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<!-- 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="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><indexterm><primary>icount</primary></indexterm></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><indexterm><primary>sort</primary></indexterm></entry>
<entry><type>int[]</type></entry>
<entry>sort array &mdash; <parameter>dir</parameter> must be <literal>asc</literal> or <literal>desc</literal></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><indexterm><primary>sort_asc</primary></indexterm></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><indexterm><primary>sort_desc</primary></indexterm></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><indexterm><primary>uniq</primary></indexterm></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><indexterm><primary>idx</primary></indexterm></entry>
<entry><type>int</type></entry>
<entry>index of first element matching <parameter>item</parameter> (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><indexterm><primary>subarray</primary></indexterm></entry>
<entry><type>int[]</type></entry>
<entry>portion of array starting at position <parameter>start</parameter>, <parameter>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</parameter></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><indexterm><primary>intset</primary></indexterm></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</filename> 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</literal> 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</literal> 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</literal> 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> 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</literal> if array satisfies query (see below)</entry>
</row>
<row>
<entry><literal>query_int ~~ int[]</literal></entry>
<entry><type>boolean</type></entry>
<entry><literal>true</literal> if array satisfies query (commutator of <literal>@@</literal>)</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 parametrized 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 integer set as an array of
integer ranges. Optional integer parameter <literal>numranges</literal> of
<literal>gist__int_ops</literal> determines maximum number of ranges in
one index key. Default value of <literal>numranges</literal> is 100.
Valid values are between 1 and 253. Using larger arrays as GiST index
keys leads to more precise search (scan less fraction of index, scan less
heap pages), but larger index.
</para>
<para>
<literal>gist__intbig_ops</literal> approximates integer set as a bitmap
signature. Optional integer parameter <literal>siglen</literal> of
<literal>gist__intbig_ops</literal> determines signature length in bytes.
Default signature length is 16 bytes. Valid values of signature length
are between 1 and 2024 bytes. Longer signatures leads to more precise
search (scan less fraction of index, scan less heap pages), but 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 sigature length of 32 bytes
CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__int_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>
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