public void onMatch(RelOptRuleCall call) {
          JoinRel join = (JoinRel) call.rels[0];
          List<RexNode> expList = new ArrayList<RexNode>(Arrays.asList(join.getChildExps()));
          if (reduceExpressions(join, expList)) {
            call.transformTo(
                new JoinRel(
                    join.getCluster(),
                    join.getLeft(),
                    join.getRight(),
                    expList.get(0),
                    join.getJoinType(),
                    join.getVariablesStopped()));

            // New plan is absolutely better than old plan.
            call.getPlanner().setImportance(join, 0.0);
          }
        }