MySQL定义外键的方法是每个学习MySQL的人都需要掌握的知识，下文就对MySQL定义外键的语句写法进行了详细的阐述，供您参考。

外键为MySQL带来了诸多的好处，下面就为您介绍MySQL定义外键的语句写法，以及定义外键过程中出现错误的处理方法，供您参考学习。

mysql> CREATE TABLE categories (        -> category_id tinyint(3) unsigned NOT NULL AUTO_INCREMENT,        -> name varchar(30) NOT NULL,        -> PRIMARY KEY(category_id)        -> ) ENGINE=INNODB;  Query OK, 0 rows affected (0.36 sec)   mysql> INSERT INTO categories VALUES (1, ‘SQL Server’), (2, ‘Oracle’), (3, ‘PostgreSQL’), (4, ‘MySQL’), (5, ‘SQLite’);  Query OK, 5 rows affected (0.48 sec)  Records: 5    Duplicates: 0    Warnings: 0   mysql> CREATE TABLE members (        -> member_id INT(11) UNSIGNED NOT NULL,        -> name VARCHAR(20) NOT NULL,        -> PRIMARY KEY(member_id)        -> ) ENGINE=INNODB;  Query OK, 0 rows affected (0.55 sec)   mysql> INSERT INTO members VALUES (1, ‘test’), (2, ‘admin’);  Query OK, 2 rows affected (0.44 sec)  Records: 2    Duplicates: 0    Warnings: 0   mysql> CREATE TABLE articles (        -> article_id INT(11) unsigned NOT NULL AUTO_INCREMENT,        -> title varchar(255) NOT NULL,        -> category_id tinyint(3) unsigned NOT NULL,        -> member_id int(11) unsigned NOT NULL,        -> INDEX (category_id),        -> FOREIGN KEY (category_id) REFERENCES categories (category_id),        -> CONSTRAINT fk_member FOREIGN KEY (member_id) REFERENCES members (member_id),        -> PRIMARY KEY(article_id)        -> ) ENGINE=INNODB;  Query OK, 0 rows affected (0.63 sec)

注意：对于非InnoDB表，FOREIGN KEY子句会被忽略掉。