Rolling back a failed Rails migration

Question

How do you roll back a failed rails migration? I would expect that rake db:rollback would undo the failed migration, but no, it rolls back the previous migratio

Answer 1

Unfortunately, you must manually clean up failed migrations for MySQL. MySQL does not support transactional database definition changes.

Rails 2.2 includes transactional migrations for PostgreSQL. Rails 2.3 includes transactional migrations for SQLite.

This doesn't really help you for your problem right now, but if you have a choice of database on future projects, I recommend using one with support for transactional DDL because it makes migrations much more pleasant.

Update - this is still true in 2017, on Rails 4.2.7 and MySQL 5.7, reported by Alejandro Babio in another answer here.