public CassandraSort(RelOptCluster cluster, RelTraitSet traitSet,

      RelNode child, RelCollation collation) {

    super(cluster, traitSet, child, collation, null, null);



    assert getConvention() == CassandraRel.CONVENTION;

    assert getConvention() == child.getConvention();

  }



  @Override public RelOptCost computeSelfCost(RelOptPlanner planner,

      RelMetadataQuery mq) {

    RelOptCost cost = super.computeSelfCost(planner, mq);

    if (!collation.getFieldCollations().isEmpty()) {

      return cost.multiplyBy(0.05);

    } else {

      return cost;

    }

  }