index, as described in <xref linkend="indexes-types">.

</para>

<para>

You can also search for specific values in an array using the <function>array_offset</>

and <function>array_offsets</> functions. The former returns the position of

the first occurrence of a value in an array; the latter returns an array with the

positions of all occurrences of the value in the array. For example:

<programlisting>

SELECT array_offset(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon');

array_offset

--------------

2

SELECT array_offsets(ARRAY[1, 4, 3, 1, 3, 4, 2, 1], 1);

array_offsets

---------------

{1,4,8}

</programlisting>

</para>

<tip>

<para>

Arrays are not sets; searching for specific array elements

<indexterm>

<primary>array_lower</primary>

</indexterm>

<indexterm>

<primary>array_offset</primary>

</indexterm>

<indexterm>

<primary>array_offsets</primary>

</indexterm>

<indexterm>

<primary>array_prepend</primary>

</indexterm>

<entry><literal>array_lower('[0:2]={1,2,3}'::int[], 1)</literal></entry>

<entry><literal>0</literal></entry>

</row>

<row>

<entry>

<literal>

<function>array_offset</function>(<type>anyarray</type>, <type>anyelement</type> <optional>, <type>int</type></optional>)

</literal>

</entry>

<entry><type>int</type></entry>

<entry>returns the offset of the first occurrence of the second

argument in the array, starting at the element indicated by the third

argument or at the first element (array must be one-dimensional)</entry>

<entry><literal>array_offset(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon')</literal></entry>

<entry><literal>2</literal></entry>

</row>

<row>

<entry>

<literal>

<function>array_offsets</function>(<type>anyarray</type>, <type>anyelement</type>)

</literal>

</entry>

<entry><type>int[]</type></entry>

<entry>returns an array of offsets of all occurrences of the second

argument in the array given as first argument (array must be

one-dimensional)</entry>

<entry><literal>array_offsets(ARRAY['A','A','B','A'], 'A')</literal></entry>

<entry><literal>{1,2,4}</literal></entry>

</row>

<row>

<entry>

<literal>

</tgroup>

</table>

<para>

In <function>array_offset</function> and <function>array_offsets</>,

each array element is compared to the searched value using

<literal>IS NOT DISTINCT FROM</literal> semantics.

</para>

<para>

In <function>array_offset</function>, <literal>NULL</literal> is returned

if the value is not found.

</para>

<para>

In <function>array_offsets</function>, <literal>NULL</literal> is returned

only if the array is <literal>NULL</literal>; if the value is not found in

the array, an empty array is returned instead.

</para>

<para>

In <function>string_to_array</function>, if the delimiter parameter is

NULL, each character in the input string will become a separate element in