@Override
  public SortExchange copy(RelTraitSet traitSet, RelNode newInput, RelDistribution newDistribution,
          RelCollation newCollation) {
    return new HiveSortExchange(getCluster(), traitSet, newInput,
            newDistribution, newCollation, keys);
  }
Creates a HiveSortExchange.

@param input     Input relational expression
@param distribution Distribution specification
@param collation Collation specification
@param keys Keys specification
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/reloperators/HiveSortExchange.java