diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5e95325250..9f2b1d4923 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -7889,10 +7889,11 @@ SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
- The AT TIME ZONE construct allows conversions
- of time stamps to different time zones. shows its
- variants.
+ The AT TIME ZONE converts time
+ stamp without time zone to/from
+ time stamp with time zone, and
+ time values to different time zones. shows its variants.
@@ -7937,24 +7938,33 @@ SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
In these expressions, the desired time zone zone> can be
- specified either as a text string (e.g., 'PST')
+ specified either as a text string (e.g., 'America/Los_Angeles')
or as an interval (e.g., INTERVAL '-08:00').
In the text case, a time zone name can be specified in any of the ways
described in .
- Examples (assuming the local time zone is PST8PDT>):
+ Examples (assuming the local time zone is America/Los_Angeles):
-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';
Result: 2001-02-16 19:38:40-08
-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';
Result: 2001-02-16 18:38:40
+
+SELECT TIMESTAMP '2001-02-16 20:38:40-05' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago';
+Result: 2001-02-16 05:38:40
- 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 TimeZone
+ 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
+ TimeZone setting. The third example converts
+ Tokyo time to Chicago time. Converting time
+ values to other time zones uses the currently active time zone rules
+ since no date is supplied.