Indexes are created using the sort sequence that was in effect when the CREATE INDEX statement was run.
An entry is added to the index every time an insert is made into the table over which the index is defined. Index entries contain the weighted value for character key, and UCS-2 and UTF-16 graphic key columns. The system gets the weighted value by converting the key value based on the sort sequence of the index.
When selection is made using that sort sequence and that index, the character, or UCS-2 or UTF-16 graphic keys do not need to be converted before comparison. This improves the performance of the query.