Best index strategies for read-only table?
If the ID column is not used for data retrieval, I suggest you place the clustered index on the PROVINCE_ID, CANDIDATE_NUMBER columns instead.

If some columns are read very often compared to others, consider adding an index with PROVINCE_ID, CANDIDATE_NUMBER plus that column. That way the queries can get everything they need from the index itself and don't need to look at the table at all.