create table tableA (from_date date, to_date date)

create table tableB (id integer, valid_from date, valid_to date)

insert into tableA values (date'2015-11-10',date'9999-12-31')

insert into tableB values (1,date'2015-11-10',date'2015-12-31')

insert into tableB values (2,date'2016-11-11',date'2016-12-31')

with dates as ( 
  select distinct dte from ( 
    select from_date, to_date+case when to_date<date'9999-12-31' then 1 else 0 end to_date from tableA 
    union all 
    select valid_from as from_date, valid_to+case when valid_to<date'9999-12-31' then 1 else 0 end as to_date from tableB 
  ) 
  unpivot(dte for col in(from_date, to_date)) 
) 
select row_number() over (order by from_date) as id, from_date, to_date-case when to_date<date'9999-12-31' then 1 else 0 end as to_date from ( 
  select distinct dte from_date, 
  lead(dte) over(order by dte) to_date 
  from dates a 
  left join tableA b on a.dte between b.from_date and b.to_date 
  left join (select valid_from as from_date, valid_to as to_date from tableB) c on a.dte between c.from_date and c.to_date 
) 
where from_date is not null and to_date is not null 
order by 1,2