Foreign Key를 세팅하기 전에는 아래 데이타가 들어감

insert into customer.Orders (OrderDate, CustomerID, ProductID) values (now(), 4, 2);

alter table cusomer.orders
add foreign key (CustomerID) references Customer(ID);

alter table customer.orders
add foreign key (ProductID) references Products(ID);

위와 같이 Foreign Key를 세팅해 두면 같은 insert문장이라도  에러가 남.

insert into customer.Orders (OrderDate, CustomerID, ProductID) values (now(), 4, 2);

https://youtu.be/9Pzj7Aj25lw?list=PLD20298E653A970F8&t=2693