Question: This setup is for multiple addresses for one debtor. I have 2 fields for the debtor in my order table. debiteur\_id for the "default" value from the debtor table. If we choose another addres for the same debtor the debiteur\_id is null and aditional\_id is filled in with the value from aditional\_debiteur wich is linked to debtor. I hope someone gets it. 

My tables: 

```
Order
id debiteur_id amount aditional_id
1  null        2      1
2  1           3      null
3  2           1      null

debtor
id name         hnr place
1  myname       10  london
2  companyName  4   Enschede

Aditional_debiteur
id debiteur_id hnr place
1  1           22  amsterdam

```

What I want is to get all the orders linked (Direct or inderict) to an id from the debtor table. This because the order is from the same company only with another adress.
If I choose debor with id 1 I get this order results:

```
order_id name    amount 
1        myname  2
2        myname  3 

```

**Another result with debtor id 2:**

```
order_id name         amount 
3        companyName  1 

```

I have this query:

```
SELECT * FROM `Order` WHERE `debiteur_id` = '1' ORDER BY `id` ASC

```

This returns the result with the default debtor adress, I want to retrieve the other orders with the aditional\_id (wich are linked to the debtor with the debituer\_id) also.

Long story short. I want to retrieve all orders from the order table with an specific debtor from the debtor table.

Answer: 
```
SELECT
    o.id AS order_id
    ,d.name
    ,o.amount
    ,IFNULL(ad.hnr,d.hnr) AS hnr
FROM
    `Order` o
    LEFT JOIN Additional_debiteur ad
    ON o.aditional_id = ad.id
    AND ad.debiteur_id = 1
    INNER JOIN debtor d
    ON IFNULL(o.debiteur_id,ad.debiteur_id) = d.id
WHERE
    o.debiteur_id = 1
    OR ad.id IS NOT NULL
ORDER BY
    o.id ASC

```

Here is one way to do it.
Do you just want `OR`?

```
SELECT o.*
FROM `Order` o
WHERE 1 IN (debiteur_id, aditional_id)
ORDER BY id ASC

```

Note: If the ids are numeric, then you should not use single quotes for the values. I am assuming that the ids are, in fact, numeric.