in order to do this use
AUTO_INCREMENT PRIMARY KEY
while you define your table. Your table should be something like this:
CREATE TABLE `order` (
`order_id` INT(11) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
`user_group_id` INT(11) UNSIGNED NOT NULL,
`status` BIT,
`meta` VARCHAR ( 255 ),
`value` TEXT,
`update_time` TIMESTAMP
)DEFAULT CHARSET = utf8;
remember that you could change other columns, the important one is order_id
which is auto increment