@Override
    public ScalarOperator visitSubfield(SubfieldOperator operator, Void context) {
        return shuttleIfUpdate(operator);
    }
@Test
    void testSubfieldOperator() {
        ColumnRefOperator column1 = new ColumnRefOperator(1, INT, "id", true);
        SubfieldOperator operator = new SubfieldOperator(column1, INT, Lists.newArrayList("a"));
        {
            ScalarOperator newOperator = shuttle.visitSubfield(operator, null);
            assertEquals(operator, newOperator);
        }
        {
            ScalarOperator newOperator = shuttle2.visitSubfield(operator, null);
            assertEquals(operator, newOperator);
        }
    }