Mysql，未能创建外键

Question

这些列只是int（10）。外表列是主键。为什么这个错误？

引用表：

mysql> describe civicrm_entity_financial_account; 
+----------------------+------------------+------+-----+---------+----------------+ 
| Field    | Type    | Null | Key | Default | Extra   | 
+----------------------+------------------+------+-----+---------+----------------+ 
| id     | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| entity_table   | varchar(64)  | NO |  | NULL |    | 
| entity_id   | int(10) unsigned | NO |  | NULL |    | 
| account_relationship | int(10) unsigned | NO |  | NULL |    | 
| financial_account_id | int(10) unsigned | NO |  | NULL |    | 
+----------------------+------------------+------+-----+---------+----------------+ 

参考表：

mysql> describe civicrm_financial_account; 
+-----------------+------------------+------+-----+---------+----------------+ 
| Field   | Type    | Null | Key | Default | Extra   | 
+-----------------+------------------+------+-----+---------+----------------+ 
| id    | int(10) unsigned | NO | PRI | NULL | auto_increment | 
| name   | varchar(255)  | NO |  | NULL |    | 
| account_type_id | int(10) unsigned | NO |  | NULL |    | 
+-----------------+------------------+------+-----+---------+----------------+ 

SQL命令：

ALTER TABLE `civicrm_entity_financial_account` ADD CONSTRAINT `FK_civicrm_entity_financial_account_financial_account_id` FOREIGN KEY (`financial_account_id`) REFERENCES `civicrm_financial_account` (`id`); 


ERROR 1215 (HY000): Cannot add foreign key constraint 

Answer 1

首先，你要确保你的表引擎InnoDB，不MyISAM ，因为后者不支持外键。如果是这样的话，你可以改变发动机：

ALTER TABLE table_name ENGINE = InnoDB; 

如果这不是问题，你可以通过运行检查特定的错误：

SHOW ENGINE INNODB STATUS\G 

，然后在寻找LATEST FOREIGN KEY ERROR部分。

祝你好运！