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 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: