name       text,
  population real,
  elevation  int     -- (in ft)
);

CREATE VIEW cities AS
  SELECT name, population, elevation FROM capitals
    UNION
  SELECT name, population, elevation FROM non_capitals;
</programlisting>

    This works OK as far as querying goes, but it gets ugly when you
    need to update several rows, for one thing.
   </para>

   <para>
    A better solution is this:

<programlisting>
CREATE TABLE cities (
  name       text,
  population real,
  elevation  int     -- (in ft)
);

CREATE TABLE capitals (
  state      char(2) UNIQUE NOT NULL
) INHERITS (cities);
</programlisting>
   </para>

   <para>
    In this case, a row of <classname>capitals</classname>
    <firstterm>inherits</firstterm> all columns (<structfield>name</structfield>,
    <structfield>population</structfield>, and <structfield>elevation</structfield>) from its
    <firstterm>parent</firstterm>, <classname>cities</classname>.  The
    type of the column <structfield>name</structfield> is
    <type>text</type>, a native <productname>PostgreSQL</productname>
    type for variable length character strings.  The
    <classname>capitals</classname> table has
    an additional column, <structfield>state</structfield>, which shows its
    state abbreviation.  In
    <productname>PostgreSQL</productname>, a table can inherit from
    zero or more other tables.
   </para>

   <para>
    For example, the  following  query finds the  names  of  all  cities,
    including  state capitals, that are located at an elevation
    over 500 feet:

<programlisting>
SELECT name, elevation
  FROM cities
  WHERE elevation &gt; 500;
</programlisting>

    which returns:

<screen>
   name    | elevation
-----------+-----------
 Las Vegas |      2174
 Mariposa  |      1953
 Madison   |       845
(3 rows)
</screen>
   </para>

   <para>
    On the other hand, the  following  query  finds
    all  the cities that are not state capitals and
    are situated at an elevation over 500 feet:

<programlisting>
SELECT name, elevation
    FROM ONLY cities
    WHERE elevation &gt; 500;
</programlisting>

<screen>
   name    | elevation
-----------+-----------
 Las Vegas |      2174
 Mariposa  |      1953
(2 rows)
</screen>
   </para>

   <para>
    Here the <literal>ONLY</literal> before <literal>cities</literal>
    indicates that the query should be run over only the
    <classname>cities</classname> table, and not tables below
    <classname>cities</classname> in the inheritance hierarchy.  Many
    of the commands that we have already discussed &mdash;
    <command>SELECT</command>, <command>UPDATE</command>, and
    <command>DELETE</command> &mdash; support this <literal>ONLY</literal>
    notation.
   </para>

   <note>
    <para>
     Although inheritance is frequently useful, it has not been integrated
     with unique constraints or foreign keys, which limits its usefulness.
     See <xref linkend="ddl-inherit"/> for more detail.
    </para>
   </note>
  </sect1>


  <sect1 id="tutorial-conclusion">
   <title>Conclusion</title>

   <para>
    <productname>PostgreSQL</productname> has many features not
    touched upon in this tutorial introduction, which has been
    oriented toward newer users of <acronym>SQL</acronym>.  These
    features are discussed in more detail in the remainder of this
    book.
   </para>

   <para>
    If you feel you need more introductory material, please visit the PostgreSQL
    <ulink url="https://www.postgresql.org">web site</ulink>
    for links to more resources.
   </para>
  </sect1>
 </chapter>