mysql表的字段怎么设置唯一性 _mysql

mysql表的本家儿键是独一性，但不是本家儿键的字段怎么设置独一性呢，我和大师分享一下设置的方式，我写的经验对你进修mysql有帮忙的话，给我投票、点赞或者保藏！
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需要这些哦
mysql
方式/
1登录mysql，在test数据库中新建一个表，本家儿键是id，后面把chengshi字段设置为独一性：
CREATE TABLE `chengshi` ( `id` int(11) NOT NULL AUTO_INCREMENT, `shengfen` varchar(10) DEFAULT NULL, `chengshi` varchar(10) DEFAULT NULL, `shijian` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8

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2在表中增添一些数据：
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('1','河南','安阳','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('2','河南','郑州','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('3','河南','洛阳','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('4','河南','漯河','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('5','河南','新乡','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('6','河南','濮阳','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('7','河南','焦作','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('8','河南','鹤壁','2019-03-05 10:14:27');
insert into `chengshi` (`id`, `shengfen`, `chengshi`, `shijian`) values('9','河南','开封','2019-03-05 10:14:27');