Casting with intervals

You can use CAST to convert strings to intervals, and vice versa.

String to interval

You cast a string to an interval as follows:

CAST( [ INTERVAL[(p)] ] [-] ] interval-literal AS INTERVAL[(p)] interval-qualifier )

For example:

=> SELECT CAST('3700 sec' AS INTERVAL);
 ?column?
----------
 01:01:40

You can cast intervals within day-time or the year-month subtypes but not between them:

=> SELECT CAST(INTERVAL '4440' MINUTE as INTERVAL);
  ?column?
----------
 3 days 2 hours
=> SELECT CAST(INTERVAL -'01:15' as INTERVAL MINUTE);
 ?column?
----------
 -75 mins

Interval to string

You cast an interval to a string as follows:

CAST( (SELECT interval ) AS VARCHAR[(n)] )

For example:

=> SELECT CONCAT(
  'Tomorrow at this time: ',
  CAST((SELECT INTERVAL '24 hours') + CURRENT_TIMESTAMP(0) AS VARCHAR));
                    CONCAT
-----------------------------------------------
 Tomorrow at this time: 2016-08-17 08:41:23-04
(1 row)