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<!-- $PostgreSQL: pgsql/doc/src/sgml/intarray.sgml,v 1.5 2007/12/10 05:32:51 tgl Exp $ -->
<sect1 id="intarray">
<title>intarray</title>
<indexterm zone="intarray">
<primary>intarray</primary>
</indexterm>
<para>
The <filename>intarray</> module provides a number of useful functions
and operators for manipulating one-dimensional arrays of integers.
There is also support for indexed searches using some of the operators.
</para>
<sect2>
<title><filename>intarray</> Functions and Operators</title>
<table id="intarray-func-table">
<title><filename>intarray</> Functions</title>
<tgroup cols="5">
<thead>
<row>
<entry>Function</entry>
<entry>Return Type</entry>
<entry>Description</entry>
<entry>Example</entry>
<entry>Result</entry>
</row>
</thead>
<tbody>
<row>
<entry><function>icount(int[])</function></entry>
<entry><type>int</type></entry>
<entry>number of elements in array</entry>
<entry><literal>icount('{1,2,3}'::int[])</literal></entry>
<entry><literal>3</literal></entry>
</row>
<row>
<entry><function>sort(int[], text dir)</function></entry>
<entry><type>int[]</type></entry>
<entry>sort array &mdash; <parameter>dir</> must be <literal>asc</> or <literal>desc</></entry>
<entry><literal>sort('{1,2,3}'::int[], 'desc')</literal></entry>
<entry><literal>{3,2,1}</literal></entry>
</row>
<row>
<entry><function>sort(int[])</function></entry>
<entry><type>int[]</type></entry>
<entry>sort in ascending order</entry>
<entry><literal>sort(array[11,77,44])</literal></entry>
<entry><literal>{11,44,77}</literal></entry>
</row>
<row>
<entry><function>sort_asc(int[])</function></entry>
<entry><type>int[]</type></entry>
<entry>sort in ascending order</entry>
<entry><literal></literal></entry>
<entry><literal></literal></entry>
</row>
<row>
<entry><function>sort_desc(int[])</function></entry>
<entry><type>int[]</type></entry>
<entry>sort in descending order</entry>
<entry><literal></literal></entry>
<entry><literal></literal></entry>
</row>
<row>
<entry><function>uniq(int[])</function></entry>
<entry><type>int[]</type></entry>
<entry>remove adjacent duplicates</entry>
<entry><literal>uniq(sort('{1,2,3,2,1}'::int[]))</literal></entry>
<entry><literal>{1,2,3}</literal></entry>
</row>
<row>
<entry><function>idx(int[], int item)</function></entry>
<entry><type>int</type></entry>
<entry>index of first element matching <parameter>item</> (0 if none)</entry>
<entry><literal>idx(array[11,22,33,22,11], 22)</literal></entry>
<entry><literal>2</literal></entry>
</row>
<row>
<entry><function>subarray(int[], int start, int len)</function></entry>
<entry><type>int[]</type></entry>
<entry>portion of array starting at position <parameter>start</>, len <parameter>elements</></entry>
<entry><literal>subarray('{1,2,3,2,1}'::int[], 2, 3)</literal></entry>
<entry><literal>{2,3,2}</literal></entry>
</row>
<row>
<entry><function>subarray(int[], int start)</function></entry>
<entry><type>int[]</type></entry>
<entry>portion of array starting at position <parameter>start</></entry>
<entry><literal>subarray('{1,2,3,2,1}'::int[], 2)</literal></entry>
<entry><literal>{2,3,2,1}</literal></entry>
</row>
<row>
<entry><function>intset(int)</function></entry>
<entry><type>int[]</type></entry>
<entry>make single-element array</entry>
<entry><literal>intset(42)</literal></entry>
<entry><literal>{42}</literal></entry>
</row>
</tbody>
</tgroup>
</table>
<table id="intarray-op-table">
<title><filename>intarray</> Operators</title>
<tgroup cols="3">
<thead>
<row>
<entry>Operator</entry>
<entry>Returns</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>int[] &amp;&amp; int[]</literal></entry>
<entry><type>boolean</type></entry>
<entry>overlap &mdash; <literal>true</> if arrays have at least one common element</entry>
</row>
<row>
<entry><literal>int[] @&gt; int[]</literal></entry>
<entry><type>boolean</type></entry>
<entry>contains &mdash; <literal>true</> if left array contains right array</entry>
</row>
<row>
<entry><literal>int[] &lt;@ int[]</literal></entry>
<entry><type>boolean</type></entry>
<entry>contained &mdash; <literal>true</> if left array is contained in right array</entry>
</row>
<row>
<entry><literal># int[]</literal></entry>
<entry><type>int</type></entry>
<entry>number of elements in array</entry>
</row>
<row>
<entry><literal>int[] # int</literal></entry>
<entry><type>int</type></entry>
<entry>index (same as <function>idx</> function)</entry>
</row>
<row>
<entry><literal>int[] + int</literal></entry>
<entry><type>int[]</type></entry>
<entry>push element onto array (add it to end of array)</entry>
</row>
<row>
<entry><literal>int[] + int[] </literal></entry>
<entry><type>int[]</type></entry>
<entry>array concatenation (right array added to the end of left one)</entry>
</row>
<row>
<entry><literal>int[] - int</literal></entry>
<entry><type>int[]</type></entry>
<entry>remove entries matching right argument from array</entry>
</row>
<row>
<entry><literal>int[] - int[]</literal></entry>
<entry><type>int[]</type></entry>
<entry>remove elements of right array from left</entry>
</row>
<row>
<entry><literal>int[] | int</literal></entry>
<entry><type>int[]</type></entry>
<entry>union of arguments</entry>
</row>
<row>
<entry><literal>int[] | int[]</literal></entry>
<entry><type>int[]</type></entry>
<entry>union of arrays</entry>
</row>
<row>
<entry><literal>int[] &amp; int[]</literal></entry>
<entry><type>int[]</type></entry>
<entry>intersection of arrays</entry>
</row>
<row>
<entry><literal>int[] @@ query_int</literal></entry>
<entry><type>boolean</type></entry>
<entry><literal>true</> if array satisfies query (see below)</entry>
</row>
<row>
<entry><literal>query_int ~~ int[]</literal></entry>
<entry><type>boolean</type></entry>
<entry><literal>true</> if array satisfies query (commutator of <literal>@@</>)</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
(Before PostgreSQL 8.2, the containment operators @&gt; and &lt;@ were
respectively called @ and ~. 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
datatypes!)
</para>
<para>
The <literal>@@</> and <literal>~~</> operators test whether an array
satisfies a <firstterm>query</>, which is expressed as a value of a
specialized data type <type>query_int</>. A <firstterm>query</>
consists of integer values that are checked against the elements of
the array, possibly combined using the operators <literal>&amp;</>
(AND), <literal>|</> (OR), and <literal>!</> (NOT). Parentheses
can be used as needed. For example,
the query <literal>1&amp;(2|3)</> matches arrays that contain 1
and also contain either 2 or 3.
</para>
</sect2>
<sect2>
<title>Index Support</title>
<para>
<filename>intarray</> provides index support for the
<literal>&amp;&amp;</>, <literal>@&gt;</>, <literal>&lt;@</>,
and <literal>@@</> operators, as well as regular array equality.
The implementation uses an RD-tree data structure with
built-in lossy compression.
</para>
<para>
Two GiST index operator classes are provided:
<literal>gist__int_ops</> (used by default) is suitable for
small and medium-size arrays, while
<literal>gist__intbig_ops</> uses a larger signature and is more
suitable for indexing large arrays.
</para>
<para>
There is also a non-default GIN operator class
<literal>gin__int_ops</>.
</para>
<para>
The choice between GiST and GIN indexing depends on the relative
performance characteristics of GiST and GIN, which are discussed elsewhere.
As a rule of thumb, a GIN index is faster to search than a GiST index, but
slower to build or update; so GIN is better suited for static data and GiST
for often-updated data.
</para>
</sect2>
<sect2>
<title>Example</title>
<programlisting>
-- a message can be in one or more <quote>sections</>
CREATE TABLE message (mid INT PRIMARY KEY, sections INT[], ...);
-- create specialized index
CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__int_ops);
-- 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</> contains a
benchmark test suite. To run:
</para>
<programlisting>
cd .../bench
createdb TEST
psql TEST &lt; ../_int.sql
./create_test.pl | psql TEST
./bench.pl
</programlisting>
<para>
The <filename>bench.pl</> 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@stack.net</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>
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