Yes, you would type that in the calculated field. You can use almost any SQL function in a calculated field and it will take it. Search the site for windowing functions and you will find some examples. If you get stuck, you can show me what you have and I can help.
Here’s a site that explains how they work.
and here’s a good example of a windowing function in action. It’s using ROW_NUMBER() instead of SUM() but it’s the same basic concept.