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-$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.108 2002/11/15 03:11:15 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.109 2002/11/21 23:31:20 tgl Exp $
-->
<chapter id="datatype">
<secondary>data type</secondary>
</indexterm>
+ <indexterm>
+ <primary>timestamp with time zone</primary>
+ <secondary>data type</secondary>
+ </indexterm>
+
<indexterm>
<primary>timestamp without time zone</primary>
<secondary>data type</secondary>
</indexterm>
<para>
- Time stamp types exist as <type>timestamp [
- (<replaceable>p</replaceable>) ]</type>, <type>timestamp [
+ The time stamp types are <type>timestamp [
(<replaceable>p</replaceable>) ] without time zone</type> and
- <type>timestamp [ (<replaceable>p</replaceable>) ] without time
- zone</type>. A plain <type>timestamp</type> is equivalent to
- <type>timestamp without timezone</type>.
+ <type>timestamp [ (<replaceable>p</replaceable>) ] with time
+ zone</type>. Writing just <type>timestamp</type> is equivalent to
+ <type>timestamp without time zone</type>.
+ </para>
+
+ <note>
+ <para>
+ Prior to <productname>PostgreSQL</productname> 7.3, writing just
+ <type>timestamp</type> was equivalent to <type>timestamp with time
+ zone</type>. This was changed for SQL spec compliance.
</para>
+ </note>
<para>
Valid input for the time stamp types consists of a concatenation
<para>
For <type>timestamp without time zone</type>, any explicit time
- zone specified in the input is silently swallowed. That is, the
+ zone specified in the input is silently ignored. That is, the
resulting date/time value is derived from the explicit date/time
fields in the input value, and is not adjusted for time zone.
</para>
+ <para>
+ For <type>timestamp with time zone</type>, the internally stored
+ value is always in UTC (GMT). An input value that has an explicit
+ time zone specified is converted to UTC using the appropriate offset
+ for that time zone. If no time zone is stated in the input string,
+ then it is assumed to be in the time zone indicated by the system's
+ <varname>TimeZone</> parameter, and is converted to UTC using the
+ offset for the <varname>TimeZone</> zone.
+ </para>
+
+ <para>
+ When a <type>timestamp with time
+ zone</type> value is output, it is always converted from UTC to the
+ current <varname>TimeZone</> zone, and displayed as local time in that
+ zone. To see the time in another time zone, either change
+ <varname>TimeZone</> or use the <literal>AT TIME ZONE</> construct
+ (see <xref linkend="functions-datetime-zoneconvert">).
+ </para>
+
+ <para>
+ Conversions between <type>timestamp without time zone</type> and
+ <type>timestamp with time zone</type> normally assume that the
+ <type>timestamp without time zone</type> value should be taken or given
+ as <varname>TimeZone</> local time. A different zone reference can
+ be specified for the conversion using <literal>AT TIME ZONE</>.
+ </para>
+
<table tocentry="1" id="datatype-timezone-table">
<title>Time Zone Input</title>
<tgroup cols="2">
<para>
The following <acronym>SQL</acronym>-compatible functions can be
used as date or time
- input for the corresponding data type: <literal>CURRENT_DATE</literal>,
+ values for the corresponding data type: <literal>CURRENT_DATE</literal>,
<literal>CURRENT_TIME</literal>,
<literal>CURRENT_TIMESTAMP</literal>. The latter two accept an
- optional precision specification. (See also <xref linkend="functions-datetime">.)
+ optional precision specification. (See also <xref linkend="functions-datetime-current">.)
</para>
<para>
<productname>PostgreSQL</productname> also supports several
- special constants for convenience, shown in <xref
- linkend="datatype-datetime-special-table">.
+ 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>
+ are specially represented inside the system and will be displayed
+ the same way; but the others are simply notational shorthands
+ that will be converted to ordinary date/time values when read.
</para>
<table id="datatype-datetime-special-table">
- <title>Special Date/Time Constants</title>
+ <title>Special Date/Time Inputs</title>
<tgroup cols="2">
<thead>
<row>
- <entry>Constant</entry>
+ <entry>Input string</entry>
<entry>Description</entry>
</row>
</thead>
</row>
<row>
<entry><literal>infinity</literal></entry>
- <entry>later than other valid times</entry>
+ <entry>later than all other timestamps (not available for
+ type <type>date</>)</entry>
</row>
<row>
<entry><literal>-infinity</literal></entry>
- <entry>earlier than other valid times</entry>
- </row>
- <row>
- <entry><literal>invalid</literal></entry>
- <entry>illegal entry</entry>
+ <entry>earlier than all other timestamps (not available for
+ type <type>date</>)</entry>
</row>
<row>
<entry><literal>now</literal></entry>
</para>
<para>
- There are several ways to affect the time-zone behavior:
+ There are several ways to select the time zone used by the server:
<itemizedlist>
<listitem>
<para>
The <envar>TZ</envar> environment variable on the server host
- is used by the server as the default time zone.
+ is used by the server as the default time zone, if no other is
+ specified.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ The <varname>timezone</varname> configuration parameter can be
+ set in <filename>postgresql.conf</>.
</para>
</listitem>
sets the time zone for the session.
</para>
</listitem>
-
- <listitem>
- <para>
- The construct
-<programlisting>
-<replaceable>timestamp</replaceable> AT TIME ZONE '<replaceable>zone</replaceable>'
-</programlisting>
- where <replaceable>zone</replaceable> can be specified as a
- text time zone (e.g., <literal>'PST'</literal>) or as an
- interval (e.g., <literal>INTERVAL '-08:00'</literal>).
- </para>
- </listitem>
</itemizedlist>
</para>
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-$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.130 2002/11/11 20:14:02 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.131 2002/11/21 23:31:20 tgl Exp $
PostgreSQL documentation
-->
<literal>*</literal>, etc.). For formatting functions, refer to
<xref linkend="functions-formatting">. You should be familiar with
the background information on date/time data types (see <xref
- linkend="datatype-datetime">). The date/time operators described
- below behave similarly for types involving time zones as well as
- those without.
+ linkend="datatype-datetime">).
+ </para>
+
+ <para>
+ All the functions and operators described below that take time or timestamp
+ inputs actually come in two variants: one that takes time or timestamp
+ with time zone, and one that takes time or timestamp without time zone.
+ For brevity, these variants are not shown separately.
</para>
<table id="operators-datetime-table">
<row>
<entry><function>now</function>()</entry>
- <entry><type>timestamp</type></entry>
+ <entry><type>timestamp with time zone</type></entry>
<entry>Current date and time (equivalent to
<function>current_timestamp</function>); see <xref
linkend="functions-datetime-current">
<listitem>
<para>
For <type>date</type> and <type>timestamp</type> values, the
- number of seconds since 1970-01-01 00:00:00-00 (Result may be
- negative.); for <type>interval</type> values, the total number
+ number of seconds since 1970-01-01 00:00:00-00 (can be negative);
+ for <type>interval</type> values, the total number
of seconds in the interval
</para>
<para>
The <function>date_part</function> function is modeled on the traditional
<productname>Ingres</productname> equivalent to the
- <acronym>SQL</acronym>-function <function>extract</function>:
+ <acronym>SQL</acronym>-standard function <function>extract</function>:
<synopsis>
date_part('<replaceable>field</replaceable>', <replaceable>source</replaceable>)
</synopsis>
- Note that here the <replaceable>field</replaceable> value needs to
- be a string. The valid field values for
+ Note that here the <replaceable>field</replaceable> parameter needs to
+ be a string value, not a name. The valid field values for
<function>date_part</function> are the same as for
<function>extract</function>.
</para>
</para>
</sect2>
+ <sect2 id="functions-datetime-zoneconvert">
+ <title><function>AT TIME ZONE</function></title>
+
+ <indexterm>
+ <primary>timezone</primary>
+ <secondary>conversion</secondary>
+ </indexterm>
+
+ <para>
+ The <function>AT TIME ZONE</function> construct allows conversions
+ of timestamps to different timezones.
+ </para>
+
+ <table id="functions-datetime-zoneconvert-table">
+ <title>AT TIME ZONE Variants</title>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>Expression</entry>
+ <entry>Returns</entry>
+ <entry>Description</entry>
+ </row>
+ </thead>
+
+ <tbody>
+
+ <row>
+ <entry>
+ <type>timestamp without time zone</type>
+ <literal>AT TIME ZONE</literal>
+ <replaceable>zone</>
+ </entry>
+ <entry><type>timestamp with time zone</type></entry>
+ <entry>Convert local time in given timezone to UTC</entry>
+ </row>
+
+ <row>
+ <entry>
+ <type>timestamp with time zone</type>
+ <literal>AT TIME ZONE</literal>
+ <replaceable>zone</>
+ </entry>
+ <entry><type>timestamp without time zone</type></entry>
+ <entry>Convert UTC to local time in given timezone</entry>
+ </row>
+
+ <row>
+ <entry>
+ <type>time with time zone</type>
+ <literal>AT TIME ZONE</literal>
+ <replaceable>zone</>
+ </entry>
+ <entry><type>time with time zone</type></entry>
+ <entry>Convert local time across timezones</entry>
+ </row>
+
+ </tbody>
+ </tgroup>
+ </table>
+
+ <para>
+ In these expressions, the desired time <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>).
+ </para>
+
+ <para>
+ Examples (supposing that <varname>TimeZone</> is <literal>PST8PDT</>):
+<screen>
+SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST';
+<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 19:38:40-08</computeroutput>
+
+SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'MST';
+<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 18:38:40</computeroutput>
+</screen>
+ The first example takes a zone-less timestamp and interprets it as MST time
+ (GMT-7) to produce a UTC timestamp, which is then rotated to PST (GMT-8)
+ for display. The second example takes a timestamp specified in EST
+ (GMT-5) and converts it to local time in MST (GMT-7).
+ </para>
+
+ <para>
+ The function <function>timezone</function>(<replaceable>zone</>,
+ <replaceable>timestamp</>) is equivalent to the SQL-compliant construct
+ <replaceable>timestamp</> <literal>AT TIME ZONE</literal>
+ <replaceable>zone</>.
+ </para>
+ </sect2>
+
<sect2 id="functions-datetime-current">
<title>Current Date/Time</title>
LOCALTIME ( <replaceable>precision</replaceable> )
LOCALTIMESTAMP ( <replaceable>precision</replaceable> )
</synopsis>
+ </para>
+
+ <para>
+ <function>CURRENT_TIME</function> and
+ <function>CURRENT_TIMESTAMP</function> deliver values with time zone;
+ <function>LOCALTIME</function> and
+ <function>LOCALTIMESTAMP</function> deliver values without time zone.
+ </para>
+
+ <para>
<function>CURRENT_TIME</function>,
<function>CURRENT_TIMESTAMP</function>,
<function>LOCALTIME</function>, and
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/utils/adt/date.c,v 1.73 2002/09/21 19:52:41 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/utils/adt/date.c,v 1.74 2002/11/21 23:31:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
text *zone = PG_GETARG_TEXT_P(0);
TimeTzADT *time = PG_GETARG_TIMETZADT_P(1);
TimeTzADT *result;
- TimeADT time1;
int tz;
int type,
val;
{
tz = val * 60;
#ifdef HAVE_INT64_TIMESTAMP
- time1 = (time->time - ((time->zone + tz) * INT64CONST(1000000)));
- result->time -= ((result->time / time1) * time1);
- if (result->time < INT64CONST(0))
+ result->time = time->time + ((time->zone - tz) * INT64CONST(1000000));
+ while (result->time < INT64CONST(0))
result->time += INT64CONST(86400000000);
+ while (result->time >= INT64CONST(86400000000))
+ result->time -= INT64CONST(86400000000);
#else
- time1 = (time->time - time->zone + tz);
- TMODULO(result->time, time1, 86400e0);
- if (result->time < 0)
+ result->time = time->time + (time->zone - tz);
+ while (result->time < 0)
result->time += 86400;
+ while (result->time >= 86400)
+ result->time -= 86400;
#endif
result->zone = tz;
result = (TimeTzADT *) palloc(sizeof(TimeTzADT));
#ifdef HAVE_INT64_TIMESTAMP
- result->time = (time->time + ((time->zone - tz) * INT64CONST(1000000)));
+ result->time = time->time + ((time->zone - tz) * INT64CONST(1000000));
while (result->time < INT64CONST(0))
result->time += INT64CONST(86400000000);
while (result->time >= INT64CONST(86400000000))
result->time -= INT64CONST(86400000000);
#else
- result->time = (time->time + (time->zone - tz));
+ result->time = time->time + (time->zone - tz);
while (result->time < 0)
result->time += 86400;
while (result->time >= 86400)
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