When altering the 'orders' table, you need to add a foreign key constraint named $\text{'}$fk$\_$order$\_$customer' on the 'customer$\_$id$\text{'}$ column, with cascading deletes to the 'customers' table. Fill in the blank to complete the code snippet.

ALTER TABLE orders

ADD fk$\_$order$\_$customer

KEY $($customer$\_$id$)$ REFERENCES customers$($id$)$