The reason you are having trouble writing this statement is that it is not the type of statement that SQL is really supposed to handle. And the reason that it is not the type of statement that SQL is really supposed to handle is most likely due to your table structure not being designed properly.
To do this with your current schema, you'll have to write a SELECT statement that join two instances of this table to itself, on sequential ID values. I could give you code for this, but even then I suspect it is not going to achieve the result that you want.
How about you give us a few more details regarding the business problem you are trying to solve?
If it's not practically useful, then it's practically useless.
Yes, I know the tables are not structure well. It's what I got and I didn't create it.
What I'm trying to achieve is:
The table represents payments that have been entered into our system. The top row represents a "Pledge" (like an IOU), and the bottom row represents the "Payment" to that "Pledge". The way the db is structures, it adds 2 entries (don't know why their did that way). So, if a person "Pledges" an amount, then pays off the entire amount, I just want to show the "Payment". If the person "Pledges" and pays off partial amount, I want to reduce the "Pledge" and show the payment as well. I have the logic for the reduction, just don't know how to display just the payment if the entire pledge was paid.