Can not partition existings tables

[Olivier Bourdon]

Hello

I have a few already created tables that I'd like to partition but I always hit error message like
ERROR 1503 (HY000): A PRIMARY KEY must include all columns in the table's partitioning function

whatever partitioning method I use (LIST or HASH)
I know what it basically means because the of restrictions of the partitioning functions but can not determine how I should transform my tables to be able to use partitioning

Note I am using mysql 5.1.47 but can easily migrate to 5.5.3 if required

Here is definition of one table
and the field I'd like to partition on is seg_id which as a finite set of values (around 30)

mysql> show create table Items\G;
Table: Items
Create Table: CREATE TABLE `Items` (
`db_id` bigint(20) NOT NULL AUTO_INCREMENT,
`last_modified` datetime NOT NULL,
`created` datetime DEFAULT NULL,
`digest` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`is_active` bit(1) NOT NULL,
`seg_id` bigint(20) DEFAULT NULL,
`name` varchar(255) COLLATE latin1_general_cs NOT NULL,
`arch` varchar(20) COLLATE latin1_general_cs DEFAULT NULL,
`version` varchar(40) COLLATE latin1_general_cs DEFAULT NULL,
`l_release` varchar(60) COLLATE latin1_general_cs DEFAULT NULL,
`type` varchar(64) COLLATE latin1_general_cs DEFAULT NULL,
`parent_uri` varchar(255) COLLATE latin1_general_cs NOT NULL,
`fullname` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`origname` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`soft_group` varchar(60) COLLATE latin1_general_cs DEFAULT NULL,
`summary` text COLLATE latin1_general_cs,
`l_license` varchar(120) COLLATE latin1_general_cs DEFAULT NULL,
`installed_size` bigint(20) DEFAULT NULL,
`l_file_date` datetime DEFAULT NULL,
`l_done_date` datetime DEFAULT NULL,
`l_url` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`is_fake` bit(1) DEFAULT NULL,
`is_finished` bit(1) DEFAULT NULL,
`flag` int(11) DEFAULT NULL,
`l_source` varchar(120) COLLATE latin1_general_cs DEFAULT NULL,
`binary_uri` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`location` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`uri` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`description` text COLLATE latin1_general_cs,
`size` bigint(20) DEFAULT NULL,
`md5sum` varchar(255) COLLATE latin1_general_cs DEFAULT NULL,
`binary_uploaded` bit(1) DEFAULT NULL,
`l_status` bigint(20) DEFAULT NULL,
PRIMARY KEY (`db_id`),
UNIQUE KEY `is_active` (`is_active`,`seg_id`,`name`,`arch`,`version`,`l_release`,`type`,`parent_uri`),
KEY `ix_l_source` (`l_source`),
KEY `ix_l_origname` (`origname`),
KEY `ix_l_fullname` (`fullname`),
KEY `ix_l_ac` (`is_fake`),
KEY `ix_l` (`seg_id`,`name`),
KEY `fk_l_status` (`l_status`)
) ENGINE=MyISAM AUTO_INCREMENT=64567419 DEFAULT CHARSET=latin1 COLLATE=latin1_general_cs