diff --git a/doc/src/sgml/ref/alter_foreign_table.sgml b/doc/src/sgml/ref/alter_foreign_table.sgml
index c2ebdac..af7d5fa 100644
*** a/doc/src/sgml/ref/alter_foreign_table.sgml
--- b/doc/src/sgml/ref/alter_foreign_table.sgml
*************** ALTER FOREIGN TABLE <replaceable class="
*** 32,38 ****
  
  <phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>
  
!     ADD [ COLUMN ] <replaceable class="PARAMETER">column</replaceable> <replaceable class="PARAMETER">type</replaceable>
      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
--- 32,38 ----
  
  <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 FOREIGN TABLE <replaceable class="
*** 125,131 ****
      <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 the column of the foreign table.
        <literal>ADD</>, <literal>SET</>, and <literal>DROP</>
        specify the action to be performed.  <literal>ADD</> is assumed
        if no operation is explicitly specified.  Option names must be
--- 125,131 ----
      <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.
        <literal>ADD</>, <literal>SET</>, and <literal>DROP</>
        specify the action to be performed.  <literal>ADD</> is assumed
        if no operation is explicitly specified.  Option names must be
*************** ALTER FOREIGN TABLE <replaceable class="
*** 150,157 ****
     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 add the table as a new child of a parent table, you must own the
-    parent table as well.
     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
--- 150,155 ----
*************** ALTER FOREIGN TABLE <replaceable class="
*** 260,269 ****
     </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 system <literal>oid</> column is added
!     or removed, a <literal>CHECK</> or <literal>NOT NULL</> constraint is
      added, or 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.
--- 258,266 ----
     </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>, <literal>NOT NULL</> constraint is
      added, or 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.
diff --git a/doc/src/sgml/ref/create_foreign_table.sgml b/doc/src/sgml/ref/create_foreign_table.sgml
index ad91072..50d8628 100644
*** a/doc/src/sgml/ref/create_foreign_table.sgml
--- b/doc/src/sgml/ref/create_foreign_table.sgml
*************** CREATE FOREIGN TABLE [ IF NOT EXISTS ] <
*** 94,100 ****
      <listitem>
       <para>
        The data type of the column. This can include array
!       specifiers. For more information on the data types supported by
        <productname>PostgreSQL</productname>, refer to <xref
        linkend="datatype">.
       </para>
--- 94,106 ----
      <listitem>
       <para>
        The data type of the column. This can include array
!       specifiers.
!       Unlike an ordinary table, default values cannot be used on a foreign
!       tables. Serial and bigserial implicitly set default value on the column,
!       therefore they cannot be used on a foreign table.
!      </para>
!      <para>
!       For more information on the data types supported by
        <productname>PostgreSQL</productname>, refer to <xref
        linkend="datatype">.
       </para>
*************** CREATE FOREIGN TABLE [ IF NOT EXISTS ] <
*** 107,112 ****
--- 113,130 ----
       <para>
        The column is not allowed to contain null values.
       </para>
+      <para>
+       Note that defining <literal>NOT NULL</> constraint on a column doesn't
+       guarantee that the data on the foreign side don't include any null value.
+       This means that query results might include null values even if the
+       column was defined as <literal>NOT NULL</>. To ensure the integrity of
+       query result, FDW needs to throw an error when invalid data was returned
+       from the foreign server.
+      </para>
+      <para>
+       At present, <literal>NOT NULL</> constraint is used only for query plan
+       optimization.
+      </para>
      </listitem>
     </varlistentry>