Grouping in SQL Server - sql-server

Question

I have data similar to below. I need to group the status column based on the occurrence of data.
Id Status Value
1 K 1
2 K 3
3 K 2
4 B 2
5 B 3
6 K 6
7 J 5
8 J 2
I want data as below
Status Value
K 6
B 5
K 6
J 7
I need the cumulative sum of the value column.In the status column if the data is same consecutively, then I need to add the value columns. I cannot apply group by. In the example given K is repeated twice, because they are not consecutive.
I have tried below query, but it doesn't work as required.
select Status,
(select sum(value)
from table t2
where
t2.Status = t.Status and
t2.SNO <= t.SNO
) as total
from table t;

Answer 1

This is a Gaps and Islands Question
I tackle these by using the incrementing Id and combing this with ROW_NUMBER window function
--Using a CTE just to replicate the sample data
;WITH cteX (Id,Status,Value)
AS(
SELECT 1,'K', 1 UNION ALL
SELECT 2,'K', 3 UNION ALL
SELECT 3,'K', 2 UNION ALL
SELECT 4,'B', 2 UNION ALL
SELECT 5,'B', 3 UNION ALL
SELECT 6,'K', 6 UNION ALL
SELECT 7,'J', 5 UNION ALL
SELECT 8,'J', 2
)
SELECT
Grp = Id - ROW_NUMBER()OVER( PARTITION BY X.Status ORDER BY X.Id)
, X.Id
, X.Status
, X.Value
FROM
cteX X
ORDER BY
X.Id
This gives this result set, note the Grp column
Grp Id Status Value
------- ------- ------- -------
0 1 K 1
0 2 K 3
0 3 K 2
3 4 B 2
3 5 B 3
2 6 K 6
6 7 J 5
6 8 J 2
Then combine with a CTE or derived table you can get your expected output
--Using a CTE just to replicate the sample data
;WITH cteX (Id,Status,Value)
AS(
SELECT 1,'K', 1 UNION ALL
SELECT 2,'K', 3 UNION ALL
SELECT 3,'K', 2 UNION ALL
SELECT 4,'B', 2 UNION ALL
SELECT 5,'B', 3 UNION ALL
SELECT 6,'K', 6 UNION ALL
SELECT 7,'J', 5 UNION ALL
SELECT 8,'J', 2
)
SELECT Y.Status
, Value = SUM(Y.Value)
FROM
(
SELECT TOP 100 PERCENT
Grp = Id - ROW_NUMBER()OVER( PARTITION BY X.Status ORDER BY X.Id)
, X.Id
, X.Status
, X.Value
FROM
cteX X
ORDER BY
X.Id
) Y
GROUP BY
Y.Grp, Y.Status
Output
Status Value
------- -------
B 5
J 7
K 6
K 6
Update Question include "Preserve order" solution
Just include an Order by MIN(Id)
--Using a CTE just to replicate the sample data
;WITH cteX (Id,Status,Value)
AS(
SELECT 1,'K', 1 UNION ALL
SELECT 2,'K', 3 UNION ALL
SELECT 3,'K', 2 UNION ALL
SELECT 4,'B', 2 UNION ALL
SELECT 5,'B', 3 UNION ALL
SELECT 6,'K', 6 UNION ALL
SELECT 7,'J', 5 UNION ALL
SELECT 8,'J', 2
)
SELECT
Y.[Status]
,[Value] = SUM(Y.[Value])
FROM
(
SELECT
Grp = Id - ROW_NUMBER()OVER( PARTITION BY X.[Status] ORDER BY X.Id)
, X.Id
, X.[Status]
, X.[Value]
FROM
cteX X
) Y
GROUP BY
Y.Grp, Y.[Status]
ORDER BY
MIN(Y.Id) --preserve the Status Order
Output
Status Value
------- -------
K 6
B 5
K 6
J 7