Grégoire Dubois wrote:
> Victoria Reznichenko wrote:
>> On Friday 04 April 2003 15:37, GrÃ©goire Dubois wrote:
>>> In the following table, I declare ID as a PRIMARY KEY. Is it then
>>> necessary to add the parameters NOT NULL AUTO_INCREMENT?
>>> CREATE TABLE company (
>>> ID INT NOT NULL AUTO_INCREMENT,
>>> name VARCHAR(30),
>>> admin_ID INT,
>>> PRIMARY KEY ID,
>>> INDEX admin_ID,
>>> Or can I just declare the table like that? Does creating a primary key
>>> on an int immediatly involve this one to be not null, and to
>> NOT NULL - yes, but if you want to have AUTO_INCREMENT column you
>> should declare it as AUTO_INCREMENT.
> Thank you very much for your reply.
> But I read that a PRIMARY KEY is a "globally unique identifier" for a
> table. As it is an identifier, it should never be null (ok, that's
> what you said), and it should be unique... Then, if I don't set
> AUTO_INCREMENT to my column ID, it still should be unique, and then
> increment itself... No?
Not all unique identifiers are computer-generated. If you leave off
AUTO_INCREMENT but still make it a primary key, uniqueness will be
enforced on whatever the application(s) enter(s) as the value, but
nothing will be plugged in.