我可以在内部连接条件 sql 中使用子查询吗

Question

表（旅行）

| Id | Client_Id | Driver_Id | City_Id |     Status      |Request_at|


| 1  |     1     |    10     |    1    |     completed      |2013-10-01|

| 2  |     2     |    10     |    1    |     completed      |2013-10-02|

| 3  |     3     |    11     |    6    |     completed      |2013-10-03|

表（用户）

Users_Id    | Banned |  Role  |

|    1     |   No   | client |

|    2     |   Yes  | client |

|    3     |   No   | client |

|    4     |   No      | driver|

如果用户角色需要是客户端并且这些客户端应该被取消禁止，我如何才能加入这 2 个表（旅行、用户）。 我正在尝试使用子查询，但出现“单行子查询返回多行”错误并且不确定出了什么问题。

SELECT * FROM Trips
INNER JOIN users
ON client_id = (SELECT users_id from users 
                  where 
                  role = 'Client' and  banned = 'No');

Answer 1

不需要子选择，只需将这些条件放入连接条件即可。

SELECT * 
FROM Trips
  JOIN users ON trips.client_id = users.users_id 
            and users.role = 'Client' 
            and users.banned = 'No';

因为这是一个内连接，这相当于：

SELECT * 
FROM Trips
  JOIN users ON trips.client_id = users.users_id 
WHERE users.role = 'Client' 
  and users.banned = 'No';

如果您使用了外连接，这将不会有所不同

Answer 2

您不需要子查询
连接应该在 Trips 和 Users 之间，例如：

SELECT * 
FROM Trips
INNER JOIN users ON Trips.client_id = usres.users_id 
        and users.role = 'Client' 
        and  users.banned = 'No';

Answer 3

 SELECT *
 FROM Trips
 INNER JOIN Users ON [Trips].Id = [Users].User_Id AND [Users].Role = 'client' AND [Users].Banned = 'No'

Answer 4

试试

SELECT * FROM Trips
INNER JOIN users ON users.users_id = Trips.Client_ID
WHERE users.Banned = 'No' AND users.Role = 'client'