How to extract consistent year from timestamptz

Question

I'm trying to use the Postgres function extract() to get the year from a timestamptz column, but get unexpected results. I expected that it would use UTC, but appears to use whatever the local timezone of the system is (EST in my case). How do I get the extract function to return UTC regardless of what the timezone of the timestamp or the system is?

Example 1:

testdb=# create table foo ( t timestamptz check( extract(year from t)::int = 2013) );

testdb=# \d foo
              Table "public.foo"
 Column |           Type           | Modifiers
--------+--------------------------+-----------
 t      | timestamp with time zone |
Check constraints:
    "foo_t_check" CHECK (date_part('year'::text, t)::integer = 2013)

testdb=# insert into foo values ('2013-01-01 01:49:05.048+00');
ERROR:  new row for relation "foo" violates check constraint "foo_t_check"
DETAIL:  Failing row contains (2012-12-31 20:49:05.048-05).

Example 2:

testdb=# SELECT EXTRACT(year FROM '01-01-1970 00:00:00 UTC+01'::timestamp with time zone);
 date_part
-----------
      1969
(1 row)

Answer 1

Use at time zone

create table foo (
    t timestamptz
    check (extract(year from t at time zone 'UTC') = 2013)
);

select extract(year from
    '01-01-1970 00:00:00 utc+01'::timestamp with time zone at time zone 'utc'
    );
 date_part 
-----------
      1970