mysql statement explained

[mindapolis]

I just want to make sure I'm understanding the following code correctly.  The primary key, order_number, from the orders table is now the foreign key in the customers table, correct? 

 

 

ALTER TABLE `customers` ADD FOREIGN KEY ( `customers_id` ) REFERENCES `auntievics`.`orders` (
`order_number`
);

[fenway]

Yes, but I don't see how that's an "explanation".