@Override
  public final boolean equals(Object o) {
    if (this == o) {
      return true;
    }

    if (!(o instanceof Expression)) {
      return false;
    }

    return getOutputSymbol().equals(((Expression) o).getOutputSymbol());
  }
Sub-classes must not override this method.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/Expression.java