mysql constraint field uniqueness

Application scenarios

In the daily development of our software, there are often unique constraints that require a certain field value, such as: mobile phone number, email address...

sql operation

1. Create a user table

create table user(
	id varchar(255) comment '主键id',
	name varchar(255) comment '用户名',
	phone varchar(11) comment '手机号',
	email varchar(64) comment '邮箱地址',
	primary key(id)
) comment '用户表';

2. Insert two pieces of data

INSERT INTO `test_db`.`user` (`id`, `name`, `phone`, `email`) VALUES ('2871c6db-2e4f-11e8-9242-00163e06348c', 'Kevin', '18233339999', '[email protected]');
INSERT INTO `test_db`.`user` (`id`, `name`, `phone`, `email`) VALUES ('42895546-2e4f-11e8-9242-00163e06348c', 'Nana', '18233339999', '[email protected]');

3. Observe two data (the mobile phone number is the same, the requirement is that the mobile phone number is not allowed to be the same)

4. Modify to add a unique constraint to the phone field

alter table user add unique(phone);    -- 注意执行这步前需要把重复的字段值删除或者备份一下数据

5. After adding a unique constraint, inserting a duplicate value into the phone field will result in an error