ok, that makes it easy then 🙂
When you create your table, you'll need an id field, give this field the "auto_number" attribute and make it the primary key.
That way, everytime you insert a record it will automatically give it a unique id, allowing you to keep them unique.
So for example, you wanted a news posting table, you would use this to create it:
CREATE TABLE `temp` (`id` INT UNSIGNED NOT NULL AUTO_INCREMENT, `username` VARCHAR( 255 ) NOT NULL ,
`timestamp` TIMESTAMP NOT NULL , `body` TEXT NOT NULL ,
PRIMARY KEY ( `id` ) );