错误代码1833 Cannot change column used in a foreign

最近修改mysql数据库表中的字段长度时报错，执行更改的sql语句：

ALTER TABLE server_list MODIFY COLUMN server_lip CHAR(25);

报错信息：

1 queries executed, 0 success, 1 errors, 0 warnings

查询：alter table server_list modify column server_lip char(25)

错误代码： 1833

Cannot change column 'server_lip': used in a foreign key constraint 'server_history_ibfk_1' of table 'OMServer.server_history'

原因：server_list表中的server_lip字段为server_history表的外键，server_history建表语句：

CREATE TABLE server_history (

ID int(11) NOT NULL AUTO_INCREMENT COMMENT '主键ID',

history_id int(11) NOT NULL COMMENT '事件ID',

history_ip char(15) NOT NULL COMMENT '事件IP地址',

history_user char(15) NOT NULL COMMENT '事件用户名',

history_datetime datetime NOT NULL COMMENT '事件时间',

db_datetime timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '入库时间',

history_command char(255) NOT NULL COMMENT '事件命令',

PRIMARY KEY (ID),

KEY history_ip (history_ip),

CONSTRAINT server_history_ibfk_1 FOREIGN KEY (**history_ip**) REFERENCES server_list (**server_lip**)

) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8 COMMENT='操作事件表'

解决步骤：

1.锁表

LOCK TABLES server_history WRITE,server_list WRITE;

2.查看是否被锁

3.解除server_history表外键约束

ALTER TABLE server_history DROP FOREIGN KEY server_history_ibfk_1;

4.更改server_list表server_lip字段长度

ALTER TABLE server_list MODIFY COLUMN server_lip CHAR(25);

查看表结构发现已完成字段长度更新

5.新增server_history表外键约束

ALTER TABLE server_history ADD CONSTRAINT server_history_ibfk_1 FOREIGN KEY (history_ip) REFERENCES server_list (server_lip);

6.解除锁定

UNLOCK TABLES;