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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