Question

SELECT D.Name,D.Id
FROM category_devices AS CD JOIN
     Devices AS D
     ON CD.deviceId = D.Id
Where CD.DeviceId = D.Id AND D.AppId =2

这是我的查询，我想显示CD.DeviceId！= D.Id的所有设备。上面的查询显示了所有相等的设备，如何将该查询转换为不等于？

SELECT D.Name,D.Id
FROM category_devices AS CD JOIN
     Devices AS D
     ON CD.deviceId = D.Id
Where CD.DeviceId = D.Id AND D.AppId =2

Answer 1

您可以使用LEFT JOIN和WHERE：

SELECT D.Name, D.Id
FROM category_devices CD LEFT JOIN
     Devices D
     ON CD.deviceId = D.Id AND D.AppId = 2
WHERE D.Id IS NULL;

但是，由于没有匹配项，因此只会在NULL中返回SELECT值。想必您想要这样的东西：

SELECT CD.*
FROM category_devices CD LEFT JOIN
     Devices D
     ON CD.deviceId = D.Id AND D.AppId = 2
WHERE D.Id IS NULL;

Answer 2

尚不清楚您想要什么，但是如果您想知道category_devices中的信息，而不是设备中的信息，以及设备中但category_devices信息中的信息，则不知道-

drop table if exists category_devices,devices;

create table category_devices(deviceId int);
create table devices(id int,name varchar(2));
insert into category_devices values (1),(4);
insert into devices values (1,'aa'),(2,'bb'),(3,'cc');

select cd.deviceid,d.id,d.name
from category_devices cd
left join devices d on cd.deviceid = d.id
where d.id is null
union
select cd.deviceid,d.id,d.name
from devices d
left join category_devices cd on cd.deviceid = d.id
where cd.deviceid is null;

+----------+------+------+
| deviceid | id   | name |
+----------+------+------+
|        4 | NULL | NULL |
|     NULL |    2 | bb   |
|     NULL |    3 | cc   |
+----------+------+------+
3 rows in set (0.00 sec)

Answer 3

使用NOT LIKE运算符

SELECT D.Name,D.Id
FROM category_devices AS CD JOIN
 Devices AS D
 ON CD.deviceId = D.Id
Where CD.DeviceId NOT LIKE D.Id AND D.AppId =2

更多信息，请点击SQL docs

如何将此查询转换为不等于版本

3 个答案: