rails - created_at when user for ordering, Should you add an Index to the table?

Question

Hello for one of my models photos I have:

default_scope :order => 'photos.created_at DESC, photos.version DESC'

Given that I'm ordering by CREATED_AT and Version... Should I have a DB index on CREATED_AT?

Thanks

Answer 1

One trick that may be helpful: in typical MySql/ActiveRecord models, you will have id as a numeric primary key (hence implicitly indexed), which should be in the same order of created_at - which means you could order by id instead and get the fast performance, without the write cost for an extra index.