of a new or existing column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_column_name</replaceable></term>
      <listitem>
       <para>
        New name for an existing column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_name</replaceable></term>
      <listitem>
       <para>
        New name for the table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">data_type</replaceable></term>
      <listitem>
       <para>
        Data type of the new column, or new data type for an existing
        column.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">table_constraint</replaceable></term>
      <listitem>
       <para>
        New table constraint for the foreign table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">constraint_name</replaceable></term>
      <listitem>
       <para>
        Name of an existing constraint to drop.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>CASCADE</literal></term>
      <listitem>
       <para>
        Automatically drop objects that depend on the dropped column
        or constraint (for example, views referencing the column),
        and in turn all objects that depend on those objects
        (see <xref linkend="ddl-depend"/>).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>RESTRICT</literal></term>
      <listitem>
       <para>
        Refuse to drop the column or constraint if there are any dependent
        objects. This is the default behavior.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">trigger_name</replaceable></term>
      <listitem>
       <para>
        Name of a single trigger to disable or enable.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>ALL</literal></term>
      <listitem>
       <para>
        Disable or enable all triggers belonging to the foreign table.  (This
        requires superuser privilege if any of the triggers are internally
        generated triggers.  The core system does not add such triggers to
        foreign tables, but add-on code could do so.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>USER</literal></term>
      <listitem>
       <para>
        Disable or enable all triggers belonging to the foreign table except
        for internally generated triggers.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">parent_table</replaceable></term>
      <listitem>
       <para>
        A parent table to associate or de-associate with this foreign table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_owner</replaceable></term>
      <listitem>
       <para>
        The user name of the new owner of the table.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><replaceable class="parameter">new_schema</replaceable></term>
      <listitem>
       <para>
        The name of the schema to which the table will be moved.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

   <para>
    The key word <literal>COLUMN</literal> is noise and can be omitted.
   </para>

   <para>
    Consistency with the foreign server is not checked when a column is added
    or removed with <literal>ADD COLUMN</literal> or
    <literal>DROP COLUMN</literal>, a <literal>NOT NULL</literal>
    or <literal>CHECK</literal> constraint is added, or a column type is changed
    with <literal>SET DATA TYPE</literal>.  It is the user's responsibility to ensure
    that the table definition matches the remote side.
   </para>

   <para>
    Refer to <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link> for a further description of valid
    parameters.
   </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   To mark a column as not-null:
<programlisting>
ALTER FOREIGN TABLE distributors ALTER COLUMN street SET NOT NULL;
</programlisting>
  </para>

  <para>
   To change options of a foreign table:
<programlisting>
ALTER FOREIGN TABLE myschema.distributors OPTIONS (ADD opt1 'value', SET opt2 'value2', DROP opt3);
</programlisting></para>

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   The forms <literal>ADD</literal>, <literal>DROP</literal>,
   and <literal>SET DATA TYPE</literal>
   conform with the SQL standard.  The other forms are
   <productname>PostgreSQL</productname> extensions of the SQL standard.
   Also, the ability to specify more than one manipulation in a single
   <command>ALTER FOREIGN TABLE</command> command is an extension.
  </para>

  <para>
   <command>ALTER FOREIGN TABLE DROP COLUMN</command> can be used to drop the only
   column of a foreign table, leaving a zero-column table.  This is an
   extension of SQL, which disallows zero-column foreign tables.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-createforeigntable"/></member>
   <member><xref linkend="sql-dropforeigntable"/></member>
  </simplelist>
 </refsect1>
</refentry>
