Calculate closest working day in Postgres

Question

I need to schedule some items in a postgres query based on a requested delivery date for an order. So for example, the order has a requested delivery on a Monday (20120319

Answer 1

To have the previous work day:

select max(s.a) as work_day
from (
    select s.a::date
    from generate_series('2012-01-02'::date, '2050-12-31', '1 day') s(a)
    where extract(dow from s.a) between 1 and 5
    except
    select holiday_date
    from holiday_table
    ) s
where s.a < '2012-03-19'
;

If you want the next work day just invert the query.