Victoria Reznichenko wrote:
On Friday 04 April 2003 15:37, Grégoire 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
auto-incrИment?
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.
Bruce Feist
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