I have seen older systems store all data as characters. In your initial ETL to the SQL Server I would encourage proper conversions (make date fields DATE or DATETIME2(n) , ... numbers as perhaps DECIMAL(m,n), .. etc). Also if more real time reporting for the accounting data is required, consider transactional replication to the warehouse from the SQL Server source. You can take monthly snapshots per account and sum up the latest snapshot to the transactions within the current month so that real time reporting aggregates do not have to consider too many rows.