ALTER TABLE ADD CONSTRAINT 出现错误 1064

Question

用户表和属性表已正确创建。

CREATE TABLE Properties
(
    ID int AUTO_INCREMENT,
    language int,
    stonecolor int,
    gamefield int,
    UserID int,
    PRIMARY KEY(ID),
    FOREIGN KEY(language) REFERENCES Language(ID),
    FOREIGN KEY(stonecolor) REFERENCES StoneColor(ID),
    FOREIGN KEY(gamefield) REFERENCES GameField(ID)
) ENGINE = INNODB;

CREATE TABLE User
(
    ID int AUTO_INCREMENT,
    vorname varchar(30) NOT NULL,
    name varchar(30) NOT NULL,
    email varchar(40) NOT NULL,
    password varchar(40) NOT NULL,
    nickname varchar(15) NOT NULL,
    score int,
    isadmin int DEFAULT 0,
    gamesPlayed int,
    properties int NOT NULL,
    PRIMARY KEY(ID),
    UNIQUE (email),
    UNIQUE (nickname)

) ENGINE = INNODB;

但是

ALTER TABLE User

不起作用。

ALTER TABLE User 
(
    ADD CONSTRAINT userPropertie
    FOREIGN KEY(properties)
    REFERENCES Properties(ID)
)

不明白为什么？

我用这个作为参考：http://www.w3schools.com/sql/sql_foreignkey.asp

错误 1064 - 您的 SQL 语法有错误；检查与您的 MySQL 服务器版本相对应的手册，了解在 '( 附近使用的正确语法 添加约束用户属性 外键（属性） 参考属性（'第 2 行

Answer 1

省略括号：

ALTER TABLE User 
    ADD CONSTRAINT userProperties
    FOREIGN KEY(properties)
    REFERENCES Properties(ID)

Answer 2

ALTER TABLE `User`
ADD CONSTRAINT `user_properties_foreign`
FOREIGN KEY (`properties`)
REFERENCES `Properties` (`ID`)
ON DELETE NO ACTION
ON UPDATE NO ACTION;

Answer 3

alter table User 
    add constraint userProperties
    foreign key (properties)
    references Properties(ID)