PostgreSQL interval error

Question

I run a query like this:

SELECT (SELECT expire_date FROM "License" WHERE license_id = 10)
      - interval '1 mon 133 days 22:19:49.191748'

And everything is well.
But when I try this:

SELECT (SELECT expire_date FROM "License" WHERE license_id = 10)
      - interval ((SELECT expire_date-now() FROM "License" WHERE license_id = 10)
                 + interval '1 months')

I get an error:

ERROR:  syntax error at or near "("
LINE 1: ...FROM "License" WHERE license_id = 10) - interval ((SELECT ex...
                                                             ^

Please help, thanks.

Answer 1

My understanding is that Postgres allows the type 'string' syntax for specifying the type for simple literal constants. For anything else you have to use ...::type or CAST ( ... AS type ).