In an approach for database index optimization, a processor detects a pattern of characters and numeric digits of an index key. The index key provides an access to a database through an index access without a sorting operation. A processor determines a converting format based on the pattern of the index key. The pattern includes a string of the numeric digits. A processor converts the index key into a converted key by converting the string of the numeric digits into an integer. A processor saves the converted key into a storage.