create table bd (id int primary key, bday date);

insert into bd values (1, '20180102'),(2, '20180104'),(3, '20180106'),(4, '20180108'),(5, '20180110'),(6, '20180112');

select * from bd;

-- adding four bussines days to 03/01/2018 select max(bday) as the_day from ( select * from bd where bday > '20180103' limit 4 ) bd;

select bday from (select bday, row_number() over (order by bday) rn from bd where bday > '20180103') bd where rn = 4;

create or replace function add_bussines_day(bday date, num_days int) returns date as $fbd$ select max(bday) as the_day from (select * from bd where bday > $1 limit $2 ) bd; $fbd$ language sql;

select add_bussines_day('20180103', 4);