@Override
    public void addAlias(String name, Integer index) {
      names.add(name);
      indexes.add(index);
    }
SortCol.

An implementation of BucketSortCol which contains known aliases/indexes of equivalent columns
which data is determined to be sorted on.  Unlike aliases, and indexes the sort order is known
to be constant for all equivalent columns.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/physical/BucketingSortingCtx.java