SQL cumulative sum until a flag value and resetting the sum - sql

Question

I'm still learning SQL and I'm trying to figure out a problem that I wasn't able to solve. So my problem is that I'm trying to select a table(let say Expense), ordered by date and in the table I have a column named Charged and I want to add charges to be cumulative(This part I figured out). However after that I have another column that will be acting as a flag called PayOut. When the PayOut value is 1 I want the summation of Charged(SumValue) to reset to zero. How would I do this? Here is what I have tried and the current output I get and what output I want. Note: I saw some posts using CTE's but wasn't the same scenario and more complex.
select ex.date,
ex.Charged,
(case when(ex.PayOut=1) then 0
else sum(ex.Charged) over (order by ex.date)end) as SumValue,
ex.PayOut
from Expense ex
order by ex.date asc
The data looks like this
Date Charged PayOut
01/10/2018 10 0
01/20/2018 5 0
01/30/2018 3 0
02/01/2018 0 1
02/11/2018 12 0
02/21/2018 15 0
Output I get
Date Charged PayOut SumValue
01/10/2018 10 0 10
01/20/2018 5 0 15
01/30/2018 3 0 18
02/01/2018 0 1 0
02/11/2018 12 0 30
02/21/2018 15 0 45
Output Wanted
Date Charged PayOut SumValue
01/10/2018 10 0 10
01/20/2018 5 0 15
01/30/2018 3 0 18
02/01/2018 0 1 0
02/11/2018 12 0 12
02/21/2018 15 0 27

Answer 1

Just create group from your PayOut Column and use it as a partition in OVER
WITH Expense AS (
SELECT CAST('01/10/2018' AS DATE) AS Date, 10 AS Charged, 0 AS PayOut
UNION ALL SELECT CAST('01/20/2018' AS DATE), 5, 0
UNION ALL SELECT CAST('01/30/2018' AS DATE), 3, 0
UNION ALL SELECT CAST('02/01/2018' AS DATE), 0, 1
UNION ALL SELECT CAST('02/11/2018' AS DATE), 12, 0
UNION ALL SELECT CAST('02/21/2018' AS DATE), 15, 0
)
SELECT
dat.date
,dat.Charged
,dat.PayOut
,dat.PayOutGroup
,SUM(dat.Charged) OVER (PARTITION BY dat.PayOutGroup ORDER BY dat.date) as SumValue
FROM (
SELECT
e.date
,e.Charged
,e.PayOut
,SUM(e.PayOut) OVER (ORDER BY e.date) AS PayOutGroup
FROM Expense e
) dat