How to extract hour from query in postgres

Question

I have timestamp in my table and i want to extract only hour from it. I search and find a extract function but unable to use as a query. Do i need to convert first timestamp

Answer 1

The word timezone is redundant (read: wrong). You just need to give the column's name. E.g.:

db=> select extract(hour from observationtime) from smartvakt_device_report;

 date_part 
-----------
        19
(1 row)

Answer 2

The following should work

select extract(hour from observationtime) from smartvakt_device_report

Answer 3

SELECT to_char(now(), 'HH24:MI:SS')  hour_minute_second