Question

我有以下SQL语句：


SELECT *
FROM   cars car
       LEFT JOIN (SELECT *
                  FROM   cars auto
                         LEFT JOIN steeringwheels sw
                           ON auto.steeringwheelid = sw.ID
                  WHERE  material = 'leather') innertable
         ON innertable.ID = car.ID
       LEFT JOIN steeringwheels sw
         ON auto.steeringwheelid = sw.ID
WHERE sw.material='plastic'

此查询提供表“Cars”中的列两次，但是来自Car表的ID具有不同的值（查询的目的是映射值以查看Car.ID将ID为材料的内容将从皮革变为塑料）。


------------------------------------
| ID | material | ID_1 | material_1 |
-------------------------------------
| 1  | leather  | 4    | plastic    |
| 2  | leather  | 7    | plastic    |
-------------------------------------

但是，我想只输出ID列（而不是材料列），如下所示：


-------------
| ID | ID_1 | 
-------------
| 1  |  4   |
| 2  |  7   | 
-------------

我无法做到这一点，因为我没有找到以任何方式引用内部查询的ID列的方法。例如


SELECT id, innertable.id
(...)

或


SELECT id, auto.id
(...)

或


SELECT id, id_1
(...)

似乎没有用。怎么能实现这个目标？

Answer 1

尝试在select语句中显式列出内部表的列名。像：

...(SELECT auto.ID autoid, auto.Whatever)....

然后在主要选择：

SELECT innertable.autoid ....

Answer 2

这就是你要追求的吗？

SELECT auto_id, steeringwheel_id
  FROM cars car 
       LEFT JOIN (SELECT auto.ID AS auto_id, sw1.id AS steeringwheel_id
                  FROM   cars auto 
                         LEFT JOIN steeringwheels sw1
                           ON auto.steeringwheelid = sw1.ID 
                  WHERE  material = 'leather') innertable 
         ON innertable.auto_ID = car.ID 
       LEFT JOIN steeringwheels sw2
         ON auto.steeringwheelid = sw2.ID 
  WHERE sw.material='plastic'

Oracle PL / SQL：引用内部联接查询中的列名

2 个答案: