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</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>.
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>