How to find start date of loan delinquency sql?

Question

SQL

I have a table in this format:

Date 	     Customer   Deal   Currency Sum 
12.12.2019 	111110 	111111 	RUR 	12000 
25.12.2019 	111110 	111111 	RUR 	5000 
12.12.2019 	111110 	122222 	RUR 	10000 
12.01.2020 	111110 	111111 	RUR 	-10100 
20.11.2019 	220000 	222221 	RUR 	25000 
20.12.2019 	220000 	222221 	RUR 	-25000 
21.12.2019 	220000 	222221 	RUR 	20000 
29.12.2019 	111110 	122222 	RUR 	-10000

I output the amount of debt of people who are in arrears on the loan using this code:

select deal, sum(payment_sum) as "Невыпл_сум" from pdcl
having sum(payment_sum) > 0
group by deal

Now I need to display the start date of the delay (for example, for deal 111111 it is 12/12/2019) and just min(date) does not come out because it is looking for the minimum string, not the date

Answer 1

Running total (window functions).