On 04/19/2015 11:41 AM, Mark W. Farnham wrote:
Nice thread. A side note regarding when a highly dominant value is present, be it 99/1 or 80/2/2/2/2/2/2/2/2/2/2 or <you get the idea>,
then it is often useful to define the physical storage of the dominant value as NULL. (You can interpret a mapping of NULL to a value notwithstanding that the RDBMS must not without an NVL call).
When this can usefully be done a few things happen:
1)If it is a single column index, the index becomes relatively tiny AND the CBO automatically has to avoid the index when searching for NULL, because NULLs are not even in the index. Thus you either get a more appropriate index selection or an appropriate full table or partition scan set scan.
