Database Bitmap index

Question

I don't understad why bitmasps indexes are useful:

Ident. Name Gender  Bitmaps
                    F     M
1   Ann     Female  1   0
2   John    Male    0   1
3   Jacob   Male    0   1
4   Pieter  Unsp.   0   0
5   Elise   Female  1       0

If query need to find all person with some Gender - it is clear. But when e.g. need to find all that name starts from "J" ?

Tony Andrews · Accepted Answer · 2011-08-31 13:41:59Z

6

Bitmaps are generally useful only for columns like Gender where the number of distinct values is fairly small. You would not use a bitmap index on names. They are also more useful in data warehousing than in OLTP databases due to the higher cost of maintaining bitmap indexes.

One advantage of bitmap indexes is that a number of them can be ANDed and ORed together to answer queries very efficiently.

edited Aug 31, 2011 at 13:41

answered Aug 31, 2011 at 11:32

Tony Andrews

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