val orders = sc.textFile("/public/retail_db/orders")
val ordersMap = orders.
  map(o => (o.split(",")(0).toInt, o))

val orderItems = sc.textFile("/public/retail_db/order_items")
val orderItemsMap = orderItems.
  map(oi => (oi.split(",")(1).toInt, oi))

val ordersJoin = ordersMap.
  join(orderItemsMap)
val ordersLeftOuterJoin = ordersMap.
  leftOuterJoin(orderItemsMap)

ordersJoin.count
ordersLeftOuterJoin.count

ordersLeftOuterJoin.
  take(100).
  foreach(println)