30 Business Days Back

Question

Hi All,
I need to find the calendar date 30 business days back from SYSDATE:
Formula: Calendar Date = SYSDATE - "30 business days"
I have a table contains:
cal_dt,bus_day,holiday
7/1/10,1,NULL
7/2/10,1,NULL
7/3/10,0,NULL
7/4/10,0,NULL
7/5/10,0,'Y'
7/6/10,1,NULL
For the life of me, I can't figure it out how to write the SQL? Please help.
Using Oracle 10g.
Thanks,
Mary

Answer 1

The first query gives you: Today's date - 30 'BUSINESS' days
select cal_dt
from
select cal_dt, bus_day, holiday,
row_number() over (order by cal_dt desc) rn
from calendar
where cal_dt <= TRUNC(SYSDATE)
and bus_day = 1
and holiday is NULL
where rn = 31;
The second query gives you: Last 'BUSINESS' day preceding (Today's date - 30 'CALENDER' days)
Select cal_dt
from (
select cal_dt, bus_day, holiday,
row_number() over (order by cal_dt desc) rn
from calendar
where cal_dt <= TRUNC(SYSDATE-30)
and bus_day = 1
and holiday is NULL
where rn = 1;
Or, you may try a simple alternative to my first query:
select cal_dt
from
select cal_dt, ROWNUM rn
from
select cal_dt, bus_day, holiday
from calendar
where cal_dt <= TRUNC(SYSDATE)
and bus_day = 1
and holiday is NULL
order by cal_dt
where rn = 31;
You may try to run these queries step by step to check what is happening and what suits to your needs.