t-sql function like "filter" for sum(x) filter(condition) over (partition by - tsql

Question

I'm trying to sum a window with a filter. I saw something similar to
sum(x) filter(condition) over (partition by...)
but it does not seem to work in t-sql, SQL Server 2017.
Essentially, I want to sum the last 5 rows that have a condition on another column.
I've tried
sum(case when condition...) over (partition...)
and sum(cast(nullif(x))) over (partition...).
I've tried left joining the table with a where condition to filter out the condition.
All of the above will add the last 5 from the starting point of the current row with the condition.
What I want is from the current row. Add the last 5 values above that meet a condition.
Date| Value | Condition | Result
1-1 10 1
1-2 11 1
1-3 12 1
1-4 13 1
1-5 14 0
1-6 15 1
1-7 16 0
1-8 17 0 sum(15+13+12+11+10)
1-9 18 1 sum(18+15+13+12+11)
1-10 19 1 sum(19+18+15+13+12)
In the above example the condition I would want would be 1, ignoring the 0 but still having the "window" size be 5 non-0 values.

Answer 1

This can easily be achieved using a correlated sub query:
First, create and populate sample table (Please save us this step in your future questions):
DECLARE #T AS TABLE
(
[Date] Date,
[Value] int,
Condition bit
)
INSERT INTO #T ([Date], [Value], Condition) VALUES
('2019-01-01', 10, 1),
('2019-01-02', 11, 1),
('2019-01-03', 12, 1),
('2019-01-04', 13, 1),
('2019-01-05', 14, 0),
('2019-01-06', 15, 1),
('2019-01-07', 16, 0),
('2019-01-08', 17, 0),
('2019-01-09', 18, 1),
('2019-01-10', 19, 1)
The query:
SELECT [Date], [Value], Condition,
(
SELECT Sum([Value])
FROM
(
SELECT TOP 5 [Value]
FROM #T AS t1
WHERE Condition = 1
AND t1.[Date] <= t0.[Date]
-- If you want the sum to appear starting from a specific date, unremark the next row
--AND t0.[Date] > '2019-01-07'
ORDER BY [Date] DESC
) As t2
HAVING COUNT(*) = 5 -- there are at least 5 rows meeting the condition
) As Result
FROM #T As T0
Results:
Date Value Condition Result
2019-01-01 10 1
2019-01-02 11 1
2019-01-03 12 1
2019-01-04 13 1
2019-01-05 14 0
2019-01-06 15 1 61
2019-01-07 16 0 61
2019-01-08 17 0 61
2019-01-09 18 1 69
2019-01-10 19 1 77