ALTER TABLE add constraint

Question

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; 

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

表已正确创建，但ALTER TABLE不起作用。不知道为什么？

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

错误1064 - 你在你的SQL语法错误;检查对应于你的MySQL服务器版本使用附近的正确语法手册“（ ADD CONSTRAINT userPropertie 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)