SQL SERVER COUNT LEAD Condition Group BY - sql

Question

I am trying to find a way to count based on groups and I was not able to figure out a way without having to use a Cursor. Since using a Cursor will be relatively slow I was hoping there might be a better way.
Simplified the data is structured as follows:
+----+--------+-------+--------+
| ID | NEXTID | RowNo | Status |
+----+--------+-------+--------+
| 1 | 2 | 1 | 1 |
| 2 | 3 | 1 | 1 |
| 3 | 4 | 1 | 0 |
| 4 | | 1 | 1 |
| 1 | 2 | 2 | 0 |
| 2 | 3 | 2 | 1 |
| 3 | 4 | 2 | 1 |
| 4 | | 2 | 1 |
| 1 | 2 | 3 | 1 |
| 2 | 3 | 3 | 1 |
| 3 | 4 | 3 | 1 |
| 4 | | 3 | 1 |
+----+--------+-------+--------+
I now want to COUNT the Status column in groups resulting in:
+-----+-------------+
| Row | StatusCount |
+-----+-------------+
| 1 | 2 |
| 1 | 1 |
| 2 | 3 |
| 3 | 4 |
+-----+-------------+
For Testing purposes I creating the following code:
SELECT
ID,
NEXTID,
RowNo,
Status,
LEAD(ID,1,0)
OVER (ORDER BY RowNo,ID) AS LEADER
INTO #TestTable
FROM
(
VALUES
(1, 2, 1, 1),
(2, 3, 1, 1),
(3, 4, 1, 0),
(4, '', 1, 1),
(1, 2, 2, 0),
(2, 3, 2, 1),
(3, 4, 2, 1),
(4, '', 2, 1),
(1, 2, 3, 1),
(2, 3, 3, 1),
(3, 4, 3, 1),
(4, '', 3, 1)
)
AS TestTable(
ID,
NEXTID,
RowNo,
Status);
GO
SELECT
RowNo,
Count(Status) AS StatusCount
FROM #TestTable
WHERE
Status = 1
GROUP BY
RowNo
This results in
+-----+-------------+
| Row | StatusCount |
+-----+-------------+
| 1 | 3 |
| 2 | 3 |
| 3 | 4 |
+-----+-------------+
Not separating the first row. I do realise that I need another GROUP BY condition but I can not figure out the appropriate condition.
Thank you very much for your help. If this has already been answered I was unable to find the topic and hints will also be appreciated.
With kind regards
freubau

Answer 1

You can identify the groups by doing a cumulative sum of the zeros up to each number. Then, the rest is just aggregation:
select rowno, count(*)
from (select t.*,
sum(case when status = 0 then 1 else 0 end) over (partition by rowno order by id) as grp
from #TestTable t
) t
where status = 1
group by rowno, grp
order by rowno, grp;
Here is a rex tester for it.