@Override
  public int compare(VectorHashKeyWrapperBase o1, VectorHashKeyWrapperBase o2) {
    for (Comparator<VectorHashKeyWrapperBase> comparator : comparators) {
      int c = comparator.compare(o1, o2);
      if (c != 0) {
        return c;
      }
    }
    return 0;
  }
Compare {@link VectorHashKeyWrapperBase} instances only by one column.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/wrapper/VectorHashKeyWrapperGeneralComparator.java