how can I modify table structure to make this query run

CREATE TABLE `renters` (
  `id` int(11) NOT NULL auto_increment,
  `first_name` varchar(100) default NULL,
  `last_name` varchar(100) default NULL,
  `email1` varchar(100) default NULL,
  `email2` varchar(100) default NULL,
  `email3` varchar(100) default NULL,
  `phone1` varchar(20) default NULL,
  `phone2` varchar(20) default NULL,
  `phone3` varchar(20) default NULL,
  `information` varchar(4000) default NULL,
  `description` varchar(9000) default NULL,
  PRIMARY KEY  (`id`),
  UNIQUE KEY `email1` (`email1`)
) ENGINE=MyISAM AUTO_INCREMENT=32 DEFAULT CHARSET=utf8$$








INSERT INTO renters (first_name,last_name,email1,email2,email3,phone1,phone2,phone3,information,description) VALUES ('test','','derrickjmiller1@gmail.com','','','','','','','') ON DUPLICATE KEY UPDATE renters set description=concat(description,'somthing to add to description')

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'set description=concat(description,'somthing to add to description')' at line 1




how can I modify table structure to make this query run

to add to column description in that row where email1 is there