Question

Is it possible to define now() as a start value for tztsrange data type introduced in postgresql 9.2? I tried to use this

ALTER TABLE test_table ALTER COLUMN tstz_range SET DEFAULT '[now,infinity]'::tstzrange;

But in such expression now() is evaluated into current time stamp by altering table and default value is despite always the same:

'["2012-09-18 15:00:47.334196+02",infinity]'::tstzrange;

Answer 1

As stated in the documentation you can define a range with the according function:

SELECT tstzrange(now(), 'infinity', '[)');
┌────────────────────────────────────────────┐
│                 tstzrange                  │
├────────────────────────────────────────────┤
│ ["2012-09-18 15:33:50.186351+00",infinity) │
└────────────────────────────────────────────┘

So you can easily create a default value using the function:

CREATE TABLE plop (
  id serial PRIMARY KEY, 
  some_range tstzrange DEFAULT tstzrange(now(), 'infinity', '[)')
);