remote exchange (GATHER, SINGLE, [])
    local exchange (GATHER, UNKNOWN, [])
        remote exchange (REPARTITION, ROUND_ROBIN, [])
            final SortAggregate over (ss_customer_sk, ss_item_sk)
                local exchange (GATHER, SINGLE, [])
                    partial SortAggregate over (ss_customer_sk, ss_item_sk)
                        join (LEFT, REPLICATED):
                            join (INNER, REPLICATED):
                                scan store_sales_item_customer
                                local exchange (GATHER, SINGLE, [])
                                    remote exchange (REPLICATE, BROADCAST, [])
                                        scan store_returns
                            local exchange (GATHER, SINGLE, [])
                                remote exchange (REPLICATE, BROADCAST, [])
                                    scan item
