How to reset running total for a column if null is present?

Question

I have a table as below

Customer	Start_Date_of_Month	Sales_order_count	Value
A	01/06/2022	3	null
B	01/07/2022	2	null
A	01/07/2022	0	1
A	01/08/2022	0	1
B	01/08/2022	0	1
A	01/09/2022	3	null
B	01/09/2022	1	null
A	01/10/2022	1	null
B	01/10/2022	0	1
A	01/11/2022	0	1

I'm trying to calculate the running total of Value column with respect to Customer and by Start_Date _of_Month in ascending order. If null is present in the Value column, the running total has to be reset

The output would be like

Customer	Start_Date_of_Month	Sales_order_count	Running_Total
A	01/06/2022	3	null
A	01/07/2022	0	1
A	01/08/2022	0	2
A	01/09/2022	3	null
A	01/10/2022	1	null
A	01/11/2022	0	1
B	01/07/2022	2	null
B	01/08/2022	0	1
B	01/09/2022	1	null
B	01/10/2022	0	1

Thanks in Advance

Answer 1

You could define groups for each customer whenever a null value is found, then use the running sum partitioned by these groups, try the following for MySQL 8+:

select Customer, Start_Date_of_Month, Sales_order_count,
  sum(Value) over (partition by Customer, grp order by Start_Date_of_Month) Running_Total
from
(
  select *,
    sum(value is null) over (partition by Customer order by Start_Date_of_Month) grp
  from table_name
) T
order by Customer, Start_Date_of_Month  

See demo