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| -rw-r--r-- | doc/src/sgml/func.sgml | 32 |
1 files changed, 21 insertions, 11 deletions
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index bb794e044f4..df847c0df6c 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -8082,10 +8082,11 @@ SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40'); </indexterm> <para> - The <literal>AT TIME ZONE</literal> construct allows conversions - of time stamps to different time zones. <xref - linkend="functions-datetime-zoneconvert-table"/> shows its - variants. + The <literal>AT TIME ZONE</literal> converts time + stamp <emphasis>without time zone</emphasis> to/from + time stamp <emphasis>with time zone</emphasis>, and + <emphasis>time</emphasis> values to different time zones. <xref + linkend="functions-datetime-zoneconvert-table"/> shows its variants. </para> <table id="functions-datetime-zoneconvert-table"> @@ -8130,24 +8131,33 @@ SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40'); <para> In these expressions, the desired time zone <replaceable>zone</replaceable> can be - specified either as a text string (e.g., <literal>'PST'</literal>) + specified either as a text string (e.g., <literal>'America/Los_Angeles'</literal>) or as an interval (e.g., <literal>INTERVAL '-08:00'</literal>). In the text case, a time zone name can be specified in any of the ways described in <xref linkend="datatype-timezones"/>. </para> <para> - Examples (assuming the local time zone is <literal>PST8PDT</literal>): + Examples (assuming the local time zone is <literal>America/Los_Angeles</literal>): <screen> -SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST'; +SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'America/Denver'; <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'; +SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/Denver'; <lineannotation>Result: </lineannotation><computeroutput>2001-02-16 18:38:40</computeroutput> + +SELECT TIMESTAMP '2001-02-16 20:38:40-05' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago'; +<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 05:38:40</computeroutput> </screen> - The first example takes a time stamp without time zone and interprets it as MST time - (UTC-7), which is then converted to PST (UTC-8) for display. The second example takes - a time stamp specified in EST (UTC-5) and converts it to local time in MST (UTC-7). + The first example adds a time zone to a value that lacks it, and + displays the value using the current <varname>TimeZone</varname> + setting. The second example shifts the time stamp with time zone value + to the specified time zone, and returns the value without a time zone. + This allows storage and display of values different from the current + <varname>TimeZone</varname> setting. The third example converts + Tokyo time to Chicago time. Converting <emphasis>time</emphasis> + values to other time zones uses the currently active time zone rules + since no date is supplied. </para> <para> |