postgresql - Dynamically add previous row value to current row value in SQL(Postgres)

Question

I have a table with the following structure:

id	col1	col2
1	1	0
2	1	1
3	1	0
4	1	2
5	1	1
6	1	2
7	1	1

Answer 1

You just need analytical function sum as follows:

select col1, col2, 
       Sum(col1 - col2) over (order by id) as col3
  from t1;