CREATE OR REPLACE FUNCTION last_day(date)
RETURNS date AS
$$
SELECT (date_trunc('MONTH', $1) + INTERVAL '1 MONTH - 1 day')::date;
$$ LANGUAGE 'sql'
IMMUTABLE STRICT;
Надеюсь, это поможет.
Ответ 2
create or replace funCtion last_day(fromdt anyelement)
returns date as
$BODY$
SELECT (date_trunc('MONTH', cast(fromdt as date)) + INTERVAL '1 MONTH - 1 day')::date;
$BODY$
LANGUAGE sql VOLATILE
COST 100;
ALTER FUNCTION last_day(anyelement)
OWNER TO postgres;