Convert Timestamp to Seconds of Day (ignoring the date part)

ts_to_seconds_of_day.sql

drop function if exists transformation_utils.ts_to_seconds_of_day (p_timestamp timestamp);
create or replace function transformation_utils.ts_to_seconds_of_day (p_timestamp timestamp)
  returns integer AS
$body$ 
declare 
    hs integer;
    ms integer;
    s  integer;
begin
    select (extract (hour    from p_timestamp::time) * 60 * 60) into hs; 
    select (extract (minutes from p_timestamp::time) * 60     ) into ms;
    select (extract (seconds from p_timestamp::time)		  ) into s;
    select (hs + ms + s) into s;
    return s;
end;
$body$
  language 'plpgsql';