[mysql基础及优化](https://www.kancloud.cn/book/a173512/mysql/edit) 插入查询更新等操作条件是null时不能用=（=表示null字符串），需要用is null条件 ``` select id from `shop_goods` where `brand_id` is NULL; update `shop_goods` set `brand_id`='1' where `brand_id` is NULL; ```