Another way to do the same thing is:
<programlisting>
UPDATE tab SET h = h || hstore('c', '3');
</programlisting>
   If multiple keys are to be added or changed in one operation,
   the concatenation approach is more efficient than subscripting:
<programlisting>
UPDATE tab SET h = h || hstore(array['q', 'w'], array['11', '12']);
</programlisting>
  </para>

  <para>
   Delete a key:
<programlisting>
UPDATE tab SET h = delete(h, 'k1');
</programlisting>
  </para>

  <para>
   Convert a <type>record</type> to an <type>hstore</type>:
<programlisting>
CREATE TABLE test (col1 integer, col2 text, col3 text);
INSERT INTO test VALUES (123, 'foo', 'bar');

SELECT hstore(t) FROM test AS t;
                   hstore
---------------------------------------------
 "col1"=&gt;"123", "col2"=&gt;"foo", "col3"=&gt;"bar"
(1 row)
</programlisting>
  </para>

  <para>
   Convert an <type>hstore</type> to a predefined <type>record</type> type:
<programlisting>
CREATE TABLE test (col1 integer, col2 text, col3 text);

SELECT * FROM populate_record(null::test,
                              '"col1"=&gt;"456", "col2"=&gt;"zzz"');
 col1 | col2 | col3
------+------+------
  456 | zzz  |
(1 row)
</programlisting>
  </para>

  <para>
   Modify an existing record using the values from an <type>hstore</type>:
<programlisting>
CREATE TABLE test (col1 integer, col2 text, col3 text);
INSERT INTO test VALUES (123, 'foo', 'bar');

SELECT (r).* FROM (SELECT t #= '"col3"=&gt;"baz"' AS r FROM test t) s;
 col1 | col2 | col3
------+------+------
  123 | foo  | baz
(1 row)
</programlisting>
  </para>
 </sect2>

 <sect2 id="hstore-statistics">
  <title>Statistics</title>

  <para>
   The <type>hstore</type> type, because of its intrinsic liberality, could
   contain a lot of different keys. Checking for valid keys is the task of the
   application. The following examples demonstrate several techniques for
   checking keys and obtaining statistics.
  </para>

  <para>
   Simple example:
<programlisting>
SELECT * FROM each('aaa=&gt;bq, b=&gt;NULL, ""=&gt;1');
</programlisting>
  </para>

  <para>
   Using a table:
<programlisting>
CREATE TABLE stat AS SELECT (each(h)).key, (each(h)).value FROM testhstore;
</programlisting>
  </para>

  <para>
   Online statistics:
<programlisting>
SELECT key, count(*) FROM
  (SELECT (each(h)).key FROM testhstore) AS stat
  GROUP BY key
  ORDER BY count DESC, key;
    key    | count
-----------+-------
 line      |   883