contain key?
       </para>
       <para>
        <literal>exist('a=&gt;1', 'a')</literal>
        <returnvalue>t</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>defined</primary></indexterm>
        <function>defined</function> ( <type>hstore</type>, <type>text</type> )
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does <type>hstore</type> contain a non-<literal>NULL</literal> value
        for key?
       </para>
       <para>
        <literal>defined('a=&gt;NULL', 'a')</literal>
        <returnvalue>f</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>delete</primary></indexterm>
        <function>delete</function> ( <type>hstore</type>, <type>text</type> )
        <returnvalue>hstore</returnvalue>
       </para>
       <para>
        Deletes pair with matching key.
       </para>
       <para>
        <literal>delete('a=&gt;1,b=&gt;2', 'b')</literal>
        <returnvalue>"a"=&gt;"1"</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>delete</function> ( <type>hstore</type>, <type>text[]</type> )
        <returnvalue>hstore</returnvalue>
       </para>
       <para>
        Deletes pairs with matching keys.
       </para>
       <para>
        <literal>delete('a=&gt;1,b=&gt;2,c=&gt;3', ARRAY['a','b'])</literal>
        <returnvalue>"c"=&gt;"3"</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>delete</function> ( <type>hstore</type>, <type>hstore</type> )
        <returnvalue>hstore</returnvalue>
       </para>
       <para>
        Deletes pairs matching those in the second argument.
       </para>
       <para>
        <literal>delete('a=&gt;1,b=&gt;2', 'a=&gt;4,b=&gt;2'::hstore)</literal>
        <returnvalue>"a"=&gt;"1"</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>populate_record</primary></indexterm>
        <function>populate_record</function> ( <type>anyelement</type>, <type>hstore</type> )
        <returnvalue>anyelement</returnvalue>
       </para>
       <para>
        Replaces fields in the left operand (which must be a composite type)
        with matching values from <type>hstore</type>.
       </para>
       <para>
        <literal>populate_record(ROW(1,2), 'f1=>42'::hstore)</literal>
        <returnvalue>(42,2)</returnvalue>
       </para></entry>
      </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   In addition to these operators and functions, values of
   the <type>hstore</type> type can be subscripted, allowing them to act
   like associative arrays.  Only a single subscript of type <type>text</type>
   can be specified; it is interpreted as a key and the corresponding
   value is fetched or stored.  For example,

<programlisting>
CREATE TABLE mytable (h hstore);
INSERT INTO mytable VALUES ('a=>b, c=>d');
SELECT h['a'] FROM mytable;
 h
---
 b
(1 row)

UPDATE mytable SET h['c'] = 'new';
SELECT h FROM mytable;
          h
----------------------
 "a"=>"b", "c"=>"new"
(1 row)
</programlisting>

   A subscripted fetch returns <literal>NULL</literal> if the subscript
   is <literal>NULL</literal> or that key does not exist in
   the <type>hstore</type>.  (Thus, a subscripted fetch is not greatly
   different from the <literal>-&gt;</literal> operator.)
   A subscripted update fails if the subscript is <literal>NULL</literal>;
   otherwise, it replaces the value for that key, adding an entry to
   the <type>hstore</type> if the key does not already exist.
  </para>
 </sect2>

 <sect2 id="hstore-indexes">
  <title>Indexes</title>

  <para>
   <type>hstore</type>