On Nov 28, 11:50 am, Rodrigo Rosenfeld Rosas <[email protected]> wrote: > Also if creating the foreign key won't > automatically create an index to it for some databases, such statement > should also take care of creating the index too.
Postgres does not automatically create indexes for foreign keys, and for good reason. Consider a "categories" table with an id, name, and several other columns. It has only 5 rows. Then you have an "items" table with a million rows. It has a category_id, and you make it a foreign key. Adding an index with such a low cardinality is a Bad Idea™ because 1. it will likely never be used by the query planner 2. it will always slow down all writes to that table. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/rubyonrails-core?hl=en.
