ALTER添加约束

Question

正确创建了表用户和属性

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ALTER TABLE User不起作用。

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

不知道为什么吗？

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；请检查与MySQL服务器版本对应的手册，以获得正确的语法以使用userPropertie '(添加约束userPropertie外键(属性)引用属性)(“在第2行

中”)

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)