
Using indexes in Rails - _pius
http://tomafro.net/2009/08/using-indexes-in-rails-index-your-associations
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cloudkj
In the more common cases, you get indexes on foreign keys for free. For
example, using MySQL with InnoDB, declaring a FOREIGN KEY constraint will
automatically create an index on the referencing table:
[http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-
co...](http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-
constraints.html)

