CREATE TABLE IF NOT EXISTS `mm_Company2County` (
  `companyId` int(10) unsigned NOT NULL,
  `countyId` int(10) unsigned NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

INSERT INTO `mm_Company2County` SELECT id, countyId FROM `mm_Company` WHERE countyId IS NOT NULL;

ALTER TABLE `mm_Company2County` ADD PRIMARY KEY (`companyId`,`countyId`), ADD KEY `countyId` (`countyId`);
ALTER TABLE `mm_Company2County`
  ADD CONSTRAINT `mm_Company2County_ibfk_2` FOREIGN KEY (`countyId`) REFERENCES `mm_County` (`id`) ON UPDATE CASCADE,
  ADD CONSTRAINT `mm_Company2County_ibfk_1` FOREIGN KEY (`companyId`) REFERENCES `mm_Company` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;

ALTER TABLE `mm_Company` DROP FOREIGN KEY `mm_Company_ibfk_2`;
ALTER TABLE `mm_Company` DROP `countyId`;