Calculate next working day in future

Question

Hi,
I hope somebody of you could help me here. I have the requirement to find the next working day 2 days after the visit. I need to join two tables which have an N to N relation.
This is the first source table tbl_cust with customer and visiting day:
customer_id    Name     visit_day       company_id
1                   Tobias    27.08.2011  100
2                   Hans      30.08.2011  100
3                   Lars       27.08.2011   200
4                   Dave      29.08.2011   200The second table tbl_comp_days includes the days where the different companies work:
company_id  company_day    working_day (yes/no)
100             27.08.2011       no
100             28.08.2011       no
100             29.08.2011       yes
100             30.08.2011       yes
100             31.08.2011       yes
100             01.09.2011       yes
200             27.08.2011       yes
200             28.08.2011       yes
200             29.08.2011       no
200             30.08.2011       yes
200             31.08.2011       yes
200             01.09.2011       yesNow I want to calculate the second next work of the company joined with the customer visit_day
Means: tbl_cust.visit_day + 2
when tbl_comp_days.working_day is yes
if tbl_cust.visit_day is not a working day find the next possible working day + 2 working days
Output example:
customer_id    Name     visit_day       visit_day_plus_2
1                   Tobias    27.08.2011  31.08.2011
2                   Hans      30.08.2011  01.09.2011
3                   Lars       27.08.2011   30.08.2011
4                   Dave       29.08.2011   01.09.2011Thanks for your help
Tobias

Answer 1

Hi, Tobias,
Here's one way:
WITH     got_r_num    AS
     SELECT     c.customer_id, c.name, c.visit_day, d.company_day  AS visit_day_plus_2
     ,     ROW_NUMBER () OVER ( PARTITION BY  c.customer_id
                               ORDER BY          d.company_day
                       )         AS r_num
     FROM    tbl_cust       c
     JOIN     tbl_comp_days  d  ON   c.company_id  = d.company_id
                             AND  c.visit_day   < d.company_day
                      AND  c.visit_day   >= d.company_day + 10     -- See note
     WHERE   d.working_day       = 'yes'
SELECT     customer_id, name, visit_day, visit_day_plus_2
FROM     got_r_num
WHERE     r_num     = 2
;If you'd post CREATE TABLE and INSERT statements for the sample data, then I could test it.
The last join condition ( c.visit_day >= d.company_day + 10) isn't strictly necessary. Depending on the size of the company_day table, it may make execution faster, by limiting the join to days soon after visit_day, rather than any time after visit_day. As I wrote it, it assumes that there will always be at least 2 working days in any period of 10 consecutive days. (In my company, there are always at least 2 working days in a period of 5 consecutive days.) You cam change the "magic number" 10 to anything else, or you can omit that condition altogether.
Edited by: Frank Kulash on Aug 23, 2011 10:49 AM
Added note.