How can I find consecutive active weeks in SQL? - sql

Question

What I would like to do is find the number of consecutive weeks that someone is active on Sundays and assign them a value. They have to participate in at least 2 races a day to be counted as active for the week.
If they are active for 2 consecutive weeks I would like to assign a value of 100, 3 consecutive weeks a value of 200, 4 consecutive weeks a value of 300, and continuing up to 9 consecutive weeks.
My difficulty is not determining consecutive weeks, but breaks in between consecutive dates. Suppose the following dataset:
CustomerID RaceDate Races
1 2/2/2014 2
1 2/9/2014 5
1 2/16/2014 3
1 2/23/2014 3
1 3/2/2014 4
1 3/9/2014 3
1 3/16/2014 3
2 2/2/2014 2
2 2/9/2014 3
2 3/2/2014 2
2 3/9/2014 4
2 3/16/2014 3
CustomerID 1 would have 7 consecutive weeks for a value of 600.
The hard part for me is CustomerID 2. They would have 2 consecutive weeks AND 3 consecutive weeks. So their total value would be 100 + 200 = 300.
I would like to be able to do this with any different combination of consecutive weeks.
Any help please?
EDIT: I am using SQL Server 2008 R2.

Answer 1

When looking for sequential values, there is a simple observation that helps. If you subtract a sequence from the dates then the value is a constant. You can use this as a grouping mechanism
select CustomerId, min(RaceDate) as seqStart, max(RaceDate) as seqEnd,
count(*) as NumDaysRaced
from (select t.*,
dateadd(week, - row_number() over (partition by customerID, RaceDate),
RaceDate) as grp
from table t
where races >= 2
) t
group by CustomerId, grp;
You can then use this to get your final "points":
select CustomerId,
sum(case when NumDaysRaced > 1 then (NumDaysRaced - 1) * 100 else 0 end) as Points
from (select CustomerId, min(RaceDate) as seqStart, max(RaceDate) as seqEnd,
count(*) as NumDaysRaced
from (select t.*,
dateadd(week, - row_number() over (partition by customerID, RaceDate),
RaceDate) as grp
from table t
where races >= 2
) t
group by CustomerId, grp
) c
group by CustomerId;