mysql统计一年12个月的数据，当某个月没数据的时候自动补0

在mysql中如何去统计12个月的数据，并且给没有数据的月份设置为0 ？

因为每个人的业务都不太一样，所以如何统计数据这个就不说了，不过我相信能看到这篇文章的人应该都已经做好数据统计，只是统计的数据并不是完整的12个月的数据，有可能某些月份并没有数据，这时候需要给那些没有数据月份设置为0 ，那具体应该如何做呢？

首先介绍下大致思路：

我们要自己手动生成一列1~12月的数据，然后和你统计的数据进行左连接，利用mysql的 ifnull 函数将空值转化成0，这样就能达到我们想要的目的了

具体看下应该怎么做吧

第一步：生成1~12月的一列数据

这里的 #{year}是mybaties里面的参数，因为要通过年份去筛选数据，所以做成了变量形式的

SELECT CONCAT(#{year},'-01') AS date UNION
SELECT CONCAT(#{year},'-02') AS date UNION
SELECT CONCAT(#{year},'-03') AS date UNION
SELECT CONCAT(#{year},'-04') AS date UNION
SELECT CONCAT(#{year},'-05') AS date UNION
SELECT CONCAT(#{year},'-06') AS date UNION
SELECT CONCAT(#{year},'-07') AS date UNION
SELECT CONCAT(#{year},'-08') AS date UNION
SELECT CONCAT(#{year},'-09') AS date UNION
SELECT CONCAT(#{year},'-10') AS date UNION
SELECT CONCAT(#{year},'-11') AS date UNION
SELECT CONCAT(#{year},'-12') AS date

第二步：和统计的数据进行左连接

select * from 
(
SELECT CONCAT(#{year},'-01') AS date UNION
SELECT CONCAT(#{year},'-02') AS date UNION
SELECT CONCAT(#{year},'-03') AS date UNION
SELECT CONCAT(#{year},'-04') AS date UNION
SELECT CONCAT(#{year},'-05') AS date UNION
SELECT CONCAT(#{year},'-06') AS date UNION
SELECT CONCAT(#{year},'-07') AS date UNION
SELECT CONCAT(#{year},'-08') AS date UNION
SELECT CONCAT(#{year},'-09') AS date UNION
SELECT CONCAT(#{year},'-10') AS date UNION
SELECT CONCAT(#{year},'-11') AS date UNION
SELECT CONCAT(#{year},'-12') AS date

)a

left join

(select  count(*) num,date from ......) b   //这里是你的数据统计sql，每个人不一样

on a.date = b.date    

第三步：将空值转化为0

select 
ifnull(b.num,0),a.date
 from 
(
SELECT CONCAT(#{year},'-01') AS date UNION
SELECT CONCAT(#{year},'-02') AS date UNION
SELECT CONCAT(#{year},'-03') AS date UNION
SELECT CONCAT(#{year},'-04') AS date UNION
SELECT CONCAT(#{year},'-05') AS date UNION
SELECT CONCAT(#{year},'-06') AS date UNION
SELECT CONCAT(#{year},'-07') AS date UNION
SELECT CONCAT(#{year},'-08') AS date UNION
SELECT CONCAT(#{year},'-09') AS date UNION
SELECT CONCAT(#{year},'-10') AS date UNION
SELECT CONCAT(#{year},'-11') AS date UNION
SELECT CONCAT(#{year},'-12') AS date

)a

left join

(select  count(*) num,date from ......) b   //这里是你的数据统计sql，每个人不一样

on a.date = b.date    

最后给大家看下我做的使用效果

好了，就这样，有什么问题，可以加群：798733709 问