Migrations allow you to use Ruby to define changes to your database schema, making it possible to use a version control system to keep things synchronised with the actual code.
For further explanation see UnderstandingMigrations, UsingMigrations, OracleAddIndex
API docs: http://api.rubyonrails.com/classes/ActiveRecord/Migration.html
category: Glossary
Supported Databases:
Migrations are currently supported in MySQL, PostgreSQL, SQLite, SQL Server, and Oracle (all supported databases except DB2).