CREATE TABLE `t` (  
   `id` int(10) unsigned NOT NULL AUTO_INCREMENT,  
   `domain` tinytext,  
   PRIMARY KEY (`id`)  
 ) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 

INSERT INTO t(domain) VALUES ('j054,j020,mc032,her302') 

UPDATE t SET domain = (REPLACE(domain, ',her302', '')) WHERE id = 1