Bitmap Database Index

Question

I do not understand why it is useful to use bitmasps indices:

Ident. Name Gender Bitmaps FM 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 the request needs to be found by the whole person with some kind of gender - this is understandable. But when, for example, you need to find everything that the name begins with "J"?

Answer 1

Raster images are usually only useful for columns such as Gender, where the number of different values ​​is quite small. You would not use the bitmap index for names. They are also more useful in data storage than in OLTP databases, due to the higher cost of supporting raster indexes.

One of the advantages of bitmap indices is that some of them can be AND and ORed together to efficiently respond to requests.