MySQL(InnoDB):需要删除列,并附带外键约束和索引

Question

这是我的表:

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,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(与上面相同)时,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)

我应该做什么顺序呢？我应该使用哪些精确命令？

Answer 1

准确地说,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`;

上一个命令删除列上的外键约束.现在你可以删除列了photo_id(删除列时MySQL删除了索引):

ALTER TABLE `alums_alumphoto` DROP COLUMN `photo_id`;

或者,您可以将这两个操作合并为一个:

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

Answer 2

肯定的是制作一个重复的表格.

> CREATE TABLE alums_alumphoto_new LIKE alums_alumphoto;
> ALTER TABLE .... // Drop constraint
> ALTER TABLE .... // Drop KEY
> ALTER TABLE .... // Drop the column
> INSERT INTO alums_alumphoto_new (SELECT id, alum_id, photo_id, media_id, updated FROM alums_alumphoto);
> RENAME TABLE alums_alumphoto TO alums_alumphoto_old, alums_alumphoto_new TO alums_alumphoto;

如果执行RENAME TABLE时出错,则其他一些表可能具有引用此表的外键约束,在这种情况下,整个方法都是愚蠢的.:)