mysql - ALTER TABLE 添加约束

Question

用户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)
)

不知道为什么？

我以此为引用 http://www.w3schools.com/sql/sql_foreignkey.asp

Error 1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '( ADD CONSTRAINT userPropertie FOREIGN KEY(properties) REFERENCES Properties(' at line 2

Answer 1

省略括号:

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