Suppose you want to compute A,Bsum(C) on a relation s which is stored partitioned on s.B. Explain

Suppose you want to compute A,Bγsum(C) on a relation s which is stored partitioned on s.B. Explain how you would do it efficiently, minimizing/avoiding repartitioning, if the number of distinct s.B values is large, and the distribution of number of tuples with each s.B value is relatively uniform.