protected Map<RexTableInputRef, Set<RexTableInputRef>> getEquivalenceClassesMap() {
      return nodeToEquivalenceClass;
    }
Class representing an equivalence class, i.e., a set of equivalent columns

TODO: This is a subset of a private class in materialized view rewriting
in Calcite. It should be moved to its own class in Calcite so it can be
accessible here.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/HiveRelOptUtil.java