On Mon, 10 May 2004 11:15:25 -0300 "Ronan Lucio" <[EMAIL PROTECTED]> wrote:
> Is the Primary Key Column mandatory? > > Supposing: > If I have two tables: Clients and Cars, and a third table > Clients_R_Cars, that is a relationship between Clients and Cars. > > I only need to know what cars the clients have. > So, I just need to two columns "CliCar_ClientsID" and > "CliCar_CarsID", the will be my index keys. > > Even thus do I need to create a Primary Key Column "CliCar_ID"? It is not "mandatory" to have a primary key, but you will have to handle duplicate rows in your front end program. Having primary keys is generally a good idea. In the situation that you are talking about, you can have a composite primary key (a primary key with more than one colunm) in your Clients_R_Cars table that is (Client_ID, Car_ID). This says that in your Clients_R_Cars table no two rows can have the same Client_Id AND Car_ID. Not sure if this is what you want or not. CREATE TABLE Clients_R_Cars ( Client_ID INT NOT NULL, Car_ID INT NOT NULL, PRIMARY KEY (Client_ID, Car_ID) ); If you really wanted to do this the relational way you would use InnoDB (or BDB) and use foreign keys as well. CREATE TABLE Clients_R_Cars ( Client_ID INT NOT NULL, Car_ID INT NOT NULL, INDEX client_id_ind (Client_ID), INDEX car_id_ind (Car_ID), FOREIGN KEY (Client_Id) REFERENCES Client(Client_Id) ON DELETE CASCADE ON UPDATE CASCADE, FOREIGN KEY (Car_Id) REFERENCES Car(Car_Id) ON DELETE CASCADE ON UPDATE CASCADE, PRIMARY KEY (Client_ID, Car_ID) ) TYPE=InnoDB; Josh -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
