Major Description
We already have an INDEX hint, and we already have a mechanism to collect referenced columns in the data table that are not in the index table (used only for local indexes currently). Instead of not using the global index when a referenced data column is not found in the index, we should rewrite the query to join back to the data table when the INDEX hint is present. This is always possible, as we always have the data PK columns in the index table, and our join optimization would kick in as well.