public static OptExpression bind(Pattern pattern, GroupExpression groupExpression) {
        Binder binder = new Binder(pattern, groupExpression);
        return binder.next();
    }
@Test
    public void testBinder2() {
        OptExpression expr = OptExpression.create(new MockOperator(OperatorType.LOGICAL_JOIN),
                new OptExpression(new MockOperator(OperatorType.LOGICAL_OLAP_SCAN)),
                new OptExpression(new MockOperator(OperatorType.LOGICAL_OLAP_SCAN)));

        Pattern pattern = Pattern.create(OperatorType.PATTERN_LEAF)
                .addChildren(Pattern.create(OperatorType.LOGICAL_JOIN))
                .addChildren(Pattern.create(OperatorType.PATTERN_LEAF));

        Memo memo = new Memo();
        OptExpression result = Binder.bind(pattern, memo.init(expr));

        assertNull(result);
    }