按月分组，包括空月

Question

我想选择每月的所有订单金额。我知道这对于按月分组效果很好，但仅适用于有订单的月份。现在我还想要没有订单的月份，这样我就可以获得所有月份。

这是我的查询：

SELECT SUM(VerkoopfactBedrag) AS bedrag, DATE_FORMAT(VerkoopfactDatum,'%M') AS date 
FROM verkoopfacturen 
WHERE Verkoopfact_UserId = 12 
   AND VerkoopfactDatum BETWEEN '2011-01-01' AND '2011-12-30' 
GROUP BY MONTH(VerkoopfactDatum)

因此，当一个月的结果为 0 时，我想查看值为 0 的月份，但现在该月份没有显示。

这可能吗？

Answer 1

实现此目的的一种方法是创建并填充一个包含连续月份的表。

然后您可以使用该表OUTER JOIN。

例如：

drop table if exists all_months;

create table all_months (a_month_id int unsigned PRIMARY KEY,a_month varchar(20) NOT NULL, UNIQUE KEY `all_months_uidx1` (a_month));

insert into all_months values (1,'January');
insert into all_months values (2,'February');
insert into all_months values (3,'March');
insert into all_months values (4,'April');
insert into all_months values (5,'May');
insert into all_months values (6,'June');
insert into all_months values (7,'July');
insert into all_months values (8,'August');
insert into all_months values (9,'September');
insert into all_months values (10,'October');
insert into all_months values (11,'November');
insert into all_months values (12,'December');

SELECT SUM(IFNULL(t1.VerkoopfactBedrag,0)) AS bedrag, 
am.a_month AS date
from
(
select
ifnull(vn.VerkoopfactBedrag,0) as VerkoopfactBedrag,
cast(DATE_FORMAT(VerkoopfactDatum, '%M') as char) as mdate
FROM verkoopfacturen vn
WHERE Verkoopfact_UserId = 12 
AND VerkoopfactDatum BETWEEN '2011-01-01' AND '2011-12-31' 
GROUP BY DATE_FORMAT(VerkoopfactDatum, '%M')
) t1 RIGHT OUTER JOIN all_months am on t1.mdate = am.a_month
group by am.a_month
order by a_month_id asc;

PS 不确定您是否对 Oudejaarsavond 有任何反对，但 12 月有 31 天；-)

Answer 2

在寻找一个简单的解决方案后，我终于找到了这个我认为很简单的解决方案。这将并列显示去年和今年的销售额。

select 
       date_format(current_date - INTERVAL 1 YEAR,'%Y') as LAST_YR,
       date_format(NOW(),'%Y') as THIS_YR,
       monthname(date) as month,
       sum(case when year(date) = date_format(current_date - INTERVAL 1 YEAR,'%Y') then amount else 0 end) as sales_ly,
       sum(case when year(date) = DATE_FORMAT(NOW(),'%Y') then amount else 0 end) as sales_ty
from tablename
where date between date_format(current_date - INTERVAL 1 YEAR,'%Y-%01-%01')
and date_format(current_date, '%Y-%12-%31')
group by monthname(date)
order by max(month(date));