A financial services company needs to run frequent, high-performance queries against a large transaction table. The queries filter transactions based on the year and month of the transaction timestamp, which is stored in a `TRANSACTION_TS` column of data type `TIMESTAMP`. The current query uses `WHERE YEAR(TRANSACTION_TS) = ? AND MONTH(TRANSACTION_TS) = ?`, which results in a full table space scan. How should the DBA improve the performance of these queries?