SELECT (octet_length(customer_number)) as customer_length, customer_number
FROM [table]
ORDER BY customer_length DESC;

CREATE TABLE `[table]` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `customer_number` text,
  `who` text,
  `what` text,
  `date` datetime DEFAULT NULL,
  `status` text,
   PRIMARY KEY (`id`),
   KEY `index_1` (`customer_number`(8))
) ENGINE=MyISAM AUTO_INCREMENT=4462936 DEFAULT CHARSET=latin1;