Seconds since midnight?

seconds_since_midnight.sql

-- Note that this doesn't work:
-- SELECT DATEDIFF(second, DATE(NOW()), NOW());
-- => 
-- ERROR:  function pg_catalog.date_diff("unknown", date, timestamp with time zone) does not exist
-- HINT:  No function matches the given name and argument types. You may need to add explicit type casts.

-- This does work:
SELECT DATEDIFF(second, DATE(NOW()), SPLIT_PART(NOW(), '.', 1)::timestamp);

select extract(epoch from now() - current_date);