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

<refentry id="SQL-ALTERFOREIGNTABLE">
 <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>

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

 <refsynopsisdiv>
<synopsis>
ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
    <replaceable class="PARAMETER">action</replaceable> [, ... ]
ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
    RENAME [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> TO <replaceable class="PARAMETER">new_column</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 ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable> [ NULL | NOT NULL ]
    DROP [ COLUMN ] [ IF EXISTS ] <replaceable class="PARAMETER">column</replaceable> [ RESTRICT | CASCADE ]
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> [ SET DATA ] TYPE <replaceable class="PARAMETER">type</replaceable>
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> { SET | DROP } NOT NULL
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> SET ( <replaceable class="PARAMETER">attribute_option</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> RESET ( <replaceable class="PARAMETER">attribute_option</replaceable> [, ... ] )
    ALTER [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> OPTIONS ( [ ADD | SET | DROP ] <replaceable class="PARAMETER">option</replaceable> ['<replaceable class="PARAMETER">value</replaceable>'] [, ... ])
    OWNER TO <replaceable class="PARAMETER">new_owner</replaceable>
    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</literal></term>
    <listitem>
     <para>
      This form adds a new column to the foreign table, using the same syntax as
      <xref linkend="SQL-CREATEFOREIGNTABLE">.
     </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</> 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>IF EXISTS</literal></term>
    <listitem>
     <para>
      Do not throw an error if the foreign table does not exist. A notice is
      issued in this case.
     </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.
     </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
      <xref linkend="sql-analyze"> operations.
      See the similar form of <xref linkend="sql-altertable">
      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 <xref linkend="sql-altertable">
      for more details.
     </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>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>

   <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>SET</>, and <literal>DROP</>
      specify the action to be performed.  <literal>ADD</> 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>

  </variablelist>
  </para>

  <para>
   All the actions except <literal>RENAME</literal> and <literal>SET SCHEMA</>
   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>
   You must own the table to use <command>ALTER FOREIGN TABLE</>.
   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 also be a direct or indirect member of 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.
       </para>
      </listitem>
     </varlistentry>

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

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

     <varlistentry>
      <term><literal>CASCADE</literal></term>
      <listitem>
       <para>
        Automatically drop objects that depend on the dropped column
        (for example, views referencing the column).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><literal>RESTRICT</literal></term>
      <listitem>
       <para>
        Refuse to drop the column if there are any dependent
        objects. This is the default behavior.
       </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</> constraint is
    added, or a column type is changed with <literal>SET DATA TYPE</>.  It is
    the user's responsibility to ensure that the table definition matches the
    remote side.
   </para>

   <para>
    Refer to <xref linkend="sql-createforeigntable"> 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 'value3');
</programlisting></para>

 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   The forms <literal>ADD</literal>, <literal>DROP</>,
   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 is an extension.
  </para>

  <para>
   <command>ALTER FOREIGN TABLE DROP COLUMN</> 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>
</refentry>
