Updating statistics when you upgrade the database server
When you upgrade a database to use with a newer database server, you can use the UPDATE STATISTICS statement to convert the indexes to the form that the newer database server uses.
You can choose to convert the indexes one table at a time or for the entire database at one time. Follow the conversion guidelines that are outlined in the HCL OneDB™ Migration Guide.
Migration to a newer database server is the only context in which the UPDATE STATISTICS statement causes table indexes to be implicitly dropped and re-created.