protected void addEquivalence(RexTableInputRef p1, RexTableInputRef p2, RexCall originalCond) {
      addEquivalence(p1, p2);
      equivalenceToOriginalNode.put(Pair.of(p1, p2), originalCond);
      equivalenceToOriginalNode.put(Pair.of(p2, p1), originalCond);
    }
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