<<   >>   ~=   <@   <<|   |>>
</synopsis>

   (See <xref linkend="functions-geometry"/> for the meaning of
   these operators.)
   The SP-GiST operator classes included in the standard distribution are
   documented in <xref linkend="spgist-builtin-opclasses-table"/>.
   For more information see <xref linkend="spgist"/>.
  </para>

  <para>
   Like GiST, SP-GiST supports <quote>nearest-neighbor</quote> searches.
   For SP-GiST operator classes that support distance ordering, the
   corresponding operator is listed in the <quote>Ordering Operators</quote>
   column in <xref linkend="spgist-builtin-opclasses-table"/>.
  </para>
  </sect2>

  <sect2 id="indexes-types-gin">
   <title>GIN</title>

   <indexterm>
    <primary>index</primary>
    <secondary>GIN</secondary>
   </indexterm>
   <indexterm>
    <primary>GIN</primary>
    <see>index</see>
   </indexterm>

  <para>
   GIN indexes are <quote>inverted indexes</quote> which are appropriate for
   data values that contain multiple component values, such as arrays.  An
   inverted index contains a separate entry for each component value, and
   can efficiently handle queries that test for the presence of specific
   component values.
  </para>

  <para>
   Like GiST and SP-GiST, GIN can support
   many different user-defined indexing strategies, and the particular
   operators with which a GIN index can be used vary depending on the
   indexing strategy.
   As an example, the standard distribution of
   <productname>PostgreSQL</productname> includes a GIN operator class
   for arrays, which supports indexed queries using these operators:

<synopsis>
&lt;@ &nbsp; @&gt; &nbsp; = &nbsp; &amp;&amp;
</synopsis>

   (See <xref linkend="functions-array"/> for the meaning of
   these operators.)
   The GIN operator classes included in the standard distribution are
   documented in <xref linkend="gin-builtin-opclasses-table"/>.
   Many other GIN operator
   classes are available in the <literal>contrib</literal> collection or as separate
   projects.  For more information see <xref linkend="gin"/>.
  </para>
  </sect2>

  <sect2 id="indexes-types-brin">
   <title>BRIN</title>

   <indexterm>
    <primary>index</primary>
    <secondary>BRIN</secondary>
   </indexterm>
   <indexterm>
    <primary>BRIN</primary>
    <see>index</see>
   </indexterm>

  <para>
   BRIN indexes (a shorthand for Block Range INdexes) store summaries about
   the values stored in consecutive physical block ranges of a table.
   Thus, they are most effective for columns whose values are well-correlated
   with the physical order of the table rows.
   Like GiST, SP-GiST and GIN,
   BRIN can support many different indexing strategies,
   and the particular operators with which a BRIN index can be used
   vary depending on the indexing strategy.
   For data types that have a linear sort order, the indexed data
   corresponds to the minimum and maximum values of the
   values in the column for each block range.  This supports indexed queries
   using these operators:

<synopsis>
&lt; &nbsp; &lt;= &nbsp; = &nbsp; &gt;= &nbsp; &gt;
</synopsis>

   The BRIN operator classes included in the standard distribution are
   documented in <xref linkend="brin-builtin-opclasses-table"/>.
   For more information see <xref linkend="brin"/>.
  </para>
  </sect2>
 </sect1>


 <sect1 id="indexes-multicolumn">
  <title>Multicolumn Indexes</title>

  <indexterm zone="indexes-multicolumn">
   <primary>index</primary>
   <secondary>multicolumn</secondary>
  </indexterm>

  <para>
   An index can be defined on more than one column of a table.  For example, if
   you have a table of this form:
<programlisting>
CREATE TABLE test2 (
  major int,
  minor int,
  name varchar
);
</programlisting>
   (say, you keep your <filename class="directory">/dev</filename>
   directory in a database...) and you frequently issue queries like:
<programlisting>
SELECT name FROM test2 WHERE major = <replaceable>constant</replaceable>