Bharanee Rathna <deepfryed(at)gmail(dot)com> writes:
> To be more specific, I expected the output of both these queries to be the
> same.
> # select '2017-12-01 11:00:00 +11:00'::timestamp with time zone at time
> zone '+11:00';
> # select '2017-12-01 11:00:00 +11:00'::timestamp with time zone at time
> zone 'Australia/Melbourne';
The +11 in your timestamp input value is per ISO convention, but the
argument of AT TIME ZONE is a zone name, so it follows the POSIX
convention if it's numeric.
regards, tom lane