diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/datetime.sgml | 12 | ||||
| -rw-r--r-- | doc/src/sgml/func.sgml | 22 |
2 files changed, 25 insertions, 9 deletions
diff --git a/doc/src/sgml/datetime.sgml b/doc/src/sgml/datetime.sgml index 7da4d0b7789..71fbf842cca 100644 --- a/doc/src/sgml/datetime.sgml +++ b/doc/src/sgml/datetime.sgml @@ -758,6 +758,18 @@ </para> <para> + The four timezone names <literal>EST5EDT</literal>, + <literal>CST6CDT</literal>, <literal>MST7MDT</literal>, + and <literal>PST8PDT</literal> look like they are POSIX zone + specifications. However, they actually are treated as named time zones + because (for historical reasons) there are files by those names in the + IANA time zone database. The practical implication of this is that + these zone names will produce valid historical USA daylight-savings + transitions, even when a plain POSIX specification would not due to + lack of a suitable <filename>posixrules</filename> file. + </para> + + <para> One should be wary that it is easy to misspell a POSIX-style time zone specification, since there is no check on the reasonableness of the zone abbreviation(s). For example, <literal>SET TIMEZONE TO diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 9d71678029e..b7c450ea29d 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -9131,18 +9131,22 @@ SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS 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. + <type>timestamp with time zone</type> by the indicated number of days, + keeping the time of day the same. Across daylight saving time changes (when the session time zone is 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>. + For example, with the session time zone set + to <literal>America/Denver</literal>: +<screen> +SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '1 day'; +<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 12:00:00-06</computeroutput> +SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '24 hours'; +<lineannotation>Result: </lineannotation><computeroutput>2005-04-03 13:00:00-06</computeroutput> +</screen> + This happens because an hour was skipped due to a change in daylight saving + time at <literal>2005-04-03 02:00:00</literal> in time zone + <literal>America/Denver</literal>. </para> <para> |