mysql查询sum的结果是null不是0，怎么回事？

先来看一下需求：

sql语句：

select  date_format(creatTime,"%Y-%m-%d") as days,count(id) as num,sum(money) as money 
from `order` group by days;

结果如下：解决方法：使用 CASE WHEN 字段 IS NOT NULL THEN 值 ELSE 0 END 示例代码：

select  date_format(creatTime,"%Y-%m-%d") as days,count(id) as num,
(CASE WHEN SUM(money) IS NOT NULL THEN SUM(money) ELSE 0 END) AS money 
from `order` group by days;

最终效果：