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SQL server query solution

Posted on 2004-10-08
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Last Modified: 2012-05-05
Say I have a table Table1 with 3 cols
Table1
(
    consultant_id  int,
    date_value     datetime,
    available_ind  char(1)
)
and if I am looking for max number of consecutive days that a consultant is available within a date range, is there any way to do so using a SELECT i.e. not having to cursor through.

sample data (ordered by consultant_id, date_value)

consultant_id    date_value    available_ind
1                     1/1/04           Y
1                     1/15/04         Y
1                     2/2/04           Y
1                     2/3/04           N
1                     2/11/04         Y
1                     3/1/04           Y
1                     3/11/04         N
1                     3/21/04         Y
1                     3/22/04         Y

so the result should be that the consultant is available for max of 3 consecutive days.
0
Comment
Question by:nishaj
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8 Comments
 
LVL 12

Expert Comment

by:monosodiumg
ID: 12262261

select consultant_id, max(datediff(d, date_value1, date_value2))
  from data d1 inner join data d2 on d1.consultant_id = d2.consultant_id and d1.date_value <= d2.date_value
  where not exists(select 1 from data d3 where d3.consultant_id = d1.consultant_id and d3.date_value between d1.date_value and d2.date_value and d.available_ind = 'N')
0
 
LVL 12

Expert Comment

by:monosodiumg
ID: 12262275
forgot the  group by clause:

select d1.consultant_id, max(datediff(d, d1.date_value, d2.date_value))
  from data d1 inner join data d2 on d1.consultant_id = d2.consultant_id and d1.date_value <= d2.date_value
  where not exists(select 1 from data d3 where d3.consultant_id = d1.consultant_id and d3.date_value between d1.date_value and d2.date_value and d.available_ind = 'N')
group by consultant_id
0
 

Author Comment

by:nishaj
ID: 12262518
did not work.
sample data
      1      1/1/2004      Y
      1      1/2/2004      Y
      1      1/3/2004      N
      1      1/4/2004      Y
      1      1/5/2004      Y
      1      1/6/2004      Y
      1      1/7/2004      Y
      1      1/8/2004      N
      2      1/1/2004      Y
      2      1/2/2004      Y
      2      1/3/2004      N
corrected the alias in the last row to be d3? is that what was intended.

results
1              3
2              1
0
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LVL 12

Accepted Solution

by:
monosodiumg earned 750 total points
ID: 12262702
So we are exactly one day short?

select d1.consultant_id, max(datediff(d, d1.date_value, d2.date_value)) + 1
  from data d1 inner join data d2 on d1.consultant_id = d2.consultant_id and d1.date_value <= d2.date_value
  where not exists(select 1 from data d3 where d3.consultant_id = d1.consultant_id and d3.date_value between d1.date_value and d2.date_value and d3.available_ind = 'N')
group by consultant_id

>corrected the alias in the last row to be d3? is that what was intended.
Yes.
0
 

Author Comment

by:nishaj
ID: 12262726
Another possible way..
SELECT
      cons_key,
      max (count_diff)
FROM
      (
            SELECT
                  c1.consultant_key cons_key,
                  (DATEDIFF(DAY,c1.date_value, min (c2.date_value))) count_diff
            FROM
                  Cal1 c1,
                  cal1 c2
            WHERE
                  c1.avail_ind = "Y"
            AND
                  c2.date_value > c1.date_value
            AND
                  c2.avail_ind = "N"      
            AND
                  c1.consultant_key = c2.consultant_key
            group by
                  c1.consultant_key,
                  c1.date_value
      ) x
group by cons_key
0
 

Author Comment

by:nishaj
ID: 12262750
Thanks monosodiumg.
0
 
LVL 12

Expert Comment

by:monosodiumg
ID: 12265788
I think you need to check your alternative solution on a set where the longest available period is on after which there are no N days e.g.:
     1     1/1/2004     Y
     1     1/2/2004     Y
     1     1/3/2004     N
     1     1/4/2004     Y
     1     1/5/2004     Y
     1     1/6/2004     Y
     1     1/7/2004     Y
     2     1/1/2004     Y
     2     1/2/2004     Y

On this set your inner select will fail to pick up the period from 1/4 to 1/7 for consultant 1 because of the  c2.avail_ind = "N"  clause.

I've realised I could add a clause to mine to make it slightly faster:
select d1.consultant_id, max(datediff(d, d1.date_value, d2.date_value)) + 1
  from data d1 inner join data d2 on d1.consultant_id = d2.consultant_id and d1.date_value <= d2.date_value
  where not exists(select 1 from data d3 where d3.consultant_id = d1.consultant_id and d3.date_value between d1.date_value and d2.date_value and d3.available_ind = 'N')
where d1.available_ind = 'Y' and d2.available_ind = 'Y'
group by consultant_id
0
 

Author Comment

by:nishaj
ID: 12276158
Yes you are right, monosodiummg, thanks for pointing that out.
0

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