Collecting Statistics on Base Table Columns Instead of Hash Index Columns
The Optimizer substitutes base table statistics for hash index statistics when no demographics have been collected for its hash indexes. Because of the way hash index columns are built, it is generally best not to collect statistics directly on the index columns and instead to collect them on the corresponding columns of the base table. This optimizes both system performance and disk storage by eliminating the need to collect the same data redundantly.
Collect statistics on a hash index or non-sparse join index directly in the following scenarios: