Question

我有这个查询，我想在计数为0时返回一行

SELECT count(day) as count, day
FROM `table`
GROUP BY `day`

其他stackoverflow答案说我需要进行左连接但是我不知道如何在这种情况下这样做。

Answer 1

create table theDays
(   aDay varchar(20) not null
);

create table sales
(   id int auto_increment primary key,
    aDay varchar(20) not null,
    prodId int not null,
    qty int not null
);

insert theDays values ('sunday'),('monday'),('tuesday'),('wednesday'),('thursday'),('friday'),('saturday');
insert sales(aDay,prodId,qty) values ('tuesday',101,4),('thursday',107,2);

select d.aDay
from theDays d
left outer join sales s
on d.aDay=s.aDay
where s.aDay is null

+-----------+
| aDay      |
+-----------+
| sunday    |
| monday    |
| wednesday |
| friday    |
| saturday  |
+-----------+

mysql group by show count 0不确定我是否可以离开这里加入

1 个答案: