You can do this when creating the table:

CREATE TABLE Orders ( OrderID int NOT NULL, OrderNumber int NOT NULL, PersonID int, PRIMARY KEY (OrderID), FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) );

Or by changing the form:

ALTER TABLE Orders ADD FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

Also seethis tutorial.

First, you need to add a new column to the tableorderbook

ALTER TABLE orderbook ADD payment_request_id INT(10) unsigned AFTER ID;

Then add a constraint that defines the foreign key

ALTER TABLE orderbook ADD CONSTRAINT fk_orderbook FOREIGN KEY (payment_request_id) REFERENCES payment_request (id);

refer to:

• MySQL change table