带外键的NULL值

Question

I have 2 forms in php for adding the supplier and customer. On these forms I can add contact of supplier or customer. Now, I made foreign key on table contact since 1 supplier or 1 customer can have many contacts. But the problem is that I have 1 contact table, structured like this:

ID  |  telefon  |  name  |  mail  |  type_fk  | supplier_fk_id  |  customer_id_fk
------------------------------------------------------------------------------
1   |  123      | john   | mail   |     1     |       23        |      NULL
2   |  123234   | julie  | gfdh   |     3     |       NULL      |      45

So basically, I want that to be stored in one table, and right now I'm not sure if that was a good idea. Since when I add customer contacts I have NULL value in supplier_fk_id, and same this for the supplier but in customer_fk_id. I have foreign keys on update and on delete - cascade since I want those contacts to be deleted if the customer/supplier is deleted. If I remove the foreign keys in the database I won't have the database side check which I want. But I get error like this:

Error   
Error inserting:
Cannot add or update a child row: a foreign key constraint fails 
(`testbase`.`pro_contact`, CONSTRAINT `supplier_fk_id` FOREIGN KEY (`supplier_fk_id`) 
REFERENCES `pro_supplier` (`supplier_id`) ON DELETE CASCADE ON UPDATE CASCADE)

Any advice would be appreciated...

Answer 1

我认为根据您的决定，对SUPPLIER/CONTACTS使用ON DELETE SET NULL ，对CUSTOMER/CONTACTS ON DELETE CASCADE ，反之亦然