MySQL如何按天统计数据，没有记录的天自动补充0

思路：

1. 通过该语句可以实现指定日期到当前日期的日期列表数据，并用0填充要统计的sum字段

SELECT @cdate := date_add(@cdate,interval - 1 day) `date` , 0 as `sum`
from (SELECT @cdate :=date_add(CURDATE(),interval + 1 day) from <任意有数据表名>) t1 
where @cdate > '2017-08-03'

2. 要统计的SQL语句，如：

select DATE_FORMAT(createTime,'%Y-%m-%d') as `date`,sum(money) 
from payTable 
group by `date`

3. 合并两个结果集，并保证字段相同。完整代码如下：

select `date` ,max(`sum`) as `sum` from 
(
   SELECT @cdate := date_add(@cdate,interval - 1 day) `date` , 0 as `sum`
   from (SELECT @cdate :=date_add(CURDATE(),interval + 1 day) from <任意有数据表名>) t1 
   where @cdate > '2017-08-03'

   union all

   select DATE_FORMAT(createTime,'%Y-%m-%d') as `date`,sum(money) 
   from payTable 
   group by `date`

) _tmpAllTable 
group by `date`

以上SQL未考虑性能问题，在实际使用中慎重考虑