--
-- Тестовые данные:
with t (code, date_low, date_up, sum) as (
  values (1, date '2015-01-01', date '2020-12-31', 100)
       , (1, date '2021-01-01', date '2025-12-31', 150)
)
--
-- Основной запрос
select distinct code
      , min(date_low) over(partition by code) as min_date_low
      , max(date_up) over(partition by code) as max_date_up
      , first_value(sum) over(partition by code order by date_up desc) as x_sum
  from t

--
-- Тестовые данные:
with t (code, date_low, date_up, sum) as (
  values (1, date '2015-01-01', date '2020-12-31', 100)
       , (1, date '2021-01-01', date '2025-12-31', 150)
)
--
-- Основной запрос:
select code
     , min(date_low) as min_date_low
     , max(date_up) as max_date_up
     , substring(max(to_char(date_up, 'yyyymmddhh24miss')||sum::text) from 15)::int as x_sum
  from t
 group by code