mysql> create table country( -> country_id smallint unsigned not null auto_increment, -> country varchar(50) not null, -> last_update timestamp not null default current_timestamp on update current_timestamp, -> primary key(country_id) -> )engine=innodb default charset=utf8; Query OK, 0 rows affected (0.29 sec) mysql> create table city( -> city_id smallint unsigned not null auto_increment, -> city varchar(50) not null, -> country_id smallint unsigned not null, -> last_update timestamp not null default current_timestamp on update current_timestamp, -> primary key(city_id), -> key idx_fk_country_id(country_id), -> constraint 'fk_city_country' foreign key(country_id) references country(country_id) on delete restrict on update cascade -> ) -> engine=innodb default charset=utf8; ERROR 1064 (42000): 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 ''fk_city_country' foreign key(country_id) references country(country_id) on dele' at line 8
经过测试,问题出在constraint 'fk_city_country' ,这貌似是oracle的写法,MySQL中不需要这个.
看去掉之后,执行成功.
mysql> mysql> create table city( -> city_id smallint unsigned not null auto_increment, -> city varchar(50) not null, -> country_id smallint unsigned not null, -> last_update timestamp not null default current_timestamp on update current_timestamp, -> primary key(city_id), -> key idx_fk_country_id(country_id), -> foreign key(country_id) references country(country_id) on delete restrict on update cascade -> ) -> engine=innodb default charset=utf8; Query OK, 0 rows affected (0.20 sec) mysql> show create table city; +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | city | CREATE TABLE `city` ( `city_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `city` varchar(50) NOT NULL, `country_id` smallint(5) unsigned NOT NULL, `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, PRIMARY KEY (`city_id`), KEY `idx_fk_country_id` (`country_id`), CONSTRAINT `city_ibfk_1` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.03 sec) mysql>
看到这里,发现create table 语句中可以定义CONSTRAINT `city_ibfk_1`啊,仔细想想错误的create 语句与执行成功之后的show create语句之间的差别不就是
CONSTRAINT `city_ibfk_1` 和 CONSTRAINT 'city_ibfk_1' 一个'一个`,看到这里恍然大悟,`是分隔符加在外键名称上是可以的,而且定义外键名字不需要加单引号和双引号,直接命名即可,所以加了'的会报错!
不信再试试看,不加`也不加'试试看效果:
mysql> create table city4( -> city_id smallint unsigned not null auto_increment, -> city varchar(50) not null, -> country_id smallint unsigned not null, -> last_update timestamp not null default current_timestamp on update current_timestamp, -> primary key(city_id), -> key idx_fk_country_id4(country_id), -> CONSTRAINT city1_ibfk_4 foreign key(country_id) references country(country_id) on update cascade -> ) -> engine=innodb default charset=utf8; Query OK, 0 rows affected (0.13 sec)
看到了,搞定成功了,所以在define外键的时候,外键名称不可以添加单引号和双引号。