Need suggestion for placing foreign keys in the databases I have the database for customers. The customers table is something like this

+------------------+
|     Customers    |
+------------------+
| id  (PK)         |
| business_email   |
| business_name    |
| customer_name    |
| payment_terms    |
| currency         |
| business_address |
| city             |
| state            |
| postal_code      |
| country          |
| phone            |
| created_at       |
| updated_at       |
+------------------+


Now I want to put the shipping address in my application where the customer can optionally mention his shipping address.S o I have made an extra table for shipping address like this

+------------------+
| Shipping Address |
+------------------+
| id  (PK)         |
| contact_name     |
| contact_address  |
| delivery_address |
| created_at       |
| updated_at       |
+------------------+


Now my problem is I am little bit confused in whose key should be foreign key in which table.I am strucked in this.So any help and suggestion will be highly appriciable.
Assuming a company can have more than one shipping address, the key would be a column added on Shipping Address table (aptly named 'customer_id' and the foreign key definition on the Shipping Address table. If you wanna avoid same address more than once, also add a unique key on shipping address table that can include (customer_id, contact_name) 

On an unrelated note, make sure your created_at and updated_at use timestamps ;)