<!-- doc/src/sgml/intarray.sgml -->

<sect1 id="intarray" xreflabel="intarray">
 <title>intarray</title>

 <indexterm zone="intarray">
  <primary>intarray</primary>
 </indexterm>

 <para>
  The <filename>intarray</filename> module provides a number of useful functions
  and operators for manipulating null-free arrays of integers.
  There is also support for indexed searches using some of the operators.
 </para>

 <para>
  All of these operations will throw an error if a supplied array contains any
  NULL elements.
 </para>

 <para>
  Many of these operations are only sensible for one-dimensional arrays.
  Although they will accept input arrays of more dimensions, the data is
  treated as though it were a linear array in storage order.
 </para>

 <para>
  This module is considered <quote>trusted</quote>, that is, it can be
  installed by non-superusers who have <literal>CREATE</literal> privilege
  on the current database.
 </para>

 <sect2>
  <title><filename>intarray</filename> Functions and Operators</title>

  <para>
   The functions provided by the <filename>intarray</filename> module
   are shown in <xref linkend="intarray-func-table"/>, the operators
   in <xref linkend="intarray-op-table"/>.
  </para>

  <table id="intarray-func-table">
   <title><filename>intarray</filename> Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para>
       <para>
        Example(s)
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>icount</primary></indexterm>
        <function>icount</function> ( <type>integer[]</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of elements in the array.
       </para>
       <para>
        <literal>icount('{1,2,3}'::integer[])</literal>
        <returnvalue>3</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>sort</primary></indexterm>
        <function>sort</function> ( <type>integer[]</type>, <parameter>dir</parameter> <type>text</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Sorts the array in either ascending or descending order.
        <parameter>dir</parameter> must be <literal>asc</literal>
        or <literal>desc</literal>.
       </para>
       <para>
        <literal>sort('{1,3,2}'::integer[], 'desc')</literal>
        <returnvalue>{3,2,1}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>sort</function> ( <type>integer[]</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para role="func_signature">
        <indexterm><primary>sort_asc</primary></indexterm>
        <function>sort_asc</function> ( <type>integer[]</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Sorts in ascending order.
       </para>
       <para>
        <literal>sort(array[11,77,44])</literal>
        <returnvalue>{11,44,77}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>sort_desc</primary></indexterm>
        <function>sort_desc</function> ( <type>integer[]</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Sorts in descending order.
       </para>
       <para>
        <literal>sort_desc(array[11,77,44])</literal>
        <returnvalue>{77,44,11}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>uniq</primary></indexterm>
        <function>uniq</function> ( <type>integer[]</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Removes adjacent duplicates.
        Often used with <function>sort</function> to remove all duplicates.
       </para>
       <para>
        <literal>uniq('{1,2,2,3,1,1}'::integer[])</literal>
        <returnvalue>{1,2,3,1}</returnvalue>
       </para>
       <para>
        <literal>uniq(sort('{1,2,3,2,1}'::integer[]))</literal>
        <returnvalue>{1,2,3}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>idx</primary></indexterm>
        <function>idx</function> ( <type>integer[]</type>, <parameter>item</parameter> <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns index of the first array element
        matching <parameter>item</parameter>, or 0 if no match.
       </para>
       <para>
        <literal>idx(array[11,22,33,22,11], 22)</literal>
        <returnvalue>2</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>subarray</primary></indexterm>
        <function>subarray</function> ( <type>integer[]</type>, <parameter>start</parameter> <type>integer</type>, <parameter>len</parameter> <type>integer</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Extracts the portion of the array starting at
        position <parameter>start</parameter>, with <parameter>len</parameter>
        elements.
       </para>
       <para>
        <literal>subarray('{1,2,3,2,1}'::integer[], 2, 3)</literal>
        <returnvalue>{2,3,2}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>subarray</function> ( <type>integer[]</type>, <parameter>start</parameter> <type>integer</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Extracts the portion of the array starting at
        position <parameter>start</parameter>.
       </para>
       <para>
        <literal>subarray('{1,2,3,2,1}'::integer[], 2)</literal>
        <returnvalue>{2,3,2,1}</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>intset</primary></indexterm>
        <function>intset</function> ( <type>integer</type> )
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Makes a single-element array.
       </para>
       <para>
        <literal>intset(42)</literal>
        <returnvalue>{42}</returnvalue>
       </para></entry>
      </row>
    </tbody>
   </tgroup>
  </table>

  <table id="intarray-op-table">
   <title><filename>intarray</filename> Operators</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Operator
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>&amp;&amp;</literal> <type>integer[]</type>
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Do arrays overlap (have at least one element in common)?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>@&gt;</literal> <type>integer[]</type>
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does left array contain right array?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>&lt;@</literal> <type>integer[]</type>
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Is left array contained in right array?
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type></type> <literal>#</literal> <type>integer[]</type>
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the number of elements in the array.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>#</literal> <type>integer</type>
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns index of the first array element
        matching the right argument, or 0 if no match.
        (Same as <function>idx</function> function.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>+</literal> <type>integer</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Adds element to end of array.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>+</literal> <type>integer[]</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Concatenates the arrays.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>-</literal> <type>integer</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Removes entries matching the right argument from the array.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>-</literal> <type>integer[]</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Removes elements of the right array from the left array.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>|</literal> <type>integer</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Computes the union of the arguments.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>|</literal> <type>integer[]</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Computes the union of the arguments.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>&amp;</literal> <type>integer[]</type>
        <returnvalue>integer[]</returnvalue>
       </para>
       <para>
        Computes the intersection of the arguments.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>integer[]</type> <literal>@@</literal> <type>query_int</type>
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does array satisfy query?  (see below)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <type>query_int</type> <literal>~~</literal> <type>integer[]</type>
        <returnvalue>boolean</returnvalue>
       </para>
       <para>
        Does array satisfy query?  (commutator of <literal>@@</literal>)
       </para></entry>
      </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   (Before PostgreSQL 8.2, the containment operators <literal>@&gt;</literal> and
   <literal>&lt;@</literal> were respectively called <literal>@</literal> and <literal>~</literal>.
   These names are still available, but are deprecated and will eventually be
   retired.  Notice that the old names are reversed from the convention
   formerly followed by the core geometric data types!)
  </para>

  <para>
   The operators <literal>&amp;&amp;</literal>, <literal>@&gt;</literal> and
   <literal>&lt;@</literal> are equivalent to <productname>PostgreSQL</productname>'s built-in
   operators of the same names, except that they work only on integer arrays
   that do not contain nulls, while the built-in operators work for any array
   type.  This restriction makes them faster than the built-in operators
   in many cases.
  </para>

  <para>
   The <literal>@@</literal> and <literal>~~</literal> operators test whether an array
   satisfies a <firstterm>query</firstterm>, which is expressed as a value of a
   specialized data type <type>query_int</type>.  A <firstterm>query</firstterm>
   consists of integer values that are checked against the elements of
   the array, possibly combined using the operators <literal>&amp;</literal>
   (AND), <literal>|</literal> (OR), and <literal>!</literal> (NOT).  Parentheses
   can be used as needed.  For example,
   the query <literal>1&amp;(2|3)</literal> matches arrays that contain 1
   and also contain either 2 or 3.
  </para>
 </sect2>

 <sect2>
  <title>Index Support</title>

  <para>
   <filename>intarray</filename> provides index support for the
   <literal>&amp;&amp;</literal>, <literal>@&gt;</literal>, <literal>&lt;@</literal>,
   and <literal>@@</literal> operators, as well as regular array equality.
  </para>

  <para>
   Two parameterized GiST index operator classes are provided:
   <literal>gist__int_ops</literal> (used by default) is suitable for
   small- to medium-size data sets, while
   <literal>gist__intbig_ops</literal> uses a larger signature and is more
   suitable for indexing large data sets (i.e., columns containing
   a large number of distinct array values).
   The implementation uses an RD-tree data structure with
   built-in lossy compression.
  </para>

  <para>
   <literal>gist__int_ops</literal> approximates an integer set as an array of
   integer ranges.  Its optional integer parameter <literal>numranges</literal>
   determines the maximum number of ranges in
   one index key.  The default value of <literal>numranges</literal> is 100.
   Valid values are between 1 and 253.  Using larger arrays as GiST index
   keys leads to a more precise search (scanning a smaller fraction of the index and
   fewer heap pages), at the cost of a larger index.
  </para>

  <para>
   <literal>gist__intbig_ops</literal> approximates an integer set as a bitmap
   signature.  Its optional integer parameter <literal>siglen</literal>
   determines the signature length in bytes.
   The default signature length is 16 bytes.  Valid values of signature length
   are between 1 and 2024 bytes.  Longer signatures lead to a more precise
   search (scanning a smaller fraction of the index and fewer heap pages), at
   the cost of a larger index.
  </para>

  <para>
   There is also a non-default GIN operator class
   <literal>gin__int_ops</literal> supporting the same operators.
  </para>

  <para>
   The choice between GiST and GIN indexing depends on the relative
   performance characteristics of GiST and GIN, which are discussed elsewhere.
  </para>
 </sect2>

 <sect2>
  <title>Example</title>

<programlisting>
-- a message can be in one or more <quote>sections</quote>
CREATE TABLE message (mid INT PRIMARY KEY, sections INT[], ...);

-- create specialized index with signature length of 32 bytes
CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__intbig_ops (siglen = 32));

-- select messages in section 1 OR 2 - OVERLAP operator
SELECT message.mid FROM message WHERE message.sections &amp;&amp; '{1,2}';

-- select messages in sections 1 AND 2 - CONTAINS operator
SELECT message.mid FROM message WHERE message.sections @&gt; '{1,2}';

-- the same, using QUERY operator
SELECT message.mid FROM message WHERE message.sections @@ '1&amp;2'::query_int;
</programlisting>
 </sect2>

 <sect2>
  <title>Benchmark</title>

  <para>
   The source directory <filename>contrib/intarray/bench</filename> contains a
   benchmark test suite, which can be run against an installed
   <productname>PostgreSQL</productname> server.  (It also requires <filename>DBD::Pg</filename>
   to be installed.)  To run:
  </para>

<programlisting>
cd .../contrib/intarray/bench
createdb TEST
psql -c "CREATE EXTENSION intarray" TEST
./create_test.pl | psql TEST
./bench.pl
</programlisting>

  <para>
   The <filename>bench.pl</filename> script has numerous options, which
   are displayed when it is run without any arguments.
  </para>
 </sect2>

 <sect2>
  <title>Authors</title>

  <para>
   All work was done by Teodor Sigaev (<email>teodor@sigaev.ru</email>) and
   Oleg Bartunov (<email>oleg@sai.msu.su</email>). See
   <ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink> for
   additional information. Andrey Oktyabrski did a great work on adding new
   functions and operations.
  </para>
 </sect2>

</sect1>
