ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your

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。