Question

I want to make a link between a table customer and a table product by an IdProduct.

Example:

Create table customer(
idcustomer  INT not null,
name        Varchar(20),
idproduct   INT,
);

create table Product(
idproduct INT not null,
nameProduct varchar(40)
);

How can I link the two together like the foreign key system for, when I select a customer, I can get all his products? It’s a question about the structure of the database.

Answer 1

In mysql a foreign key is a special type of constraint. It is preferably created with the table, but can also be added afterwards. In this case, you might define the constraint as:

ALTER TABLE customer
ADD FOREIGN KEY (idproduct)
REFERENCES Product (idproduct);

(Note that you have to use the InnoDB engine to take advantage of FK’s in mysql. More here

However FK’s aren’t required to make a JOIN, which is how you would link the tables in a SELECT –

select c.idcustomer, c.name, p.nameproduct
from customer c
join Product p on p.idproduct=c.idproduct;