将mysql表从latin1转换为utf8

我正在尝试将一些mysql表从latin1转换为utf8。我正在使用下面的命令,这似乎是最有效的。

ALTER TABLE tablename CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;

以下是如何再现问题:

CREATE TABLE `example` (   `name` char(20) CHARACTER SET latin1 NOT NULL,
  PRIMARY KEY (`name`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1;

INSERT INTO example (name) VALUES ('Drü'),('Dru'),('Patrick'),('Påtrìçk');

ALTER TABLE example convert to character set utf8 collate utf8_general_ci;
ERROR 1062 (23000): Duplicate entry 'Dru' for key 1