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<chapter id="datatype">

<title id="datatype-title">Data Types</title>

<entry>date and time, including time zone</entry>

</row>

<row>

<entry><type>uuid</type></entry>

<entry></entry>

<entry>universally unique identifier</entry>

</row>

<row>

<entry><type>xml</type></entry>

<entry></entry>

</para>

</sect1>

<sect1 id="datatype-uuid">

<title><acronym>UUID</acronym> Type</title>

<indexterm zone="datatype-xml">

<primary>UUID</primary>

</indexterm>

<para>

The data type <type>uuid</type> stores Universally Unique

Identifiers (UUID) as per RFC 4122, ISO/IEC 9834-8:2005, and

related standards. (Some systems refer to this data type as

globally unique

identifier/GUID<indexterm><primary>GUID</primary></indexterm>

instead.) Such an identifier is a 128-bit quantity that is

generated by a suitable algorithm so that it is very unlikely to

be generated by anyone else in the known universe using the same

algorithm. Therefore, for distributed systems, these identifiers

provide a better uniqueness guarantee than that which can be

achieved using sequence generators, which are only unique within a

single database.

</para>

<para>

A UUID is written as a sequence of lower-case hexadecimal digits,

in several groups separated by hyphens, specifically a group of 8

digits followed by three groups of 4 digits followed by a group of

12 digits, for a total of 32 digits representing the 128 bits. An

example of a UUID in this standard form is:

<programlisting>

a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11

</programlisting>

PostgreSQL also accepts the following alternative forms for input:

use of upper-case digits, the standard format surrounded by

braces, and omitting the hyphens. Examples are:

<programlisting>

A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11

{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}

a0eebc999c0b4ef8bb6d6bb9bd380a11

</programlisting>

Output is always in the standard form.

</para>

</sect1>

<sect1 id="datatype-xml">

<title><acronym>XML</> Type</title>