Question

Here’s my table:

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   

I want to delete the column photo_id, which presumably will also require deleting the foreign key constraint and the index.

The problem is that I get errors when I try to drop the column:

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

… when I try to drop the index (same as above), and when I try to drop the foreign key constraint:

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

What order should I be doing all of this in? What precise commands should I be using?

Answer 1

The sure thing is to make a duplicate table.

> 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; 

If there’s an error executing RENAME TABLE, some other tables might have foreign key constraints referencing this table, in which case this whole approach is stupid. 🙂