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<chapter id="datatype">

<para>

Time zones, and time-zone conventions, are influenced by

political decisions, not just geometry. Time zones around the

political decisions, not justearthgeometry. Time zones around the

world became somewhat standardized during the 1900's,

but continue to be prone to arbitrary changes.

<productname>PostgreSQL</productname> uses your operating

system's underlying features to provide time-zone

system's underlying features to provideoutputtime-zone

support, and these systems usually contain information for only

the time period 1902 through 2038 (corresponding to the full

range of conventional Unix system time).

<type>timestamp with time zone</type> will use time zone

information only within that year range, and assumes that times

are in UTC outside that range.

<type>timestamp with time zone</type> and <type>time with time

zone</type> will use time zone

information only within that year range, and assume that times

outside that range are in <acronym>UTC</acronym>.

</para>

<para>

To ensurecompatibility to earlier versions of

<productname>PostgreSQL</productname>

wecontinue to provide <type>datetime</type>

To ensurean upgrade path from versions of

<productname>PostgreSQL</productname>earlier than 7.0,

werecognize <type>datetime</type>

(equivalent to <type>timestamp</type>) and

<type>timespan</type> (equivalent to <type>interval</type>),

however support for these is now restricted to having an

<type>timespan</type> (equivalent to <type>interval</type>).

These types are

now restricted to having an

implicit translation to <type>timestamp</type> and

<type>interval</type>, and these name mappings will be removed in

the next version.

<type>interval</type>, and

support for these will be removed in the next release of

<productname>PostgreSQL</productname> (likely named 7.3).

</para>

<para>

The types <type>abstime</type>

and <type>reltime</type> are lower precision types which are used internally.

You are discouraged from using any of these types in new

<acronym>SQL</acronym> standard requires.

See <xref linkend="datetime-appendix">

for the exact parsing rules of date/time input and for the

recognized time zones.

recognized text fields including months, days of the week, and

time zones.

</para>

<para>

</indexterm>

<para>

The following are possible inputs for the <type>date</type> type.

The following aresomepossible inputs for the <type>date</type> type.

<table tocentry="1">

<title>Date Input</title>

<entry>Year and day of year</entry>

</row>

<row>

<entry>January 8, 99 BC</entry>

<entry>Year 99 before the Common Era</entry>

</row>

</tbody>

</tgroup>

</table>

</para>

<para>

<table tocentry="1">

<title>Month Abbreviations</title>

<tgroup cols="2">

<thead>

<row>

<entry>Month</entry>

<entry>Abbreviations</entry>

</row>

</thead>

<tbody>

<row>

<entry>April</entry>

<entry>Apr</entry>

</row>

<row>

<entry>August</entry>

<entry>Aug</entry>

</row>

<row>

<entry>December</entry>

<entry>Dec</entry>

</row>

<row>

<entry>February</entry>

<entry>Feb</entry>

</row>

<row>

<entry>January</entry>

<entry>Jan</entry>

</row>

<row>

<entry>July</entry>

<entry>Jul</entry>

</row>

<row>

<entry>June</entry>

<entry>Jun</entry>

</row>

<row>

<entry>March</entry>

<entry>Mar</entry>

</row>

<row>

<entry>November</entry>

<entry>Nov</entry>

</row>

<row>

<entry>October</entry>

<entry>Oct</entry>

</row>

<row>

<entry>September</entry>

<entry>Sep, Sept</entry>

</row>

</tbody>

</tgroup>

</table>

<note>

<para>

The month <literal>May</literal> has no explicit abbreviation, for obvious reasons.

</para>

</note>

</para>

<para>

<table tocentry="1">

<title>Day of the Week Abbreviations</title>

<tgroup cols="2">

<thead>

<row>

<entry>Day</entry>

<entry>Abbreviation</entry>

<entry>J2451187</entry>

<entry>Julian day</entry>

</row>

</thead>

<tbody>

<row>

<entry>Sunday</entry>

<entry>Sun</entry>

</row>

<row>

<entry>Monday</entry>

<entry>Mon</entry>

</row>

<row>

<entry>Tuesday</entry>

<entry>Tue, Tues</entry>

</row>

<row>

<entry>Wednesday</entry>

<entry>Wed, Weds</entry>

</row>

<row>

<entry>Thursday</entry>

<entry>Thu, Thur, Thurs</entry>

</row>

<row>

<entry>Friday</entry>

<entry>Fri</entry>

</row>

<row>

<entry>Saturday</entry>

<entry>Sat</entry>

<entry>January 8, 99 BC</entry>

<entry>Year 99 before the Common Era</entry>

</row>

</tbody>

</tgroup>

<entry>04:05 PM</entry>

<entry>Same as 16:05; input hour must be <= 12</entry>

</row>

<row>

<entry>z</entry>

<entry>Same as 00:00:00</entry>

</row>

<row>

<entry>zulu</entry>

<entry>Same as 00:00:00</entry>

</row>

<row>

<entry>allballs</entry>

<entry>Same as 00:00:00</entry>