Deleting columns from Sales_data - which are actually used?

Hi

We are approaching 1000 columns in sales_data and trying to determine what options are available to manage this situation.

I suspect that when our custom series were created, some were created with the update field option, and then changed back.  So the columns were created in sales_data, but I believe the columsn are not used.

Looking at computed_fields table,  if dbname is null,  does that mean the series is not stored and the column is not used?  Could I have the DBA delete those columns, eventhough the name exists in the computed_name field?

Thanks

Marsha