Welcome to a new feature, SQL Puzzlers! Hope you enjoy them. Follow the link above to see all that we have.
Here is a puzzler for the SQL types in the crowd
Given this dataset:

How would you code a running total?

I've gotten you started, here is the code that produces the first window, all you have to do is code the RunningTotal column.
declare @t table (RowID int identity, Docdate date, Sales numeric(19,2))
insert into @t (docdate, Sales) values ('1/1/2019',100)
insert into @t (docdate, Sales) values ('1/2/2019',200)
insert into @t (docdate, Sales) values ('1/3/2019',300)
insert into @t (docdate, Sales) values ('1/4/2019',400)
insert into @t (docdate, Sales) values ('1/5/2019',500)
select *
from @t
order by docdate
The answer is below, peek at your own peril.