find_by_sql (ActiveRecord::Base)

find_by_sql (ActiveRecord::Base) - APIdock:

parameter is a full SQL query as a string. It will be called as is, there will be no database agnostic conversions performed. This should be a last resort because using, for example, MySQL specific terms will lock you to using that particular database engine or require you to change your call if you switch engines.

Full article: http://apidock.com/rails/ActiveRecord/Base/find_by_sql/class