How to set unique field in mysql

Mysql method to set unique fields: 1. Add uniqueness constraints when creating the table, the code is [`Id` int(11) NOT NULL AUTO_INCREMENT]; 2. Add uniqueness to the already built table Sexual constraints, the code is [ALTER TABLE `t_user` ADD].

Mysql method of setting unique fields:

1. Add uniqueness constraints when creating the table

CREATE TABLE `t_user` (
`Id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(18) NOT NULL unique,
`password` varchar(18) NOT NULL,
PRIMARY KEY (`Id`)  www.2cto.com  
) ENGINE=InnoDB AUTO_INCREMENT=1018 DEFAULT CHARSET=gbk;

2. Add unique constraints to the already created table

ALTER TABLE `t_user` ADD unique(`username`);

More related free learning recommendations:mysql tutorial(video)

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