I’m having some trouble with
time with time zone equalities in Postgres.
timestamp with time zone equality works how I would expect it to, where if the times are the same after normalizing the timezones, it should be true:
postgres=# select '2013-06-27 12:00:00 -0800'::timestamp with time zone = '2013-06-27 14:00:00 -0600'::timestamp with time zone; ?column? ---------- t
However, the same does not seem to apply to
time with time zone:
postgres=# select '12:00:00 -0800'::time with time zone = '14:00:00 -0600'::time with time zone; ?column? ---------- f
Yet inequalities work how I would expect them to:
postgres=# select '12:00:00 -0800'::time with time zone < '14:01:00 -0600'::time with time zone; ?column? ---------- t postgres=# select '12:00:00 -0800'::time with time zone > '13:59:00 -0600'::time with time zone; ?column? ---------- t
Is there something I’m misunderstanding about
time with time zone? How can I evaluate for equality in a way that handles time zones the same way
timestamp with time zone equality does?
Here are two ways to evaluate
SELECT a, b, a = b AS plain_equality , '2000-1-1'::date + a = '2000-1-1'::date + b AS ts_equality , a AT TIME ZONE 'UTC', b AT TIME ZONE 'UTC' AS timetz_equality FROM ( SELECT '12:00:00 -0800'::timetz AS a , '14:00:00 -0600'::timetz AS b ) sub;
The first by adding it to a
The second by using the
AT TIME ZONE construct.
But rather don’t use
time with time zone at all.
Postgres supports the type only because it is in the SQL standard. It is broken by design (cannot consider DST!) and its use is discouraged.
Quoting the manual here:
time with time zoneis defined by the SQL standard, but the definition exhibits properties which lead to questionable usefulness. In most cases, a combination of
timestamp without time zone, and
timestamp with time zoneshould provide a complete range of date/time functionality required by any application.