Ruby on Rails

Personally I would just use the raw sql in a call to delete_all. A
complicated use of arel isn't necessarily "better" or easier to use
than sql (portability concerns aside, but then the whole idea that you
can move any significantly sized app just by changing a line in
database.yml is a bit of a myth anyway).

you could do something like

   class Event < ..
     def self.duplicate_events
       event_alias = Event.arel_table.alias
       scoped.joins(event_alias).where(:subject_id =>
event_alias[:subject_id], ...).where(Event.arel_table[:id].gt(event_alias[:id]))
     end
   end