redshift datediff not working when current_timestamp is used but working when getdate() function is used

Question

I am querying a timestamp column with datediff from current_timestamp. But it gives error.

DATEDIFF(minute, timestamp_field ,current_timestamp::TIMESTAMP) 
or 
DATEDIFF(minute, timestamp_field ,current_timestamp)
DataType of timestamp_field is "TIMESTAMP DEFAULT '2016-03-29 20:33:33.404256'::timestamp without time zone"

OutPut:

ERROR: Specified types or functions (one per INFO message) not supported on Redshift tables.

Warnings: Function ""timestamp"(timestamp with time zone)" not supported. Function "timestamptz(timestamp with time zone,integer)" not supported. Function "timestamptz(text)" not supported.

But following query is working if I use getdate() function

DATEDIFF(minute, timestamp_field ,getdate()::TIMESTAMP)

Answer 1

I just simply casted the timestamp with timezone to timestamp and it was working.

example:

select datediff(min, CURRENT_TIMESTAMP::timestamp, CURRENT_TIMESTAMP::timestamp);