Bitmap index
A bitmapped index is a special kind of index that is particularly useful in data warehousing for columns that have a low number of distinct values (low cardinality). For example, Sex (M/F). These indexes become very powerful when one is comparing different low cardinality attributes for many items. Logical operators can also be used to optimise queries.
Example bitmap index:
| Attribute | colspan="2" | Product Number | |||
|---|---|---|---|---|---|
| Attribute/Product | 1 | 2 | 3 | 4 | 5 |
| £100 | 0 | 1 | 0 | 1 | 0 |
| £200 | 1 | 0 | 0 | 0 | 0 |
| £300 | 0 | 0 | 1 | 0 | 1 |
| Garden | 1 | 0 | 0 | 0 | 1 |
| Kitchen | 0 | 1 | 1 | 1 | 0 |
| Dining Room | 0 | 1 | 0 | 1 | 0 |
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