<!--
-$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.273 2005/07/29 14:46:56 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.274 2005/07/30 14:52:04 momjian Exp $
PostgreSQL documentation
-->
such pair.
</para>
+ <para>
+ When adding an <type>interval</type> value to (or subtracting an
+ <type>interval</type> value from) a <type>timestamp with time zone</type>
+ value, the days component advances (or decrements) the date of the
+ <type>timestamp with time zone<type> by the indicated number of days.
+ Across daylight saving time changes (with the session tiem zone set to a
+ time zone that recognizes DST), this means <literal>interval '1 day'</literal>
+ does not necessarily equal <literal>interval '24 hours'</literal>.
+ For example, with the session time zone set to <literal>CST7CDT</literal>
+ <literal>timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' </literal>
+ will produce <literal>timestamp with time zone '2005-04-03 12:00-06'</literal>,
+ while adding <literal>interval '24 hours'</literal> to the same initial
+ <type>timestamp with time zone</type> produces
+ <literal>timestamp with time zone '2005-04-03 13:00-06'</literal>, as there is
+ a change in daylight saving time at <literal>2005-04-03 02:00</literal> in time zone
+ <literal>CST7CDT</literal>.
+ </para>
+
<table id="operators-datetime-table">
<title>Date/Time Operators</title>
t
(1 row)
+-- timestamp with time zone, interval arithmetic around DST change
+SET TIME ZONE 'CST7CDT';
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
+ Apr 3, 12:00
+------------------------------
+ Sun Apr 03 12:00:00 2005 CDT
+(1 row)
+
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '24 hours' as "Apr 3, 13:00";
+ Apr 3, 13:00
+------------------------------
+ Sun Apr 03 13:00:00 2005 CDT
+(1 row)
+
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '1 day' as "Apr 2, 12:00";
+ Apr 2, 12:00
+------------------------------
+ Sat Apr 02 12:00:00 2005 CST
+(1 row)
+
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '24 hours' as "Apr 2, 11:00";
+ Apr 2, 11:00
+------------------------------
+ Sat Apr 02 11:00:00 2005 CST
+(1 row)
+
+RESET TIME ZONE;
SELECT timestamptz(date '1994-01-01', time '11:00') AS "Jan_01_1994_10am";
Jan_01_1994_10am
------------------------------
@ 4541 years 4 mons 4 days 17 mins 31 secs
(1 row)
+-- test justify_hours() and justify_days()
+SELECT justify_hours(interval '6 months 3 days 52 hours 3 minutes 2 seconds') as "6 mons 5 days 4 hours 3 mins 2 seconds";
+ 6 mons 5 days 4 hours 3 mins 2 seconds
+----------------------------------------
+ @ 6 mons 5 days 4 hours 3 mins 2 secs
+(1 row)
+
+SELECT justify_days(interval '6 months 36 days 5 hours 4 minutes 3 seconds') as "7 mons 6 days 5 hours 4 mins 3 seconds";
+ 7 mons 6 days 5 hours 4 mins 3 seconds
+----------------------------------------
+ @ 7 mons 6 days 5 hours 4 mins 3 secs
+(1 row)
+
SELECT (timestamp with time zone 'tomorrow' = (timestamp with time zone 'yesterday' + interval '2 days')) as "True";
SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
+-- timestamp with time zone, interval arithmetic around DST change
+SET TIME ZONE 'CST7CDT';
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '1 day' as "Apr 3, 12:00";
+SELECT timestamp with time zone '2005-04-02 12:00-07' + interval '24 hours' as "Apr 3, 13:00";
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '1 day' as "Apr 2, 12:00";
+SELECT timestamp with time zone '2005-04-03 12:00-06' - interval '24 hours' as "Apr 2, 11:00";
+RESET TIME ZONE;
+
+
SELECT timestamptz(date '1994-01-01', time '11:00') AS "Jan_01_1994_10am";
SELECT timestamptz(date '1994-01-01', time '10:00') AS "Jan_01_1994_9am";
SELECT timestamptz(date '1994-01-01', time with time zone '11:00-8') AS "Jan_01_1994_11am";
-- test long interval input
select '4 millenniums 5 centuries 4 decades 1 year 4 months 4 days 17 minutes 31 seconds'::interval;
+
+
+-- test justify_hours() and justify_days()
+
+SELECT justify_hours(interval '6 months 3 days 52 hours 3 minutes 2 seconds') as "6 mons 5 days 4 hours 3 mins 2 seconds";
+SELECT justify_days(interval '6 months 36 days 5 hours 4 minutes 3 seconds') as "7 mons 6 days 5 hours 4 mins 3 seconds";
+