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Postgres FD Implementation
Commit 97b1ac1a authored by Tom Lane's avatar Tom Lane
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Update documentation to reflect the fact that we now know exactly what 

time zone names we support.
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doc/src/sgml/datatype.sgml
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$PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.146 2004/06/16 01:26:35 tgl Exp $
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<chapter id="datatype">
......@@ -1668,6 +1668,11 @@ SELECT b, char_length(b) FROM test2;
</tbody>
</tgroup>
</table>
<para>
Refer to <xref linkend="datetime-appendix"> for a list of
time zone names that are recognized for input.
</para>
</sect3>
<sect3>
......@@ -1687,9 +1692,11 @@ SELECT b, char_length(b) FROM test2;
<para>
Valid input for the time stamp types consists of a concatenation
of a date and a time, followed by an optional
<literal>AD</literal> or <literal>BC</literal>, followed by an
optional time zone. Thus
of a date and a time, followed by an optional time zone,
followed by an optional <literal>AD</literal> or <literal>BC</literal>.
(Alternatively, <literal>AD</literal>/<literal>BC</literal> can appear
before the time zone, but this is not the preferred ordering.)
Thus
<programlisting>
1999-01-08 04:05:06
......@@ -1798,17 +1805,7 @@ January 8 04:05:06 1999 PST
</indexterm>
<para>
The following <acronym>SQL</acronym>-compatible functions can be
used as date or time values for the corresponding data type:
<literal>CURRENT_DATE</literal>, <literal>CURRENT_TIME</literal>,
<literal>CURRENT_TIMESTAMP</literal>, <literal>LOCALTIME</literal>,
<literal>LOCALTIMESTAMP</literal>. The latter four accept an
optional precision specification. (See also <xref
linkend="functions-datetime-current">.)
</para>
<para>
<productname>PostgreSQL</productname> also supports several
<productname>PostgreSQL</productname> supports several
special date/time input values for convenience, as shown in <xref
linkend="datatype-datetime-special-table">. The values
<literal>infinity</literal> and <literal>-infinity</literal>
......@@ -1874,6 +1871,18 @@ January 8 04:05:06 1999 PST
</tgroup>
</table>
<para>
The following <acronym>SQL</acronym>-compatible functions can also
be used to obtain the current time value for the corresponding data
type:
<literal>CURRENT_DATE</literal>, <literal>CURRENT_TIME</literal>,
<literal>CURRENT_TIMESTAMP</literal>, <literal>LOCALTIME</literal>,
<literal>LOCALTIMESTAMP</literal>. The latter four accept an
optional precision specification. (See also <xref
linkend="functions-datetime-current">.) Note however that these are
SQL functions and are <emphasis>not</> recognized as data input strings.
</para>
</sect3>
</sect2>
......@@ -1985,12 +1994,12 @@ January 8 04:05:06 1999 PST
<para>
<type>interval</type> output looks like the input format, except
that units like <literal>century</literal> or
<literal>wek</literal> are converted to years and days and that
<literal>week</literal> are converted to years and days and
<literal>ago</literal> is converted to an appropriate sign. In
ISO mode the output looks like
<programlisting>
<optional> <replaceable>quantity</> <replaceable>unit</> <optional> ... </> </> <optional> <replaceable>days</> </> <optional> <replaceable>hours</>:<replaceable>minutes</>:<replaceable>sekunden</> </optional>
<optional> <replaceable>quantity</> <replaceable>unit</> <optional> ... </> </> <optional> <replaceable>days</> </> <optional> <replaceable>hours</>:<replaceable>minutes</>:<replaceable>seconds</> </optional>
</programlisting>
</para>
......@@ -2017,19 +2026,13 @@ January 8 04:05:06 1999 PST
Time zones, and time-zone conventions, are influenced by
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 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> 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>.
But since time zone support is derived from the underlying operating
system time-zone capabilities, it can handle daylight-saving time
and other special behavior.
but continue to be prone to arbitrary changes, particularly with
respect to daylight-savings rules.
<productname>PostgreSQL</productname> currently supports daylight-savings
rules over the time period 1902 through 2038 (corresponding to the full
range of conventional Unix system time). Times outside that range are
taken to be in <quote>standard time</> for the selected time zone, no
matter what part of the year they fall in.
</para>
<para>
......@@ -2044,8 +2047,8 @@ January 8 04:05:06 1999 PST
Although the <type>date</type> type
does not have an associated time zone, the
<type>time</type> type can.
Time zones in the real world can have no meaning unless
associated with a date as well as a time
Time zones in the real world have little meaning unless
associated with a date as well as a time,
since the offset may vary through the year with daylight-saving
time boundaries.
</para>
......@@ -2054,8 +2057,8 @@ January 8 04:05:06 1999 PST
<listitem>
<para>
The default time zone is specified as a constant numeric offset
from <acronym>UTC</>. It is not possible to adapt to daylight-saving
time when doing date/time arithmetic across
from <acronym>UTC</>. It is therefore not possible to adapt to
daylight-saving time when doing date/time arithmetic across
<acronym>DST</acronym> boundaries.
</para>
</listitem>
......@@ -2069,34 +2072,45 @@ January 8 04:05:06 1999 PST
recommend <emphasis>not</emphasis> using the type <type>time with
time zone</type> (though it is supported by
<productname>PostgreSQL</productname> for legacy applications and
for compatibility with other <acronym>SQL</acronym>
implementations). <productname>PostgreSQL</productname> assumes
for compliance with the <acronym>SQL</acronym> standard).
<productname>PostgreSQL</productname> assumes
your local time zone for any type containing only date or time.
</para>
<para>
All dates and times are stored internally in
<acronym>UTC</acronym>. Times are converted to local time
on the database server before being sent to the client,
hence by default are in the server time zone.
All timezone-aware dates and times are stored internally in
<acronym>UTC</acronym>. They are converted to local time
in the zone specified by the <xref linkend="guc-timezone"> configuration
parameter before being displayed to the client.
</para>
<para>
There are several ways to select the time zone used by the server:
The <xref linkend="guc-timezone"> configuration parameter can
be set in the file <filename>postgresql.conf</>, or in any of the
other standard ways described in <xref linkend="runtime-config">.
There are also several special ways to set it:
<itemizedlist>
<listitem>
<para>
The <envar>TZ</envar> environment variable on the server host
is used by the server as the default time zone, if no other is
specified.
If <varname>timezone</> is not specified in
<filename>postgresql.conf</> nor as a postmaster command-line switch,
the server attempts to use the value of the <envar>TZ</envar>
environment variable as the default time zone. If <envar>TZ</envar>
is not defined or is not any of the time zone names known to
<productname>PostgreSQL</productname>, the server attempts to
determine the operating system's default time zone by checking the
behavior of the C library function <literal>localtime()</>. The
default time zone is selected as the closest match among
<productname>PostgreSQL</productname>'s known time zones.
</para>
</listitem>
<listitem>
<para>
The <xref linkend="guc-timezone"> configuration parameter can
be set in the file <filename>postgresql.conf</>.
The <acronym>SQL</acronym> command <command>SET TIME ZONE</command>
sets the time zone for the session. This is an alternative spelling
of <command>SET TIMEZONE TO</> with a more SQL-spec-compatible syntax.
</para>
</listitem>
......@@ -2108,23 +2122,9 @@ January 8 04:05:06 1999 PST
command to the server upon connection.
</para>
</listitem>
<listitem>
<para>
The <acronym>SQL</acronym> command <command>SET TIME ZONE</command>
sets the time zone for the session.
</para>
</listitem>
</itemizedlist>
</para>
<note>
<para>
If an invalid time zone is specified, the time zone becomes
<acronym>UTC</acronym> (on most systems anyway).
</para>
</note>
<para>
Refer to <xref linkend="datetime-appendix"> for a list of
available time zones.
......
doc/src/sgml/datetime.sgml
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doc/src/sgml/func.sgml
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$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.217 2004/08/10 00:55:03 tgl Exp $
PostgreSQL documentation
-->
......@@ -5027,7 +5027,7 @@ EXTRACT (<replaceable>field</replaceable> FROM <replaceable>source</replaceable>
<term><literal>century</literal></term>
<listitem>
<para>
The historical definition of a century.
The century
</para>
<screen>
......@@ -5038,10 +5038,9 @@ SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
</screen>
<para>
An historical century is a period of 100 years.
The first century starts at 0001-01-01 00:00:00 AD, although
they did not know at the time. This definition applies to all
Gregorian calendar countries. There is no number 0 century,
they did not know it at the time. This definition applies to all
Gregorian calendar countries. There is no century number 0,
you go from -1 to 1.
If you disagree with this, please write your complaint to:
......@@ -5049,9 +5048,9 @@ SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
</para>
<para>
Compatibility: if you want the previous postgres version of century,
just divide the year by 100. Note that with this definition,
century number 0 lasts 200 years.
<productname>PostgreSQL</productname> releases before 8.0 did not
follow the conventional numbering of centuries, but just returned
the year field divided by 100.
</para>
</listitem>
</varlistentry>
......@@ -5175,7 +5174,7 @@ SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
<term><literal>millennium</literal></term>
<listitem>
<para>
The conventional historical millennium.
The millennium
</para>
<screen>
......@@ -5184,9 +5183,15 @@ SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
</screen>
<para>
Years in the 1900's are in the second millennium.
Years in the 1900s are in the second millennium.
The third millennium starts January 1, 2001.
</para>
<para>
<productname>PostgreSQL</productname> releases before 8.0 did not
follow the conventional numbering of millennia, but just returned
the year field divided by 1000.
</para>
</listitem>
</varlistentry>
......@@ -5481,6 +5486,11 @@ SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
In these expressions, the desired time zone <replaceable>zone</> can be
specified either as a text string (e.g., <literal>'PST'</literal>)
or as an interval (e.g., <literal>INTERVAL '-08:00'</literal>).
In the text case, the available zone names are those shown in
<xref linkend="datetime-timezone-input-table">. (It would be useful
to support the more general names shown in
<xref linkend="datetime-timezone-set-table">, but this is not yet
implemented.)
</para>
<para>
......
doc/src/sgml/ref/set.sgml
View file @ 97b1ac1a
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$PostgreSQL: pgsql/doc/src/sgml/ref/set.sgml,v 1.85 2004/08/03 20:32:32 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/set.sgml,v 1.86 2004/08/10 00:55:08 tgl Exp $
PostgreSQL documentation
-->
......@@ -158,7 +158,7 @@ SELECT setseed(<replaceable>value</replaceable>);
for <literal>SET timezone TO <replaceable>value</></>. The
syntax <literal>SET TIME ZONE</literal> allows special syntax
for the time zone specification. Here are examples of valid
values (but note some are accepted only on some platforms):
values:
<variablelist>
<varlistentry>
......@@ -169,14 +169,6 @@ SELECT setseed(<replaceable>value</replaceable>);
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>'Portugal'</literal></term>
<listitem>
<para>
The time zone for Portugal.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>'Europe/Rome'</literal></term>
<listitem>
......@@ -216,7 +208,8 @@ SELECT setseed(<replaceable>value</replaceable>);
</variablelist>
See <xref linkend="datatype-datetime"> for more information
about time zones.
about time zones. Also, <xref linkend="datetime-appendix">
has a list of the recognized names for time zones.
</para>
</listitem>
</varlistentry>
......@@ -253,15 +246,16 @@ SET datestyle TO postgres, dmy;
</para>
<para>
Set the time zone for Berkeley, California, using quotes to
preserve the uppercase spelling of the time zone name:
Set the time zone for Berkeley, California:
<screen>
SET TIME ZONE 'PST8PDT';
SELECT current_timestamp AS today;
</screen>
</para>
today
-------------------------------
2003-04-29 15:02:01.218622-07
<para>
Set the time zone for Italy:
<screen>
SET TIME ZONE 'Europe/Rome';
</screen>
</para>
</refsect1>
......
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