Oracle ECC : How to apply group by clause in a dataset ?

1. I have a Dataset, With Assignment details and the Elements Details, Each element has a pay value. Which means the first result table displays, Lets say an Assignment1 is having five element name . So there will be five records for the assignment number.

Question :

I want to have a result table based on group by clause on Assignment number and display the Sum(pay value) using the same dataset. Here there will be one record per assignment number. How to achieve this in ECC ? Please provide the steps to achieve this. Thank you.