Query for an empty time range in Postgres

Question

I recently discovered that a time range can be empty which appears to be different vs a null field.

db=# select tstzrange(now(), now());
 tstzrange
-----------
 empty
(1 row)

db=# select tstzrange(now(), now()) is null;
 ?column?
----------
 f
(1 row)

How can I match an empty field for a query?

Answer 1

Compare it with a string 'empty'

select tstzrange(now(), now()) = 'empty' as out

which produces:

 out
-----
 t

While for a non-empty result with query like:

select tstzrange(now(), now() + interval '1d') = 'empty' as out

it consistently produces:

 out
-----
 f

In fact implicit conversion of 'empty'::tstzrange takes place.

Read more on the matter in documentation

Answer 2

use isempty()

select isempty(tstzrange(now(), now())); -- true
select isempty(tstzrange(now(), now() + interval '1d')); -- false