HiveQL and rank()

Question

I can\'t understand HiveQL rank(). I\'ve found a couple of implementations of rank UDF\'s on the WWW, such as Edward\'s nice example. I can load and access the functions, bu

Answer 1

If you have a evaluate function as below, assuming you are using the function directly form the guide you mentioned,

private long counter;
@Override
  public Object evaluate(DeferredObject[] currentKey) throws HiveException {
    if (!sameAsPreviousKey(currentKey)) {
      this.counter = 0;
      copyToPreviousKey(currentKey);
    }

    return new Long(++this.counter);
  }

try changing it to the following, so that the counter is not reset when it finds a new volume, rather you don't increment if you find the same volume but increment only when it finds a new volume.

private long counter;
@Override
  public Object evaluate(DeferredObject[] currentKey) throws HiveException {
    //when not same as previous key you rather increment
    if (!sameAsPreviousKey(currentKey)) {
      this.counter ++;
      copyToPreviousKey(currentKey);
    }
    //else you keep the counter as it is
    return new Long(++this.counter);
 }

Tell me if this helps.

Answer 2

With the Windowing and Analytics functions introduced in Hive 0.11, you can use:

select SalesRepId, volume as amount , rank() over (order by V.volume desc) as rank from 
(select SalesRepId,sum(amount) as volume from purchases group by SalesRepId) V;