Sometimes, you need to use BIGINT columns in your databases, e.g. when working with Twitter whose IDs are over 32 bits long now, and will be 64 bits long soon. After some googling which didn’t bring up any good results, a quick look into the adapter code helps us: # activerecord-3.0.0/lib/active_record/connection_adapters/mysql_adapter.rb # Maps logical Rails types to MySQL-specific data types. de