Question

I have the following SQL statement:

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'

This query delivers the columns from the table “Cars” twice, but with different values for the ID from the Car table (the purpose of the query is to map the values to see what the Car.ID would be id the material would change from leather to plastic).

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

However, I would like to output only the ID columns (not the material columns), like this:

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

I have not been able to do this, as I haven’t found a way to refer to the ID column of the inner query in any way. For example

SELECT id, innertable.id
(...)

or

SELECT id, auto.id
(...)

or

SELECT id, id_1
(...)

don’t seem to work. How can achieve this?

Answer 1

Try explicitly listing the column names of the inner table in the select statement. Like:

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

and then in the main select:

SELECT innertable.autoid ....