How to add number of business days to given date

Question

I\'m looking for a function which adds number of business days to given date.

Holidays table

create table pyha (pyha date primary key) ;
insert into          


        

Answer 1

Here's a solution if you don't want to rely on generate_series. It's a fairly straight forward algorithm that allows you to specify your own business day definition via an array. The default business days (mo-fr) would be defined like this array[0,1,1,1,1,1,0]. Since it doesn't use generate_series it presumably is much faster especially for larger intervals.

It doesn't consider the holiday table case, but will hopefully be a helpful pointer nonetheless.

create or replace function add_business_days(start timestamp with time zone, business_days int[], add_days int)
  returns timestamp with time zone as $$
  declare
    days_left int := add_days;
    num_bds int := (select sum(x.val) from ( select unnest(business_days) val ) as x);
    add_real_days int := 0;
    start_dow int := extract(dow from start);
  begin
    -- if all weekdays are false just ignore the logic below
    if num_bds = 0 then
      return start + make_interval(days := add_days);
    end if;

    -- if the start day is no business day, go forward until we hit one
    while business_days[((start_dow + add_real_days) % 7) + 1] = 0 loop
      add_real_days := add_real_days + 1;
    end loop;

    -- jump to the final week
    add_real_days := add_real_days + (days_left / num_bds)::int * 7;
    days_left := days_left % num_bds;

    -- go ahead with the remaining days until we hit a business day
    while days_left > 0 or business_days[((start_dow + add_real_days) % 7) + 1] = 0 loop
      add_real_days := add_real_days + 1;
      days_left := days_left - business_days[((start_dow + add_real_days) % 7) + 1];
    end loop;
    return start + make_interval(days := add_real_days);
  end;
$$
language plpgsql immutable;

You can use the function like this:

select add_business_days(now(), array[0,1,1,1,1,0], 4);