mysql foreign key syntax / tutorial

Hi. Any body got an idea how to use hte foreign keys in mysql innodb tables and how whould the change affect the performance of the server? lets say i have Items table, Clients table, and Sales table the Sales table always stores ClientID and ItemID but not every client/item is there a sale can be deleted without harming the client nor the item. i guess (not sure at all) it should go like : ALTER TABLE Sales ADD FOREIGN KEY ClientID(ClientID) REFERENCES Clients(ClientID) ON DELETE RESTRICT; ALTER TABLE Sales ADD FOREIGN KEY ItemID(ItemID) REFERENCES Items(ItemID) ON DELETE RESTRICT; Am I correct? thanks.