Thanks Don, Your explanation is very helpful.
--- Don Granaman <[EMAIL PROTECTED]> wrote:
> Bitmapped indexes will be fast for the queryagainst
> the 'Y's, but a
> bitmapped index may not be appropriate if you are
> getting lots of DML
> activity on this.
>
> Another option is to use NULL instead of the "vast
> majority" value ('N' - in
> this case) and create an index. The nulls won't be
> indexed, so the index
> will be small. This works best when there are
> relatively few non-majority
> values and they are the ones most
> critically/commonly queried. A hint MAY
> be required to make the CBO use the index. This
> obviousy won't help on
> queries against 'N' though. Example, ORDERS table
> with a STATUS column -
> 98% 'Closed', 2% ('New' | 'Pending' |
> 'Whatever...'). Change the logical to
> interprete NULL as 'Closed' and create an index on
> ORDERS.STATUS. Queries
> for open orders - ('Closed' | 'Pending' |
> 'Whatever...') become very fast.
>
> Don Granaman
> [OraSaurus]
>
> ----- Original Message -----
> To: "Multiple recipients of list ORACLE-L"
> <[EMAIL PROTECTED]>
> Sent: Monday, July 15, 2002 2:58 PM
>
>
> If we have a column of 'Y','N' values, the index
> will
> not help with CBT(usually most of the values are
> 'N').
>
> My question is : how about bitmap indexes? Should it
> help a lot, or just a little bit?
>
> Thanks,
>
> Chris Harvest
>
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