Running aggregate column among pairs of varying order - sql-server-2008

Question

If I have such data:
Id, Team1, Team2, Score1, Score2
--------------------------------
1, Aaa, Bbb, 10, 8
2, Aaa, Bbb, 6, 8
3, Aaa, Bbb, 6, 5
4, Bbb, Aaa, 9, 7
5, Aaa, Ccc, 12, 6
How I can get a column with difference between scores among teams (running aggregate)?
Example:
Id, Team1, Team2, Score1, Score2 Abs(DIFF)
-------------------------------- ---------
1, Aaa, Bbb, 10, 8 2
2, Aaa, Bbb, 6, 8 0
3, Aaa, Bbb, 6, 5 1
4, Bbb, Aaa, 7, 9 3
5, Aaa, Ccc, 12, 6 6
Please notice two things in the above example:
Order of teams among pair may vary (like in between row 1 and 4)
Table may contain many team pairs
Is it possible to get this DIFF column without using cursor or an update trick?
Query has to run on SQL Server 2008.
I rarely do DB work so simple explanations are welcome.
UPDATE Additional explanation:
In the first row the DIFF is 2 because team Aaa won by two points
In the second row the DIFF is 0 because this time team Bbb won by two points
In the third row the DIFF is 1 because team Aaa won again (by one point)
In the forth row the DIFF is 3 because team Aaa won again (by two points)
So by looking at the DIFF value, one should be able to answer a question like "what is the current difference in score between teams?".

Answer 1

Going with your second sample data (row 3 is tied in first sample, and row 4's score switch sides):
declare #t table (Id int not null,Team1 char(3) not null,Team2 char(3) not null,
Score1 int not null,Score2 int not null)
insert into #t(Id, Team1, Team2, Score1, Score2) values
(1, 'Aaa', 'Bbb', 10, 8),
(2, 'Aaa', 'Bbb', 6, 8),
(3, 'Aaa', 'Bbb', 6, 5),
(4, 'Bbb', 'Aaa', 7, 9),
(5, 'Aaa', 'Ccc', 12, 6)
;With NormTeams as (
select Id,
CASE WHEN Team1 < Team2 THEN Team1 ELSE Team2 END as Team1,
CASE WHEN Team1 < Team2 THEN Team2 ELSE Team1 END as Team2,
CASE WHEN Team1 < Team2 THEN Score1 ELSE Score2 END as Score1,
CASE WHEN Team1 < Team2 THEN Score2 ELSE Score1 END as Score2,
(Score1 - Score2) * CASE WHEN Team1 < Team2 THEN 1 ELSE -1 END as ScoreDiff
from #t
), MatchingTeams as (
select *,ROW_NUMBER() OVER (PARTITION By Team1,Team2 ORDER BY ID) as rn
from NormTeams
)
select *,
(SELECT SUM(ScoreDiff) from MatchingTeams mt2 where
mt2.Team1 = mt1.Team1 and mt2.Team2 = mt1.Team2 and
mt2.rn <= mt1.rn) as RunningDiff
from MatchingTeams mt1
There's unfortunately nothing much that can make it neater until you can use the 2012 windowed aggregates.
Result:
Id Team1 Team2 Score1 Score2 ScoreDiff rn RunningDiff
----------- ----- ----- ----------- ----------- ----------- -------------------- -----------
1 Aaa Bbb 10 8 2 1 2
2 Aaa Bbb 6 8 -2 2 0
3 Aaa Bbb 6 5 1 3 1
4 Aaa Bbb 9 7 2 4 3
5 Aaa Ccc 12 6 6 1 6
You'll notice that the first thing I do is the obvious - switch teams and scores around, if necessary, so that the rest of the query can assume that they do appear in a consistent order.

Answer 2

try this:
;WITH CTE as
(
select id,Team1,Team2,Score1,Score2,0 as RS1,0 as RS2,ABS(Score1-Score2) as DIFF from Table1 where id=1
UNION ALL
select t1.id,t1.Team1,t1.Team2,t1.Score1,t1.Score2,c.score1+t1.Score1,c.score2+t1.Score2,ABS((c.score1+t1.Score1)-(c.score2+t1.Score2)) as DIFF
from Table1 t1 inner join CTE c
on c.id+1=t1.id and ((t1.Team1 = c.team1 and t1.Team2 = c.Team2) or (t1.Team2 = c.team1 and t1.Team1 = c.Team2))
)
,CTE1 As
(
select * from CTE
union
select id,Team1,Team2,Score1,Score2,0,0,ABS(Score1-Score2) as DIFF from Table1 where id not in(select id from CTE)
)
select id,Team1,Team2,Score1,Score2,DIFF from CTE1

Answer 3

You could try this:
Edit: Fixed for team1 & team2 swaps.
; WITH CTE AS (
SELECT
Id
, Team1
, Team2
, Score1
, Score2
, ROW_NUMBER() OVER (PARTITION BY X.Teams ORDER BY ???) AS Row
FROM MyTable
CROSS APPLY (
SELECT
Team1 + '_' + Team2 -- Use something else than '_' if this caracter can exist in team's names
WHERE Team1 < Team2
UNION ALL
SELECT
Team2 + '_' + Team1
WHERE Team1 > Team2
) AS X(Teams)
)
SELECT
T1.Id
, T1.Team1
, T1.Team2
, T1.Score1
, T1.Score2
, ABS((T1.Score1 + ISNULL(T2.Score1, 0)) - (T1.Score2 + ISNULL(T2.Score2, 0))) AS Abs(DIFF)
FROM CTE AS T1
OUTER APPLY (
SELECT
SUM(T2.Score1) AS Score1
, SUM(T2.Score2) AS Score2
FROM CTE AS T2
WHERE T2.Teams = T1.Teams
AND T2.Row < T1.Row
) AS T2