插入时区夏令时的时间

Question

I would like to insert time data type in postgresql that includes the timezone and is aware of daylight savings time. This is what I have done:

CREATE TABLE mytable(
    ...
    start_time time(0) with time zone,
    end_time time(0) with time zone
)

INSERT INTO mytable(start_time, end_time)
VALUES(TIME '08:00:00 MST7MDT', TIME '18:00:00 MST7MDT')

I get the following error:

invalid input syntax for type time: "08:00:00 MST7MDT"

It works if I use 'MST' instead of 'MST7MDT', but I need it to be aware of DST. I also tried using 'America/Edmonton' as the timezone, but I got the same error.

What is the proper way to insert a time value (not timestamp) with timezone and DST?

EDIT: I would actually like to use the 'America/Edmonton' syntax

Answer 1

The proper way is not to use time with time zone (note the space between time and zone ) at all, since it is broken by design. It is in the SQL standard, so Postgres supports the type - but advises not to use it. More in this related answer:

• Accounting for DST in Postgres, when selecting scheduled items

Since you are having problems with DST , timetz (short name) is a particularly bad choice. It is ill-equipped to deal with DST. It's impossible to tell whether 8:00:00 is in winter or summer time.

Use timestamp with time zone ( timstamptz ) instead. You can always discard the date part. Simply use start_time::time to get the local time from a timestamptz . Or use AT TIME ZONE to transpose to your time zone.

Generally, to take DST into account automatically , use a time zone name instead of a time zone abbreviation. More explanation in this related question & answer:

• Time zone names with identical properties yield different result when applied to timestamp

In your particular case, you could probably use America/Los_Angeles (example with timestamptz ):

INSERT INTO mytable(start_time, end_time)
VALUES
   ('1970-01-01 08:00:00 America/Los_Angeles'
  , '1970-01-01 18:00:00 America/Los_Angeles')

I found this by checking:

SELECT * FROM pg_timezone_names 
WHERE  utc_offset = '-07:00'
AND    is_dst;

Basics about time zone handling:

• Ignoring time zones altogether in Rails and PostgreSQL

Answer 2

How about this?

INSERT INTO mytable(start_time, end_time)
VALUES('08:00:00'::time at time zone 'MST7MDT', '18:00:00'::time at time zone 'MST7MDT')