Try SELECT code,sum(number) AS sum_number FROM $serverTabl_4 GROUP BY code where you've explicitly given the calculated column a name.

I'm pretty sure that DBI doesn't have sexy handling to make up purty column names for the hash-refs. You're going to need to do that yourself or wind up with undef() for keys in your hashes.

updateYeah, merlyn nailed it much clearer than I and diotalevi is right... hashes is magical. :)