mysql添加UNIQUE约束

对name字段添加unique唯一性约束

1.创建表时添加:

CREATE TABLE user
(
id int NOT NULL AUTO_INCREMENT,
name varchar(255),
PRIMARY KEY (id),
UNIQUE (name)
)

2.表已经存在时添加:

ALTER TABLE user ADD UNIQUE (name)

撤销unique约束

mysql:
    ALTER TABLE user
    DROP INDEX name;