MySQL (InnoDB) : need to delete column, 和附带的外键约束和索引

Question

这是我的表格:

CREATE TABLE `alums_alumphoto` (  
  `id` int(11) NOT NULL auto_increment,  
  `alum_id` int(11) NOT NULL,  
  `photo_id` int(11) default NULL,  
  `media_id` int(11) default NULL,  
  `updated` datetime NOT NULL,  
  PRIMARY KEY  (`id`),  
  KEY `alums_alumphoto_alum_id` (`alum_id`),  
  KEY `alums_alumphoto_photo_id` (`photo_id`),  
  KEY `alums_alumphoto_media_id` (`media_id`),  
  CONSTRAINT `alums_alumphoto_ibfk_1` FOREIGN KEY (`media_id`) REFERENCES `media_mediaitem` (`id`),  
  CONSTRAINT `alum_id_refs_id_706915ea` FOREIGN KEY (`alum_id`) REFERENCES `alums_alum` (`id`),  
  CONSTRAINT `photo_id_refs_id_63282119` FOREIGN KEY (`photo_id`) REFERENCES `media_mediaitem` (`id`)  
) ENGINE=InnoDB AUTO_INCREMENT=63 DEFAULT CHARSET=utf8  

我想删除列 photo_id，这可能还需要删除外键约束和索引。

问题是当我尝试删除列时出现错误:

ERROR 1025 (HY000): Error on rename of '.\dbname\#sql-670_c5c' to '.\dbname\alums_alumphoto' (errno: 150)

...当我尝试删除索引(同上)，以及当我尝试删除外键约束时:

ERROR 1091 (42000): Can't DROP 'photo_id_refs_id_63282119'; check that column/key exists)

我应该按照什么顺序执行所有这些操作？我应该使用哪些精确命令？

Answer 1

没错，试试这个:

首先删除外键或约束:

ALTER TABLE `alums_alumphoto` DROP FOREIGN KEY `photo_id_refs_id_63282119`;

前面的命令删除列上的外键约束。现在您可以删除列 photo_id(删除列时 MySQL 会删除索引):

ALTER TABLE `alums_alumphoto` DROP COLUMN `photo_id`;

或者，您可以将这两个操作合二为一:

ALTER TABLE `alums_alumphoto` 
   DROP FOREIGN KEY `photo_id_refs_id_63282119` , 
   DROP COLUMN `photo_id`;