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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 just earth geometry. 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 provide output time-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 ensure compatibility to earlier versions of
- <productname>PostgreSQL</productname>
- we continue to provide <type>datetime</type>
+ To ensure an upgrade path from versions of
+ <productname>PostgreSQL</productname> earlier than 7.0,
+ we recognize <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 are some possible 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>
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Date/time details
-->
<appendix id="datetime-appendix">
<title id="datetime-appendix-title">Date/Time Support</title>
+ <para>
+ <productname>PostgreSQL</productname> uses an internal heuristic
+ parser for all date/time support. Dates and times are input as
+ strings, and are broken up into distinct fields with a preliminary
+ determination of what kind of information may be in the
+ field. Each field is interpreted and either assigned a numeric
+ value, ignored, or rejected.
+ The parser contains internal lookup tables for all textual fields,
+ including months, days of the week, and time
+ zones.
+ </para>
+
+ <para>
+ This appendix includes information on the content of these
+ lookup tables and describes the steps used by the parser to decode
+ dates and times.
+ </para>
+
+ <sect1>
+ <title>Date/Time Keywords</title>
+
+ <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>
+ </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>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </para>
+
+ <para>
+ <table tocentry="1">
+ <title><productname>PostgreSQL</productname> Field Modifiers</title>
+ <titleabbrev>Field Modifiers</titleabbrev>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Identifier</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>ABSTIME</entry>
+ <entry>Keyword ignored</entry>
+ </row>
+ <row>
+ <entry>AM</entry>
+ <entry>Time is before 12:00</entry>
+ </row>
+ <row>
+ <entry>AT</entry>
+ <entry>Keyword ignored</entry>
+ </row>
+ <row>
+ <entry>JULIAN, JD, J</entry>
+ <entry>Next field is Julian Day</entry>
+ </row>
+ <row>
+ <entry>ON</entry>
+ <entry>Keyword ignored</entry>
+ </row>
+ <row>
+ <entry>PM</entry>
+ <entry>Time is on or after after 12:00</entry>
+ </row>
+ <row>
+ <entry>T</entry>
+ <entry>Next field is time</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </para>
+
+ <para>
+ The keyword <literal>ABSTIME</literal> is ignored for historical
+ reasons; in very old releases of
+ <productname>PostgreSQL</productname> invalid <type>ABSTIME</type>
+ fields were emitted as <quote>Invalid Abstime</quote>. This is no
+ longer the case however and this keyword will likely be dropped in
+ a future release.
+ </para>
+ </sect1>
+
<sect1 id="timezones">
<title>Time Zones</title>
system interface to provide access to general, cross-timezone
information. The underlying OS <emphasis>is</emphasis> used to
provide time zone information for <emphasis>output</emphasis>, however.
+ </para>
+
+ <para>
+ The following table of time zones recognized by
+ <productname>PostgreSQL</productname> is organized by time
+ zone offset from UTC, rather than alphabetically; this is intended
+ to faciliate
+ matching local usage with recognized abreviations for cases where
+ these might differ.
<table tocentry="1">
<title><productname>PostgreSQL</productname> Recognized Time Zones</title>
<entry>+00:00</entry>
<entry>Greenwich Mean Time</entry>
</row>
+ <row>
+ <entry>UT</entry>
+ <entry>+00:00</entry>
+ <entry>Universal Time</entry>
+ </row>
+ <row>
+ <entry>UTC</entry>
+ <entry>+00:00</entry>
+ <entry>Universal Time, Coordinated</entry>
+ </row>
+ <row>
+ <entry>Z</entry>
+ <entry>+00:00</entry>
+ <entry>Same as UTC</entry>
+ </row>
+ <row>
+ <entry>ZULU</entry>
+ <entry>+00:00</entry>
+ <entry>Same as UTC</entry>
+ </row>
<row>
<entry>WET</entry>
<entry>+00:00</entry>
<substeps>
<step>
<para>
- If the token contains a colon (":"), this is a time string.
+ If the numeric token contains a colon (":"), this is a time
+ string. Include all subsequent digits and colons.
</para>
</step>
<step>
<para>
- If the token contains a dash ("-"), slash ("/"), or dot ("."),
+ If the numeric token contains a dash ("-"), slash ("/"), or
+ two or more dots ("."),
this is a date string which may have a text month.
</para>
</step>
<step>
<para>
If the token is numeric only, then it is either a single field
- or an ISO-8601 concatenated date (e.g. <literal>19990113</literal> for January 13, 1999)
+ or an ISO-8601 concatenated date
+ (e.g. <literal>19990113</literal> for January 13, 1999)
or time (e.g. 141516 for 14:15:16).
</para>
</step>
</para>
</step>
+ <step>
+ <para>
+ If four or six digits and a year has already been read, then
+ interpret as a time.
+ </para>
+ </step>
+
<step>
<para>
If four or more digits, then interpret as a year.
<step>
<para>
- If BC has been specified, negate the year and offset by one for
+ If BC has been specified, negate the year and add one for
internal storage
(there is no year zero in the Gregorian calendar, so numerically
- 1BC becomes year zero).
+ <literal>1BC</literal> becomes year zero).
</para>
</step>
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