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Documentation for UUID type

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Peter Eisentraut 2007-04-20 21:51:46 +00:00
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doc/src/sgml/datatype.sgml
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<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.196 2007/04/17 17:30:34 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.197 2007/04/20 21:51:46 petere Exp $ -->
<chapter id="datatype">
<title id="datatype-title">Data Types</title>
@ -234,6 +234,12 @@
<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>
@ -3199,6 +3205,49 @@ SELECT * FROM test;
</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>