At 16:32 -0700 7/29/02, Desmond Lee wrote: >Hello > > >Just wnated to calrify something here. > >If you define your id in a table to be a primary key, do you also >need to define it as 'NOT NULL' and 'UNIQUE'. > >I've notice in some examples like the following off the mysql site: >CREATE TABLE animals ( > id MEDIUMINT NOT NULL AUTO_INCREMENT, > name CHAR(30) NOT NULL, > PRIMARY KEY (id) > ); >that they say the id col is not null, but do they have to since >they've already defined it to be a primary key?
A PRIMARY KEY must be defined to be NOT NULL, a UNIQUE index need not be. If you define a column as AUTO_INCREMENT, MySQL will automatically define it as NOT NULL (at least, it will as of some 3.23.xx version of MySQL). If you define a column as a PRIMARY KEY and as UNIQUE, you may end up with two unique indexes on the column, so you don't want to do that. >Thanks > >Desmond --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
