> 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?
The issue you are dealing with is skewed data. Most rows have 'N', a few
have 'Y'. Your data is not evenly distributed ... it's skewed.
Bitmap indexes are a solution, but not a solution for this issue. What you
are looking for is histograms. If they won't work for you (because you're
using bind variables) an alternate solution is to code two SQL's in PL/SQL
using an IF statement ... IF :x = 'N' then ... execute the SQL that's hinted
to not use the index, ELSE execute the SQL that's hinted to use the index.
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Author: Greg Moore
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