@Override
    public RelOptRule toRule() {
      return new CommonRelSubExprRegisterRule(this.operandSupplier());
    }
A predicate determining if a relational expression is interesting.

The notion of interesting is loosely defined on purpose since it may change as the API evolves. At the moment an
expression is considered interesting if it contains at least one of the following RelNode types:
<ul>
  <li>{@link Join}</li>
  <li>{@link Aggregate}</li>
  <li>{@link Filter}</li>
</ul>
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/CommonRelSubExprRegisterRule.java