1075 error: Incorrect table definition; there can be only one auto column and it must be defined as a key

1.sql

SET FOREIGN_KEY_CHECKS=0;
DROP TABLE IF EXISTS `contacts`;
CREATE TABLE `contacts` (
  `sl_no` int(11) NOT NULL auto_increment,
  `date` varchar(255) character set latin1 default NULL,
  `name` varchar(255) character set latin1 default NULL,
  `phone` varchar(255) character set latin1 default NULL,
  `email` varchar(255) character set latin1 default NULL,
  `address` varchar(255) character set latin1 default NULL,
  `city` varchar(255) character set latin1 default NULL,
  `pincode` varchar(255) character set latin1 default NULL,
  `state` varchar(255) character set latin1 default NULL,
  `quantity` varchar(255) character set latin1 default NULL,
  PRIMARY KEY  (`name`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;