THINPHP5.1 sql 查询不等于空的写法

以下写法起作用
SELECT * FROM `order_2020_10` WHERE (  `state` >= 810  AND `state` <= 850  AND ( complaint_result  != NULL ) ) AND `order_2020_10`.`delete_time` IS NULL

以下写法不起作用

SELECT * FROM `order_2020_10` WHERE (  `state` >= 810  AND `state` <= 850  AND ( complaint_result is not null ) ) AND `order_2020_10`.`delete_time` IS NULL